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  1. They’re still at it: environmental scholar Bjorn Lomborg, citing a 1997 atmosphere-ocean general circulation model, observes that “the increase in direct solar irradiation over the past 30 years is responsible for about 40 percent of the observed global warming.”

    Good ole Pete du Pont. All the deniers are on this sun kick, along with a revisionist history of the LIA, MWP, and out and out libel in my view over the hockey stick flaw. At some point can’t they be held accountable for lying? Is that an unalienable right?

    [Response: If readers en masse refuse to purchase the paper until the editorial board stops using their perch to spread lies and propaganda, the WSJ might think twice next time. In the meantime, a google search on “Wall Street Journal editorial” might make you feel a bit better. –mike]

    Comment by Mark A. York — 21 Feb 2007 @ 12:09 PM

  2. re: the difference between 10 days (aerosols) and 100 years (CO2)

    That’s a nasty conundrum: if we do something about active production of CO2, we accelerate the effects because of the lack of aerosols.

    Does that sound like a recipe for fatalism? You betcha.

    Comment by Jeffrey Davis — 21 Feb 2007 @ 12:16 PM

  3. I’m just terribly grateful to RealClimate for consistently posting this exceptional level of crisp exposition. You folks are really making a difference. Thank you for the generous contribution of your time toward providing this unparalleled forum.

    Comment by Daniel Goodwin — 21 Feb 2007 @ 12:35 PM

  4. One of the big problems with aerosols is that they interact with clouds, that other “great unknown” in climate modelling. If clouds were well-represented by the models then untangling the influence of aersols would be hard enough, but… clouds are poorly represented in models at present [though much improved compared to ~10 years ago].

    To be honest I don’t think this scientific problem is going to be “solved” soon enough to have an impact on the crucial policy decisions of the next 10 years.

    Comment by Timothy — 21 Feb 2007 @ 12:45 PM

  5. RE: Jeffrey (#2)
    I prefer to see it as MORE inspiration to (1) figure out how to reduce CO2 emissions quickly – because the warming we’ve seen so far has been somewhat masked by aerosol, and (2) really work hard to understand all the aerosol climate effects more completely (look at those error bars!)

    Remember also, the warming caused by increased CO2 has a time lag, so the sooner and more rapidly we reduce CO2 emissions, the better. We can do this, we just need to take the problem seriously, especially because of the (more uncertain) aerosol cooling.

    Comment by Juliane Fry — 21 Feb 2007 @ 12:53 PM

  6. “Aerosols are solid or liquid particles suspended in the atmosphere, consisting of (in rough order of abundance): sea salt, mineral dust, …”

    That’s in decreasing order of abundance, I take it? That is, sea salt is the most abundant, followed by mineral dust, etc.? (The wording is a little ambiguous.)

    Comment by Peter Erwin — 21 Feb 2007 @ 1:16 PM

  7. … changes in the anthropogenic portion of aerosols since 1750 have resulted in a globally averaged net radiative forcing of roughly -1.2 W/m2, in comparison to the overall average CO2 forcing of +1.66 W/m2.

    What is a rough range of accuracy for the -1.2 W/m2?

    My thought is that globally averaged net radiative forcing on a decade basis will change only slightly. It’s important not to loose focus on the need to act on drastically reducing our CO2 emissions.

    Comment by pat neuman — 21 Feb 2007 @ 1:24 PM

  8. Very nice explanation, Juliane. Thank you for your insights. I actually just took part in a discussion at Open Mind, in which a skeptic raised this issue of the lack of understanding about the effects of aerosols on our climate, stating that the IPCC’s scientific understanding is “very low”. Like many other skeptics, he was first misrepresenting the actual level of understanding, and then used it as a reason for discounting any scientific statements about the effects of aerosols, because supposedly one must accept too many assumptions.

    Anyways, I appreciate your information on the subject, which clearly demonstrates that, while there is room for improvement, much has already been discovered.

    Comment by Reasic — 21 Feb 2007 @ 1:45 PM

  9. Because we need to decrease GHG emissions dramatically in any scenario, it would seem wiser to reduce as quickly as possible despite additional warming caused by aerosol reductions. The longer we wait, the greater the likelihood that this ultimately unavoidable reduction in aerosols will have an even greater warming related effect.

    Comment by George Ortega — 21 Feb 2007 @ 2:34 PM

  10. Hi Juliane

    thanks for this interesting post

    can we obtain the recent evolution, year by year, of aerosols forcing evolution (since 1990 for example)?
    How can we understand “low level of understanding”?
    Is this the understanding of accurate physical mechanism?
    Does the given range of forcing depend on this understanding or on the measurements?

    Comment by Pascal — 21 Feb 2007 @ 2:46 PM

  11. What is Juliane’s URL?
    Why do I never hear that the CO2 greenhouse effect is saturated ?
    Why do I never see reference to the fact that CO2 absorption is concentrated in a wavelength band centered at 15 micro meters?

    Comment by Richard LaRosa — 21 Feb 2007 @ 2:49 PM

  12. Re #11: “Why do I never hear that the CO2 greenhouse effect is saturated ?”

    Umm… How shall I say this? For much the same reason that you don’t hear a whole lot about the Earth being flat :-)

    Comment by James — 21 Feb 2007 @ 3:21 PM

  13. Juliane, a lecture I attended about a year ago pointed out that one of the problems with constraining aerosols is poor knowledge of their time history. It wasn’t till the middle to late twentieth century that direct measurements on large scales became practical. And because aerosols are often so short lived and so spatially inhomogenous, it is very difficult to reconstruct an adequate picture from proxies like ice core data. As a result, the speaker stated that a large chunk of the uncertainty comes from not having firm constraints on what the natural aerosol loading was circa 1750. I wonder if you could comment on this, and whether any progress is being made in paleo-reconstruction.

    Secondly, could you comment on the degree to which the overall uncertainty is a matter of things that no one yet claims to understand versus areas where different researchers reach mutually incompatible conclusions. I recall that the indirect effect is known to give some examples of the second kind of uncertainty. If I recall correctly, the effect of high sulphate aerosol concentrations on cloud lifetime is one such area, where observational studies and cloud models have been disagreeing even on the sign of the effect (i.e. whether high sulphate leads to longer or shorter cloud lifetimes).


    Comment by Robert A. Rohde — 21 Feb 2007 @ 3:52 PM

  14. Re: #6.

    Yes, that order of aerosol components is in decreasing magnitude by MASS. Mineral dust and sea salt particles are primarily supermicron in diameter and thus constitute the bulk of aerosol mass. Depending on which estimate you read either mineral dust or sea salt it the largest aerosol component by mass.
    However, by number (which matters more for aerosol-cloud interactions) the submicron particle types dominate. These include organic carbon, soot (also known as black carbon or elemental carbon), and secondary aerosol components such as ammonium sulphate and ammonium nitrate. Pure ammonium sulphate rarely exists in the atmosphere (though models often parameterise them this way!) and are typically internally mixed with submicron soot, organic carbon, etc. aerosols. The mixing state of aerosols is a very complicated but important topic that isn’t well represented in aerosol models (and even less so in climate models), partly because the models lack good empirical imputs for these parameters.
    One interesting result of the mixing state concerns ammonium sulphate and soot. Soot is the most absorbing aerosol component and causes a positive radiative forcing. Ammonium sulphate is highly reflective, scatters solar radiation very well, and causes a negative forcing. However, when you have a particle that is internally mixed with soot and ammonium sulphate (say a core of soot with a coating of ammonium sulphate around it), the ammonium sulphate coating acts as a lens to focus light into the absorbing soot core. Thus by mixing the two aerosol components you end up with an overall more absorbing aerosol (higher positive forcing) than when the two aerosol types are externally mixed in their pure forms. This is one of the best examples of why aerosol mixing state is so important for modeling the effect of aerosols on climate.

    Comment by Ryan Sullivan — 21 Feb 2007 @ 4:04 PM

  15. Re: #12 by James. L.D. Danny Harvey, “Global Warming – the Hard Science”, Prentice Hall, pp. 153-156 has forcing vs. CO2 concentration. The 15 micrometer band forcing falls in the logarithmic regime (bottom of p. 155). Fig. 7.11 shows some nonlinearity at twice the pre-industrial CO2 level.

    Comment by Richard LaRosa — 21 Feb 2007 @ 4:14 PM

  16. Believe it or not, skeptics have twisted this revision in aerosols to argue that climate change is not as bad we thought. I blogged about this new argument here.

    Comment by Andrew Dessler — 21 Feb 2007 @ 4:20 PM

  17. I guess “clean coal” (that reduces aerosol aspects, but not the CO2) is not a good solution to environmental problems, even though it would reduce acid rain; better to reduce fossil fuels altogether.

    Re #1, I thought Lomborg was only a “money could best be spent elsewhere” denialist, who admitted that AGW was happening, but his heart went out to the masses suffering from other causes, who should be aided first. So now we see his true motive. And I wonder how much he really cares about the suffering masses.

    And about the sun — without it the whole problem would be moot, including ourselves. So it is a major culprit, the way it just keeps shining and shining. I guess that small “solar irradiance” bar is for the increased shining, and does not represent the total shining?

    Re # 5, I agree with you, Juliane, that we need to reduce GHGs, even though those same measures might reduce the cooling aerosol effect.

    Somehow I wouldn’t worry about us reducing too fast, even if we put our whole heart, mind, soul, and effort into it (& all the contrarians converted to AGW believers & really started helping solve the problem, rather than dragging their feet kicking & screaming). Even in the best case reduction scenario the logistics are tremendous; it would take decades to get us down to the 70% money-saving cuts that are feasible with today’s technology, and a decade or so more to get the rich of the world (us) to actually sacrifice and reduce our living standards so as to get down to an 80%+ cut.

    I know an architect who build a passive solar home that uses only a fraction of the gas & electricity of a comparable home (& that’s without PV panels). Considering all the homes & buildings now going up WITHOUT even the passive techniques that don’t have additional costs & that have been known about and practiced for over 2,500 years (see: )….Today’s home are flagrantly inefficient….it seems like a big job to get architects to change habits. And then those wrongly-built houses & buidlings are here for decades to come. It really breaks my heart that at the first whiff of a problem (the 70s energy crunch) the field of architecture didn’t completely (or even somewhat) embrace passive solar techniques.

    Comment by Lynn Vincentnathan — 21 Feb 2007 @ 4:34 PM

  18. Wow. “aerosols remain the least understood component of the climate system.”
    Aerosols have a net radiative forcing of -1.2 W/m2 against a CO2 forcing of 1.66 W/m2. If I were an AGW convictee, the closeness of these figures along with the uncertainty regarding aerosols would concern me.

    Comment by PHE — 21 Feb 2007 @ 4:49 PM

  19. Good article! But I do have to echo #10: what exactly does “low level of understanding” mean?

    I take it to mean that we’re pretty sure about the direction of net forcing due to aerosols is, but we need more information to pin down the magnitude. Is this pretty accurate?

    The reason I ask is because the length of the error bars in the “low understanding” categories vary a lot.

    Re 11:
    I’m confused about why you’d expect this article to address C02 as a greenhouse gas. There is plenty of information on this website about that topic. You clearly intended to say something with your questions, but I don’t get it…

    Comment by Marcus L. — 21 Feb 2007 @ 5:01 PM

  20. Scientists are acting as enablers, this is a social issue not a scientific one. I think scientists should show the world some tough love.

    Comment by Paul M — 21 Feb 2007 @ 6:12 PM

  21. Re: Post #20 by Paul M.
    …..I think scientists should show the world some tough love…..

    Paul, that’s a very astute comment. Thank you.

    Comment by salamander — 21 Feb 2007 @ 6:37 PM

  22. I would like to know the calculation behind this part of the article:

    A CO2 molecule has a lifetime of about 100 years in the atmosphere, while an aerosol particle has an average life expectancy of only about 10 days. Therefore, if we instantaneously ceased using combustion engines, the (cooling) fossil fuel-related aerosols would be cleaned out of the atmosphere within weeks, while the (warming) CO2 would remain much longer, leaving a net positive forcing from the reduction in emissions for a century or more.

    First, I think it is more accurate to describe the lifetime of CO2 as half will be gone in 20 years, while 20% will remain in the air for centuries (at least according to this).

    I would phrase the question as comparing the impact of running a coal plant for 100 years compared to replacing it with a clean energy source. The aerosol forcing of the coal plant will remain constant over the century, while the carbon dioxide impact will gradually accumulate. The key values, which I do not know, are the forcings from the amount of aerosol and CO2 emitted from the plant.

    I find it surprising it takes a century of CO2 emissions to catch up to the aerosol forcing. It means that any action we take to reduce CO2 emissions will be effective on a longer time scale than I thought (which was already long), and the net effect will be less.

    [Response: That’s exactly right: Juliane got that part wrong. We’ve been trying very hard to set the record straight. It is wrong to say that a CO2 molecule has a lifetime of “about 100 years” in the atmosphere. It takes more like 500-1000 years for the ocean to remove 80% of the Co2, and there’s a tail that extends for at least 10,000 years. Don’t know how we overlooked that, but c’est la vie. See David Archer’s article on CO2 lifetime in the archives. In any event, the main thrust of Julianne’s point, which is that CO2 stays around for a long time but aerosols disappear fast, is even more valid. Since sulfate pollution and other things that go with dirty coal have a lot of adverse environmental consequences one needs to get rid of, this just means one has to work even harder at reducing CO2. –raypierre]

    Comment by Blair Dowden — 21 Feb 2007 @ 7:53 PM

  23. #18’s comment reminded me of another point that is often lost when discussing the climate effects of aerosols. The numbers given by the IPCC are GLOBAL averaged forcings. Aerosols, due to their short lifetimes, are not everly dispersed throughout the atmosphere the way greenhouse gases are (with the main exception being ozone). The aerosol burden in one region might be quite positive (due to high soot loadings as a simple example) while in another it might be strongly negative (due to high ammonium nitrate and organic carbon loadings from agricultural areas, for example). Thus, the REGIONAL climate impacts of aerosols really need to be considered, particularily their effects on precipitation. It is too simplistic to think that the negative (and quite uncertain) forcing of aerosols cancels out most of the positive forcings of GHG. Though it is easy to see how this misconception arises.

    Comment by Ryan Sullivan — 21 Feb 2007 @ 8:50 PM

  24. Re #22: Somewhat closer to home, we have this article which gives a mean lifetime of about 30,000 years for a CO2 molecule, with the warning that this is a bit misleading due to the nonlinearity (or perhaps I should say the non-logarithmic linearity) of the decay process. It would be nice if we could agree on a metric for CO2 atmospheric lifespan to avoid confusion, but I’m too confused to propose a good one.

    Comment by S. Molnar — 21 Feb 2007 @ 9:20 PM

  25. Remember also, the warming caused by increased CO2 has a time lag

    What is the lag time?

    Comment by joel — 21 Feb 2007 @ 9:30 PM

  26. Re #22 This question has been addressed in an earlier post,
    Water vapor: feedback or forcing?
    In the green comments to comment #85.

    Here is an engineer’s view of the problem –
    Residence time of atmospheric CO2

    Bottom line – CO2 residence times are much longer than 20 years.

    Hope this helps (and the links work)

    Comment by J. Althauser — 21 Feb 2007 @ 9:52 PM

  27. Re #26 and my own #24: Thanks for the link to Professor Lam’s paper. I am happy to accept his metric, which gives an answer for practical purposes of about 400 years, which is consistent with the rule of thumb given in the RC post I linked.

    Comment by S. Molnar — 21 Feb 2007 @ 10:13 PM

  28. So how fast is the science on this advancing? How important is this level of scientific understanding to the accuracy of the climate models. And how much does each of those LOSU values contribute to the uncertainties in the IPCC warming estimates?

    Comment by Craig Allen — 21 Feb 2007 @ 10:25 PM

  29. My question is this: Doesn’t the uncertainty in the aerosol forcing imply equivalent uncertainty in the other anthropogenic forcings? Since the overall increase in ghg related emissions is highly correlated if looked at averaged over the whole 200 years since industrialisation, error or uncertainty in one would imply more uncertainty in the balance between forcings, but less in the overall forcing than you’ve shown. I thought the overall forcing would have been calculated and cross-checked against the measured overall temperature differential. I imagined this to be quite accurate. On the other hand, when CO2 concentrations are increasing, and aerosols are decreasing (say due to the collapse of dirty eastern-bloc industries) it would be hard to tease out which was causing observed increases in temperature.

    Comment by Marco Parigi — 21 Feb 2007 @ 10:43 PM

  30. In reply to Marcus L. #19, this article compares CO2 and aerosol forcing and examines the incremental change in forcing due to incremental changes in CO2 and aerosol concentrations. It is important to note that a certain percentage change in CO2 produces a smaller percentage change in forcing due to nonlinearity. I wonder if the climate forcing of a given aerosol (whatever this may mean, since aerosol concentrations are regional, as pointed out in #23 by Ryan Sullivan) is linearly related to its local concentration.

    Also, CO2 absorption is due to molecular resonance and is narrow-band. Aerosol scattering is described (I think) by geometrical optics and is broad-band, compared to CO2. Radiation to space at the CO2 resonant frequency takes place from a much higher altitude than the reflection of short-wave sunlight or thermal equilibrium long-wave IR radiation from an aerosol.

    While trying to write an intelligent comment I realize how complicated this stuff is. Enough already!

    Comment by Richard LaRosa — 21 Feb 2007 @ 11:29 PM

  31. The uncertainty in aerosol forcing looks unsettling, but this is a good example of the case where one needs to ask: What are the consequences of this uncertainty for our predictions of future climate? One way that the uncertainty affects the future is through the warming due to the decline in aerosols if we move to cleaner burning technologies. If the present forcing is large, the warming due to aerosol decline willl be larger, and conversely. The uncertainties in aerosol forcing also have some consequences for deciding which models have the “best” climate sensitivity, though the precise implications of that are a bit harder to see. One thing to keep in mind is that, if CO2 continues to increase, the CO2 increasingly overwhelms the aerosol forcing, so aerosol uncertainty may play less role in the future than in the past century. A further thing to notice is that, as one commenter mentioned, the aerosols are not uniformly distributed; there’s considerable regional variation. That means that a climate with a lot of CO2 warming partially offset in the global average by a lot of regional aerosol cooling is still a very different climate than one with no anthropogenic aerosols and less CO2. It’s still, as Hansen says, a different planet we’ll be living on.

    I’d be interested in hearing more discussion from the aerosol experts here about what it would imply for the aerosol forcing to be on the low end of the range, vs. what it would imply for the aerosol forcing to be on the high end of the range.

    Keep in mind also that, while the article chose to compare just CO2 radiative forcing with aerosols, there are other anthropogenic greenhouse gases. You could just as well take the sum of radiative forcing from the “lesser” greenhouse gases: CH4, N2O,halocarbons and ozone, which amount to about 1.2 W/m**2, and net them against roughly 1.2 W/m**2 of aerosol cooling. Put that way, you’d say the midrange estimate of aerosol forcing cancels out the radiative forcing from the lesser greenhouse gases, leaving us with the full effect of CO2 as if the “complications” weren’t there. Or, Jim Hansen, for some reason, likes (or liked) to say that the aerosols canceled out most of the CO2 radiative forcing, leaving us to see a little of CO2 plus a lot from the other greenhouse gases. That’s no more nor less valid, but it did open up his paper to a lot of misinterpretations by the media, which then got the message that Methane’s the problem, not CO2. The fact is that for the greenhouse gases, radiative forcing is radiative forcing, and it doesn’t make much sense to break it apart when comparing to aerosols. It makes sense to break it apart mainly because the different gases have different atmospheric lifetimes

    Comment by raypierre — 21 Feb 2007 @ 11:34 PM

  32. I have a question not directly related to the topic of aerosols but to a point that someone brought up higher in the discussion. Chevron and other big combustion players maintain blogs on which there are seemingly inexhaustible supplies of skeptics who can sound technical enough to be convincing for most of the general public. One of their favorite battle horses is the absorbtion spectrum of CO2, which they maintan is too narrow to account for the forcing attributed to the gas. Any help on that?

    [Response: See the discussion of the spectrum of CO2 absorption in Dave Archer’s global warming text, and play with the online models. For a more technical discussion, take a look at my climate textbook (draft online, chapter 4, see ), or Goody and Yung. We don’t have an article on this because only the least informed skeptics are using the argument anymore, and nobody of any consequence believes it. Perhaps we ought to have something like that in the wiki, for general education. –raypierre]

    Comment by Philippe Chantreau — 21 Feb 2007 @ 11:43 PM

  33. RE: 22

    An estimate of anthropogenic CO2 inventory from decadal changes in oceanic carbon content
    Proceedings of the National Academy of Sciences, (2007)

    …”Approximately half of the anthropogenic carbon released to the atmosphere from fossil fuel burning is stored in the ocean, although distribution and regional fluxes of the ocean sink are debated. Estimates of anthropogenic carbon (Cant) in the oceans remain prone to error arising from (i) a need to estimate preindustrial reference concentrations of carbon for different oceanic regions, and (ii) differing behavior of transient ocean tracers used to infer Cant.”…”In contrast to prior approaches, the results are independent of tracer data but are shown to be qualitatively and quantitatively consistent with tracer-derived estimates. The approach reveals more Cant in the deep ocean than prior studies; with possible implications for future carbon uptake and deep ocean carbonate dissolution. Our results suggest that this approachs applied on the unprecedented global data archive provides a means of estimating the Cant for large parts of the world’s ocean.”

    Distribution and inventory of anthropogenic CO in the Southern Ocean: Comparison of three data-based methods
    Journal of Geophysical Research 110 (c9), 09-2 (2005)

    …”North of 50°S, distribution and inventories of Cant are coherent with previous data-based and model estimates, but we found larger storage of Cant south of 50°S as compared to the midlatitude region. In that, our results disagree with most previous estimates and suggest that the global inventory of anthropogenic CO2 in the Southern Ocean could be much larger than what is currently believed.”

    Response to Comment on “The Ocean Sink for Anthropogenic CO2”
    Science 308 (5729), 1743d (2005)
    ….”The correct determination of the magnitude and uncertainty of the oceanic uptake of anthropogenic CO2 and of the climate change feedbacks is of prime relevance to constrain the net balance of the terrestrial biosphere over the past 200 years”..

    Climate-carbon cycle feedbacks under stabilization: uncertainty and observational constraints
    Tellus B 58 (5), 603 (2006)
    …”However, the observational record proves to be insufficient to tightly constrain carbon cycle processes or future feedback strength with implications for climate-carbon cycle model evaluation.”

    The Oceanic Sink for Anthropogenic CO2
    Science 305 (5682), 367 (2004)

    …”The current fraction of total anthropogenic CO2 emissions stored in the ocean appears to be about one-third of the long-term potential.”

    Comment by BarbieDoll Moment — 22 Feb 2007 @ 12:23 AM

  34. As a counter-assertion to some denialists’ assertion of solar forcing being way bigger than the graph shows, I’d like to assert that the forcings from CH4, N20 and Halocarbons are double what the graphs indicate, and that the forcing from CO2 is less than half that. I have said before that this would imply a big policy shift. Neither the cold case evidence or the CSI evidence seems to be able to disprove this assertion. Am I missing some critical scientific experiment here that would change my skeptical mind? I’m not sure of the author of that graph, but what makes them so confident about their CO2 vs CH4 forcings being accurate to within 20% of their ranges or so?

    [Response: The forcings by the greenhouse gases have little uncertainty because their concentrations are accurately measured in the atmosphere, and their infrared absorption properties are very accurately measured in the laboratory. The two are put together using highly accurate numerical methods that have little error. The small uncertainty is primarily because the radiative forcing depends on temperature profiles (well observed), water vapor profiles (somewhat less well observed) and cloud profiles (with additional uncertainties). The water vapor and clouds come in because you get little additional radiative forcing from greenhouse gas increases below a thick cloud. Similarly, water vapor competes somewhat with absorption due to the other greenhouse gases. There is no plausible ways these uncertainties could be stretched to accomodate the scenario you are proposing. –raypierre]

    Comment by Marco Parigi — 22 Feb 2007 @ 12:57 AM

  35. Raypierre (#32),

    If you want to see one aerosol expert’s view, look here.

    I happen to think it’s greatly exaggerated (in fact my views have strengthened since writing that post), but then he’s the one writing in Nature and I’m the one merely blogging about it :-)

    (If you follow the links you will find RC has also talked about it before.)

    [Response: All very good points to be reminded of, in the context of the present discussion. –raypierre]

    Comment by James Annan — 22 Feb 2007 @ 12:57 AM

  36. Thanks, everyone, for the interesting & informative discussion.

    There were several comments and questions about uncertainty (error bars in the figure) and the assigned “level of scientific understanding” for each forcing. The full description of how these were derived in the new IPCC 4AR will be published with the full Technical Summary later this spring, but I assume they will be essentially the same as in the predecessor 2001 IPCC TAR. In that case, the error bars on the radiative forcing plots represented the spread in published estimates of the forcing for each source. The subjectively assigned “level of scientific understanding” (LOSU) was defined in chapter 6 of the TAR as representing “our subjective judgement about the reliability of the forcing estimate, involving factors such as the assumptions necessary to evaluate the forcing, the degree of our knowledge of the physical/chemical mechanisms determining the forcing, and the uncertainties surrounding the quantitative estimate of the forcing.”
    So, to post #29: the LOSU don’t affect warming estimates at all.

    Re #17: yes, the solar irradiance forcing represents the change since 1750, as are all the forcings on this plot.

    Re #22 etc.: Thanks, Ray, for correcting my error on the CO2 lifetime. My apologies for perpetuating a misconception. I have, however, seen these “low” CO2 lifetimes thrown around a lot, presumably because as David Archer points out: “If one is forced to simplify reality into a single number for popular discussion, several hundred years is a sensible number to choose, because it tells three-quarters of the story, and the part of the story which applies to our own lifetimes.” (I put low in quotation marks, because I think 100 years would be plenty long enough to encourage some proactive public policy, if anything longer would) Some basics of why CO2 lifetime is effectively much longer than 100 years have been discussed in these comments by now, but for anyone interested in more detailed discussion, the full post from David Archer about CO2 lifetime, is here.

    Re #30: Uncertainty in aerosol forcing doesn’t directly imply uncertainty in other forcings, because there are additional constraints on those other forcings beyond just the last 250 years. For a nice discussion of climate senstivity, check out this post.

    Thanks, Ryan and others, for bringing up regional variability in aerosols. This is an incredibly important point, and one which I am certain will be addressed thoroughly in the technical summary portion of the IPCC report. So of course we shouldn’t make too much out of the globally averaged aerosol forcing.

    Comment by Juliane Fry — 22 Feb 2007 @ 1:31 AM

  37. Let me amplify on #37: here’s the other RealClimate link (that James’ blog point to) I should have put in my comment about climate sensitivity and how uncertainty in aerosols relates to future climate projection:
    thanks James.

    Comment by Juliane Fry — 22 Feb 2007 @ 1:37 AM

  38. This was a great primer on aerosols. In my never-ending quest to understanding climate science the one area I was almost clueless on was aerosols ;)

    On raypierre’s response to Philippe Chantreau #33, sometimes people who are trying to learn about climate science and who hear alot of information in the popular media and the internet don’t realize how much of the science is not controversial within the scientific community. Some of the facts are so well settled that you will not see them a journal paper. To find out about it you have to consult a basic science textbook

    Comment by Joseph O'Sullivan — 22 Feb 2007 @ 1:46 AM

  39. Sometime ago, I made a figure showing the removal of carbon dioxide from the atmosphere. A large chuck (70-85%) will be expected to be removed from the atmosphere after ~200 years, but in actuality it has just been transferred to the ocean and biosphere. Ultimately removing the excess carbon from the atmosphere-biosphere-ocean system occurs primarily through the production of carbonate rocks and may take 100s of thousands of years to fully occur.

    Incidentally, as a historically anecdote, the TAR said that carbon dioxide had a residence time of 5 to 200 years. This memorable statement is based on the Wigley 1991 carbon cycle model where ocean uptake was modeled as a sum of five processes. Four of those processes had lifetimes ranging from 5 to 200 years. However, the fifth process had a lifetime of infinity! Wigley’s model, which in that iteration was only intended to predict a few thousand years, actually used the approximation that 15% of carbon never left the atmosphere. This got rather muddled when the IPCC used the 5-200 numbers but didn’t effectively convey that there was an additional portion that essentially never dissipates (from the point of view of human time scales).

    Comment by Robert A. Rohde — 22 Feb 2007 @ 2:04 AM

  40. RE #18:

    It is staggering to consider that the error bar for the forcing caused by aerosols includes a negative number that is larger than even the highest number in the error bar for the positive forcing of GHGs.

    If I were a skeptic, this is clearly the fact I would harp on.

    Comment by Eric — 22 Feb 2007 @ 4:47 AM

  41. So the forcings of greenhouse gases would be greater if it was not for humans releasing counter chemicals which are often a product of burning coal in particular.

    Therefore if we moved to clean coal technology we might not release much carbon into the atmosphere but also aerosols will lessen and hence warming would take some time to lessen in fact it might even rise tempoarily. I am presuming that aerosols are responsible for some of the so called global dimming effect?

    [Response: For health reasons and acid rain reasons, you have to switch to clean(er) coal anyway. Even China is doing some of that already. If one insists on keeping aerosols in the atmosphere as part of the solution, one is going to need to put them there deliberately, and in a way that is less environmentally destructive than burning coal dirty. I myself doubt that it’s a viable solution, but people do talk about it. –raypierre]

    Comment by pete best — 22 Feb 2007 @ 5:58 AM

  42. One and all,–thank you, thank you, thank you for a sparkling discussion. Particularly, I thank Julianne Fry and Ray Pierre for bringing out the problem of conveying to lay folk like myself (who must take off their socks to count above ten) CO2’s life time. I say better a sudden and briefer rise in global heat with the shut-down of CO2 generators than with our Business As Usual. For psychologists it must be a puzzle that some of us understand compound interest in one context and not in another.

    Comment by Juola (Joe) A. Haga — 22 Feb 2007 @ 8:53 AM

  43. RE: 43 In Pollutant Removal Race, CO2 Beaten by S

    Although touched on in the introduction to this topic, it is important to clarify the difference between how easily and rapidly the sulfate aerosol precursors can be removed from fossil fuel sources vs. carbon from combustion sources or fuels.

    Technologies already exist and are being employed to desulfurize coal and petroleum, either pre- or post combustion. The issue there is how rapidly these removal technologies can be applied to, e.g., a new coal-fired power plant in China or a new refinery.

    There are no large-scale technologies for removing carbon or CO2 from these sources and probably won’t be for at least 20 years. Thus, it is more likely that the negative forcing from tropospheric aerosols will decline and become insignificant well before any significant removal of carbon or carbon dioxide takes place. Bottom line. Don’t count on that -1.2 or -1.5 W/m2 to help out after 2050 and expect to see it decline by several percent every year.

    Comment by Alvia Gaskill — 22 Feb 2007 @ 9:00 AM

  44. The relative lifetimes of CO2 and aerosol in the atmosphere result in the expectation that reducing fossil fuel use will accelerate warming. A CO2 molecule has a lifetime of about 100 years in the atmosphere, while an aerosol particle has an average life expectancy of only about 10 days. Therefore, if we instantaneously ceased using combustion engines, the (cooling) fossil fuel-related aerosols would be cleaned out of the atmosphere within weeks, while the (warming) CO2 would remain much longer, leaving a net positive forcing from the reduction in emissions for a century or more.

    How does the expected life time of an aerosol being 10 days square up against a half life of a volcanic erruption of a 1-1.5 years

    Hansen et al (1992).


    [Response: The difference is whether the aerosols are in the troposphere (the lower part of the atmosphere where all the ‘weather’ is), or higher up in the stratosphere. The main removal process for aerosols is related to rain and clouds, and up in the stratosphere there isn’t any to speak of. Thus once things get up there (for instance after a large volcanic erruption), they stay around for a lot longer. – gavin]

    Comment by Nick — 22 Feb 2007 @ 9:16 AM

  45. How is the LOSU determined? Is it based on the range of uncertainty re: forcing?

    Comment by Justin — 22 Feb 2007 @ 9:17 AM

  46. Please can you give us some responses, for the third or fourth time, about recent evolution of aerosols forcings (with links if possible) and concerning the definition of LOSU and its application to the quantification of aerosols forcing?
    If it is not possible, please, say it.

    Comment by Pascal — 22 Feb 2007 @ 10:00 AM

  47. Juliane-SO2 dissolves in water vapor to form H2SO3, sulfurous acid. Some of the sulfurous acid is subsequently oxidized to H2SO4, sulfuric acid. The sulfurous/sulfuric acid portion of the particles which we see as white haze is actually composed of tiny transparent spherical liquid droplets in the 0.01 to 10 micron diameter range.

    Transparent spherical bodies, including water, are retroreflective i.e. they reflect light directly back to the source of illumination. A common example is the glass beads used in highway signage and road stripes to send light back toward the headlights of approaching vehicles. I am sure this effect diminishes or disappears at some low diameter around the wavelength of light or about 0.7 microns for visible light.

    My question is: does the retroreflectivity of the larger droplets, i.e. back towards the light source, play into the sulfur aerosol/water droplet issue or is it simply averaged out by the bulk effect of all the aerosol particles present in the apparently white haze?

    Comment by Henry Molvar — 22 Feb 2007 @ 10:04 AM

  48. RE # 46 & 47: please see the 1st paragraph of my post #37 above. LOSU is a subjectively assigned label, which is NOT connected to uncertainty or quantitative estimates of forcing. Since the full 2007 IPCC 4AR isn’t out yet, you can look at the last report, (2001 IPCC TAR), chapter 6, for discussion of LOSU and uncertainty on the forcing plot. It can be found here.

    Comment by Juliane Fry — 22 Feb 2007 @ 11:11 AM

  49. Digression: whenever Danny Bee or some other name posts another link and linked name to that page
    climatechange3000 dot blogspotdot com
    (that’s the all-hopeless “Climate Change and the End of Humankind, Circa Year 2500” website) does that enhance their Google ranking credibility because it’s a link from

    Just asking.

    [Response: No, because I deleted it. To anyone else reading, attempted google bombing or commerical postings in comments are simply going to be removed. -gavin]

    Comment by Hank Roberts — 22 Feb 2007 @ 11:23 AM

  50. Oregon study showing increasing trend for direct normal solar irradiance. Decreasing cloud cover is blamed, but aerosols also mentioned.

    Comment by Gary — 22 Feb 2007 @ 11:42 AM

  51. Dr. Mann, that does have a comforting effect. Thanks.

    [Response: Mark, google searches on “Inhofe” or”Crichton” are similarly satisfying. Combinations are often even better, e.g. “Crichton” and “climate” or “Crichton” and “Inhofe” ;) -mike]

    Comment by Mark A. York — 22 Feb 2007 @ 12:09 PM

  52. Henry asked: “My question is: does the retroreflectivity of the larger droplets, i.e. back towards the light source, play into the sulfur aerosol/water droplet issue or is it simply averaged out by the bulk effect of all the aerosol particles present in the apparently white haze?”

    Not a climatologist speaking, but anecdotally — I suspect it mostly averages out and the light spreads in all directions, with some amount of reflection directly back toward the source. That’s from looking at the ‘Glory’ (circular rainbow around one’s shadow) and also from camping on mountains in thin cloud at night under a full moon and seeing absolutely no shadows at all, even under trees and inside tents; the moonlight spreads everywhere, scattered by the mist. It happens in daylight as well, though perhaps less magically. This effect was appreciated by the early photographers, working in Paris especially, as a way of getting even lighting for very long exposures required by early emulsions, I recall.

    Comment by Hank Roberts — 22 Feb 2007 @ 12:47 PM

  53. re#48

    thanks juliane

    Ok for this important (for me) confirmation of LOSU’s no-influence on uncertainty.
    I apologize for my insistance but for my question about the recent trend of aerosols forcing, can I hope a response?

    Comment by Pascal — 22 Feb 2007 @ 12:55 PM

  54. Re #41 response: ” If one insists on keeping aerosols in the atmosphere as part of the solution, one is going to need to put them there deliberately, and in a way that is less environmentally destructive than burning coal dirty.”

    I noticed an article in a recent Science News concerning the effects of a regional-scale nuclear war (using about 100 Hiroshima-size bombs). Seems as though the aerosols from that would nicely counteract AGW :-) Of course the problem is that you have to repeat every couple of decades…

    Comment by James — 22 Feb 2007 @ 1:02 PM

  55. #39 and others here have referred to the very long-term reduction of atmospheric CO2 (and de-acidification of sea water) via the production of carbonate rock. I haven’t seen anything detailing these processes and how they work. Where, for instance, do we find the carbonate-rock deposits which sequestered the CO2 which spiked during the PETM (55 mya)? Thanks for your help.

    Comment by Daniel Goodwin — 22 Feb 2007 @ 1:06 PM

  56. I have grave concerns regarding the likely introduction of massive amounts of SO2 and H2S over the next 50 – 100 years, as the huge native coal deposits in China are exploited. Take a boat ride on one of the many channels in the Pearl River Delta, and already, you will see coal piled up on the banks and being shuttled around on barges. It is burned both for direct heat for industrial processes as well as for power. If you want to see an amazing (and frightening) sight, along one of the southwestern channels, as you look out toward the west, you will see “the plain of stacks” – the most smokestacks I have ever seen in one view, anywhere on the planet.

    Add this on top of the growing dust quantity also coming from China, Mongolia, Eastern Russia and the Central Asian countries. All of it is stretching out across the North Pacific – and beyond!

    Comment by Steve Sadlov — 22 Feb 2007 @ 1:06 PM

  57. Great Post, THANK YOU

    I am concerned about one aspect of the figure reproduced from the IPCC AR4 SPM. It seems to be missing radiative forcing from black carbon, or the science has moved beyond these forcings. In recent analyses of climate forcings from Hansen and Sato as well as the IPCC TAR figures there are positive forcings assigned to black carbon (+0.39 W/sq m) from fossil fuel burning – this is in addition to the change in snow albedo on account of soot deposition of +0.17W/sq m. In addition the forcings show +0.11 and +0.08 W/sq m for the effect of soot from biomass burning on black carbon aerosols and deposition on snow respectively. Unfortunately, I don’t have the citation for the figure I am looking at [Figure 28. (a) a specific estimate fo climate forcings for 1750-2000, (b) same as (a) but the effective forcings partially sorted by sources.]

    Can someone tell me why they are not included in the AR4 SPM?

    [Response: They are. They are simply grouped in with the ‘Total Aerosol’ bars, except for the specific effect of black carbon on snow affecting the albedo (which is separated out). -gavin]

    Comment by Tom Huntington — 22 Feb 2007 @ 1:34 PM

  58. I think aerosols play a minor role in climate change since they can be controlled.

    Comment by Pephi Sondamase — 22 Feb 2007 @ 3:04 PM

  59. Re #52 and #30.

    What type of optics regime you are in depends on the ratio of the radiation’s wavelength to the object’s diamter. The interaction of solar wavelengths and atmospheric particles are primarily dictated by Mie Scattering, the most complicated type of light scattering (as opposed to geometric or Rayleigh). Mie scattering is highly directional, meaning that the scattering is not uniform in all directions from the particle. There is a strong angular dependence.
    For atmospheric radiation the Single Scattering Albedo (SSA) and Scattering Asymmettry Parameters are two important factors. SSA is the ratio of scattered light/light extinction (extinction = scattering + absorption). So a very refelective aerosol type (eg. ammonium sulphate) has an SSA ~ 1 while an absorbing aerosol (eg. soot) has an SSA ~0.3-0.4.
    The Scattering Asymmetry Parameter describes the angular dependence of the scattered light. In general, particles of a similar or larger diameter to the incident wavelength of light tend to mostly forward scatter light. Smaler particles tend to forward and backward scatter in roughly equal amounts.

    If you then consider that real particles in the atmosphere are not just complex mixtures but are also often not spherical (which is what Mie theory is for), then it gets really complicated.

    Note that I’m not really an expert of atmospheric radiation though. A good resource is “A First Course in Atmospheric Radiation” by Grant W. Petty.

    As for the sensitivites of light scattering for CO2 versus typical aerosol components, I’m not sure but this is a very good question. Usually “mass extinction/absorption coefficients” are reported for different types of aerosols to describe this. While aerosol composition is usually measured and reported on a mass basis (with some particle size segregation as well), the optical properties of an aerosol really depend on it size distribution (i.e. number concentration as a fucntion of particle size).

    Comment by Ryan Sullivan — 22 Feb 2007 @ 3:14 PM

  60. Re #56: I recently read a very interesting article about the huge amounts of GHGs released from coal mine fires (which I guess are pretty common). This would also release a lot of particulate matter, though I don’t think anyone has studied or directly measured those, yet.

    The article:

    “The CO2 production of all of these fires in China is more than the total CO2 production in The Netherlands,” Rosema says. This amounts to 2-3% of the annual worldwide production of CO 2 from fossil fuels, or as much as emitted from all of the cars and light trucks in the United States. “

    Comment by Ryan Sullivan — 22 Feb 2007 @ 3:21 PM

  61. RE 18: “Aerosols have a net radiative forcing of -1.2 W/m2 against a CO2 forcing of 1.66 W/m2. If I were an AGW convictee, the closeness of these figures along with the uncertainty regarding aerosols would concern me.” and 40: “It is staggering to consider that the error bar for the forcing caused by aerosols includes a negative number that is larger than even the highest number in the error bar for the positive forcing of GHGs. If I were a skeptic, this is clearly the fact I would harp on.”

    Enough with the hypotheticals, people, what is your point? I don’t care what you would harp on if you were (heaven forbid) a sceptic. What do *you* conclude from the large uncertainty in aerosol forcing?

    It is my understanding of that if the total aerosol forcing (direct plus cloud albedo) were really at the far negative end of their plausible range, i.e. -2.7 rather than -1.2 W/m2, then the total net anthropogenic forcing would have to be near at the bottom end of its plausible range, i.e. 0.6 rather than 1.6 W/m2. To reconcile this with the observed anthropogenic warming would require large climate sensitivity. But we know that the climate sensitivity is round about 3 degC (expressed as equilibrium sensitivity to a doubling of CO2) and James Annan has argued convincingly (to me at any rate) that it can’t be much higher. So large negative aeorosol forcings are excluded by other evidence.

    N’est-ce pas?

    Comment by Mark Hadfield — 22 Feb 2007 @ 3:42 PM

  62. Sorry, but I have a kooky question: Would there be any benefit to understanding aerosol forcings, etc, by having one day per year in which commercial flights aren’t scheduled in the US or world for 12 or 24 hours? I was originally thinking about something similar to “don’t drive your car to work day” for airplanes (because they burn a lot of carbon and because they’re easier to regulate than cars), but then I thought back to global dimming and a documentary in which a guy found the sky very clear after 9/11 (I think this RC posting talks about it Anyway, I wonder if such an annual experiment (say on 9/11 or Earth Day) would help climatologists.

    [Response: Well, the contrail effect is so small it’s hard to be conclusive on the basis of that. What would be a really lovely experiment would be to shut down all coal burning worldwide for about 10 days. If this were done at a time when there was good satellite coverage from sats that can measure aerosol properties, the results would be extremely valuable. I read that China will shut down a lot of industry near Beijjing for the Olympics. Maybe something could be done with that, looking on a regional scale. Good idea! –raypierre]

    Comment by Steve Latham — 22 Feb 2007 @ 4:23 PM

  63. I think all this discussion is fine longterm , but overloooks that the world is already in BIG trouble in many places and few people seem to be aware that the CO2 already there is gonna have consequences , let alone what we add to it because one cannot stop the way men do things very quickly [if at all until the fail!]…

    Thus we NEED to buy some time even for this elegant discussion else it becomes moot … the machines are already in the design phase to put [mostly salt] sea-water crystals into the clouds in the Southern Ocean to increase reflectance in a manner similar to that used by nature in aerosols generated from the peaks of waves in storms…

    The point is that it is really already too late and we need to use our existing knowledge , however slight, in controlled manner [with monitoring and review of results] to DO something NOW , immediately, as a matter of life-threatening urgency .

    IF everyone was simply informed and went out at weekends to plant a tree [willows are easy to grow] or some food plants, or anything green , one every scrap of soil or in pots or on roofs [sedum is good on roofs]then we should at least be STARTING the enormous task instead of making it worse by continuing OUR way of life …

    Equally we could bombard our sluuggish governments with petitions proving that the people DO want this problem solved and NEED leadership now, not the dithering inaction we see … only governments stand in the way of industry getting going on CO2 injection into porous ocean rocks [where under pressure the CO2 is dense enough not to ever escape]

    There are colossal tasks of changing feedstocks for industry that should be tackled before the oil gets more expensive and could in principle provide the review necessary of efficiency and recycling in all industrial processes.

    Even new houses are not being built to take account of what we know about the future which is absurd waste of resources adding to future burdens in changing infrastructure

    Our seas lack but relatively tiny ammounts of micronutriments [notably iron for phytoplankton enzyme systems] to becaome able to absorb massive ammounts of CO2 quite naturally and so boost fisheries that we choose mostly to meaninglessly deplete by over-fishing] and turn the excess CO2 into FOOD for humans … nature just needs a tiny ammount of help to let the ‘sea deserts’ bloom into a partial solution to world food shortages in many places, which simply must now increase unless we act now…

    The point is not that we don’t need to know about better aerosol reflectance, but that we need to start NOW with something ocs’ in many ways it is already to late to be starting and we need an all-out emergency response by everyone, today , not tomorrow…

    We have to use what we have and develop it as we go because elsewise there is no means to do someting better tomorrow [our civilisations could so easily fail as things go wrong in agriculture , the seas are already dying from CO2 acidification and it will kill the whole food chains with us at the end]

    Hoping that the greater storms due to climate chaos will put more salt aerosol up in the clouds and solve the problem just ain’t enough to justify not sitting around any more, but doing something positive to reverse the trends IN ONE’S OWN LIFE before sitting down again to see if one can find an even better way of helping the earth for everyone…

    people really are dying in increasing numbers already, the problem is here and now and bigger than any crisis man has ever faced before, bigger than world war… if it were war then people would take it seriously and mobilise with what they have , what they know, but this crisis is one we are buying for our future, it is more insidious than war… but it really needed action yesterday, so it is time to act to do something to remedy the situation, the time for talking comes after one has put in place all the actions one can in one’s own life… in every aspect of it … then begins the task of educating everyone else in the world … and only when one has finished that is it time to devise a better solution because one has bought the time in which to do so…

    Comment by Roger William Chamberlin — 22 Feb 2007 @ 4:32 PM

  64. It sort of occurred to me that our emissions (GHGs + aerosol = long-term warming, off-set a bit by some short-term cooling) are sort of like a “balloon” morrtgage in which a family pays well below even the interest due for a number of years, then the monthly payment greatly jumps up to pay off that unpaid innterest (plus principle), which is well beyond what a family would have had to pay had they gotten a fixed morrtage. This may not a good idea if you plan to retire by that time, keep that house, & live on less income. And a very bad idea if your house is in hurricane alley.

    The problem with this analogy is that there are also harms from the aerosols, such as acid rain (and to some extent sulfur dioxide) corroding forests, lakes, soil, property, and lungs. It would be interesting to figure if the aerosols lead to net good from cooling WHILE in the atmosphere or net harm, considering these other harms — which would be of a longer time duration.

    I’d think the fact that CO2 emissions by their extreme longevity in the atmosphere, are even more harmful than many are estimating (since most reports only go up to 2100, and it’s hard to estimate harms 10,000 years from now). But from a false-negative avoiding perspective, the situation looks very very bad. We should be thinking how much harm today’s emissions will cause over their lifetime in the atmosphere (or in carbolic acid in the ocean), plus the aerosol harms (& slight benefits). The whole picture over the life-time of harms & benefits. Even though it would be near-impossible to quantify.

    Comment by Lynn Vincentnathan — 22 Feb 2007 @ 4:59 PM

  65. > China will shut down a lot of industry near
    > Beijjing for the Olympics. Maybe something
    > could be done with that, looking on a regional
    > scale. Good idea! –raypierre]

    Great idea. If it’s possible to plan ahead by lining up satellite time and also to enlist local monitors around the various pollution sources that are in theory being shut down, to detect cheating site by site (like nighttime smoke), that’d give a very good source data set. I smell PhD material, if there are students there now who’d be able to start collecting baseline data in advance and continue afterward.

    Comment by Hank Roberts — 22 Feb 2007 @ 5:29 PM

  66. Re # 65: Of course, the same experiment will basically be done in the opposite direction as China builds numerous new coal plants in the next while.

    Comment by Steve Latham — 22 Feb 2007 @ 6:33 PM

  67. Where I live large amounts of wood are used for warming houses. The wood burning stoves are very efficient and burn hot giving off little smoke once they get going.The wood is sustainable being off cuts from timber yards and plantations and from fallen trees. It has been found to be the most economical as well. Where are the problems with this compared with burning oil or gas for heating or generating electricity from coal.

    Comment by Terry — 22 Feb 2007 @ 7:08 PM

  68. Gavin,

    So aerosols from a volcano go high into the atmosphere, and so take a long time to settle out.

    Ditto for aircraft.

    The graph and the article talk about aerosols, and not specifically anthropogenic aerosols.

    What’s the break down, because that needs to be clear.

    What is the expected life span of the different components, because it looks like the 10 days is selective picking just aerosols that are just low level.


    Comment by Nick — 22 Feb 2007 @ 8:32 PM

  69. Re #68: Nick — The latest super-eruption of Mt. Toba, about 74,000 years ago, resulted in sulfates(?) in the stratosphere which persisted for 3–6 years.

    Comment by David B. Benson — 22 Feb 2007 @ 9:19 PM

  70. Completely off topic:

    This press release shows U.S. internet searches for “global warming” hit .01% of the total for the four week period ending February 18. This is actually a very high number for a specific issue (noting that it doesn’t include terms like “climate change,” “climate warming” or “climate science”) and reflects a huge increase over a year ago. RC is not in the list of top sites, but I suspect benefited since it’s prominently linked by many of the ones that are (many of which didn’t even exist until recently). What’s most gratifying is that there isn’t a single denialist site on that list (which is confirmed by a current google search, in which the first denialist site doesn’t show up until the middle of page four). RC co-author William Connolley, who has taken special charge of making sure the Wikipedia climate pages are accurate, will be particularly pleased since WP got the most hits of all (14.5% of the total).

    The press release includes an interestingly-shaped graph that may arouse a feeling of irony in some.

    Comment by Steve Bloom — 22 Feb 2007 @ 9:26 PM

  71. Enough with the hypotheticals, people, what is your point? I don’t care what you would harp on if you were (heaven forbid) a sceptic. What do *you* conclude from the large uncertainty in aerosol forcing?

    I still conclude that scientists are being unskeptically selective in how they are calculating uncertainties. To me the observable quantities are the measured temperature increase in 200 years correlated with increases in all these “suspects”. I believe this correlation gives us the confidence to say how much the overall effect is because it is based on actual temperature measurements. In a sense, the total forcing is calibrated to actual data for this planet. Meanwhile, the calculations based on the physical properties and measured concentrations do not have this same directly observable calibration. There may be other effects associated with exactly the same compounds (or different compounds) that are just not observable directly because of the cross-correlation, and the models have only coincidentally matched due to manmade things generally rising in unison.

    Comment by Marco Parigi — 22 Feb 2007 @ 9:51 PM

  72. re: 63 … to DO something NOW , immediately, as a matter of life-threatening urgency. …

    There are many eminent scientists saying about the same thing as you did.

    “The pace of change and the evidence of harm have increased markedly over the last five years. The time to control greenhouse gas emissions is now.”

    “These events are early warning signs of even more devastating damage to come, some of which will be irreversible,” warned the board.

    Comment by pat neuman — 22 Feb 2007 @ 9:52 PM

  73. Thanks for the tip on CO2 absorbtion’s spectrum. I have basic and patchy science background so this is challenging for me but this site is definitely outstanding!

    Comment by Philippe Chantreau — 22 Feb 2007 @ 10:27 PM

  74. Since we are facing the problem of regional drought, the effect of aerosols on regional precipitation should be considered. A recent AGU paper found that aerosols decreased precipitation over east Asia. “Direct and indirect effects of anthropogenic aerosols on regional precipitation over east Asia” Jour. of Geophysical Research, v.112, D03212, doi:10.1029/2006JD007114,2007

    Comment by Richard LaRosa — 22 Feb 2007 @ 11:08 PM

  75. I have heard a claim that the planet would be 60-70 degrees F cooler if green house gases were removed (leaving oxygen and nitrogen). As CO2 is the dominant greenhouse gas, most of the greenhouse effect appears to be related to this one gas, directly or indirectly (H20 into air). I bring this up because establishing CO2 as essential in making the Earth habitable implicitly gets one half way to addressing most skeptic arguments (with the public at least).

    Comment by Daniel Morris — 22 Feb 2007 @ 11:17 PM

  76. Re #71: Marco, that reasoning is the purest of handwaving. Recall that the behavior of the various atmospheric constituents has been of great interest for many years prior to concern being expressed about global warming, and nothing like what you speculate about has been found. Your idea that the observed behavior of GHGs would just disappear in the atmosphere seems especially fanciful.

    Comment by Steve Bloom — 22 Feb 2007 @ 11:36 PM

  77. Re: reply to #34 There is no plausible ways these uncertainties could be stretched to accomodate the scenario you are proposing. –raypierre]

    Firstly, I’d like to thank raypierre for taking the time to respond personally to my assertion. It seems that you are talking about uncertainties in the numerical models putting everything that is known to be uncertain. One more recent uncertainty of CH4, ie the stratospheric water vapour has been listed separately there and I thought some scientists had asserted it to be far higher than your graph shows. Some of these substances can also be catalysts, set off positive or negative feedbacks, that could be quite significant but as yet unobserved or attributed incorrectly. Has some form of regression analysis been performed regionally to tease out these separate forcings from actual data rather than forcings calculated from first principles?

    Comment by Marco Parigi — 23 Feb 2007 @ 1:57 AM

  78. Re: #13

    ” And because aerosols are often so short lived and so spatially
    inhomogenous,” ….

    …. wouldn’t we expect the indusrialised nations in the Northern
    Hemisphere to be cooling (or warming at a lower rate) than those in
    the SH. i.e. the exact opposite to what is actually happening

    [Response: … if every thing else was equal, sure. But it’s not. Principally the amount of land in the Northern Hemisphere is much greater than in the South, and since land has a much quicker response (less heat capacity than deep oceans), it warms faster. That turns out to be a significantly stronger effect. -gavin]

    Comment by Caz — 23 Feb 2007 @ 6:05 AM

  79. [[Why do I never hear that the CO2 greenhouse effect is saturated ?]]

    Because it isn’t. When the line center is saturated, there is still absorption in the wings. You might want to look up how line shapes are calculated and observed. Goody and Yung’s “Atmospheric Radiation” (1989) is a good source, but some of it can also be found in Houghton’s “The Physics of Atmospheres” (2002).

    [Response: What’s more, even for a grey gas where absorption is independent of wavelength, the greenhouse effect would never saturate no matter how much you put in. The reason is that the greenhouse effect arises from the fact that adding a greenhouse gas moves the altitude from which radiation escapes to higher levels, where temperature is lower. Since radiation goes down like the fourth power of temperature, that makes the radiation to space lower (for fixed surface temperature). As long as there is some colder air up there, adding more greenhouse gas makes more greenhouse effect. It doesn’t even need unsaturated bands (though for CO2 these do indeed help). One thing that makes cold air aloft is convection, which lifts and cools air. However, as you add more greenhouse gas, that cools the stratosphere, making even more cold air available. This is all explained in Chapter 4 of my ClimateBook. The lack of saturation of greenhouse effect is how you can make Venus have a surface temperature of 740K. You’d never get that hot if you ran out of greenhouse effect at the piddling few hundred parts per million we have on Earth. –raypierre]

    Comment by Barton Paul Levenson — 23 Feb 2007 @ 8:05 AM

  80. [[Wow. “aerosols remain the least understood component of the climate system.”
    Aerosols have a net radiative forcing of -1.2 W/m2 against a CO2 forcing of 1.66 W/m2. If I were an AGW convictee, the closeness of these figures along with the uncertainty regarding aerosols would concern me. ]]

    The feedback from water vapor and ice/albedo, and the warming from other greenhouse gases such as methane, nitrous oxide, and ozone, makes the warming component a lot larger than 1.66 W/m2. There’s no question that the warming dominates over the cooling.

    [Response: Actually, the feedbacks aren’t relevant for this comparison, but all the other forcings obviously are. As you say, there is very little possibilty that the net forcing is negative. -gavin]

    Comment by Barton Paul Levenson — 23 Feb 2007 @ 8:08 AM

  81. “A CO2 molecule has a lifetime of about 100 years in the atmosphere, while an aerosol particle has an average life expectancy of only about 10 days. Therefore, if we instantaneously ceased using combustion engines, the (cooling) fossil fuel-related aerosols would be cleaned out of the atmosphere within weeks, while the (warming) CO2 would remain much longer, leaving a net positive forcing from the reduction in emissions for a century or more.”

    Despite all the comments, I’m still having trouble understanding exactly what Juliane is asserting here, and on what basis. Is it:
    1) If we stopped all fossil fuel use now [and everything else continued unchanged], it will be more than a century before the reduction in enhanced greenhouse effect due to the CO2 from post-1750 fossil fuel use leaving the atmosphere outweighs the reduction in reflection of solar irradiation due to the aerosols from fossil fuel use leaving the atmosphere.
    2) If we stopped all fossil fuel use now [and everything else continued unchanged], it will be more than a century before net positive forcing falls below the level that would result if we continued using the same amount of fossil fuel in the same way as now.
    3) If we stopped all fossil fuel use now, it will be more than a century before net positive forcing falls below the level that would result if we continued using fossil fuel on a “business as usual” path.
    4) Something else?
    Whichever is being asserted, can the supporting calculations be summarised here, or accessed elsewhere?

    Comment by Nick Gotts — 23 Feb 2007 @ 8:20 AM

  82. [[I believe this correlation gives us the confidence to say how much the overall effect is because it is based on actual temperature measurements. In a sense, the total forcing is calibrated to actual data for this planet. ]]

    CO2 radiative forcing is NOT based on empirical measurements. It is calculated from the known properties of CO2 and the amount of CO2 in the atmosphere. It won’t change with new data. We’ve known about thousands of CO2 lines for decades and the calculations, while intricate, are straightforward.

    Comment by Barton Paul Levenson — 23 Feb 2007 @ 8:30 AM

  83. [[I have heard a claim that the planet would be 60-70 degrees F cooler if green house gases were removed (leaving oxygen and nitrogen). As CO2 is the dominant greenhouse gas, most of the greenhouse effect appears to be related to this one gas, directly or indirectly (H20 into air). I bring this up because establishing CO2 as essential in making the Earth habitable implicitly gets one half way to addressing most skeptic arguments (with the public at least). ]]

    Most of the 33 K greenhouse warming on Earth is caused by water vapor. It’s not really possible to break it down by individual agents, but without being too far off you might make it 21 K from H2O and clouds, 7 K from CO2 and 5 K from other greenhouse gases.

    Comment by Barton Paul Levenson — 23 Feb 2007 @ 8:37 AM

  84. [[Why do I never hear that the CO2 greenhouse effect is saturated ?]]

    It seems to me that the denials want to have it both ways. Sometimes they say it’s prepposterous to think that the tiny ppm of CO2 could have any effect at all, and the tiny additions to this from humans, even less possibility of an effect. Then you hear there’s too much CO2 up there to have any effect, just too crowded.

    Seems to me that the 1st case is correct in pointing out that these molecules are really spread thin — with the fantastic, counter-intuitive fact that they do help warm the earth. AND seems there’s plenty of more room up there for more of them….

    Comment by Lynn Vincentnathan — 23 Feb 2007 @ 9:12 AM

  85. Re 80 (BPL) and other comments.
    The IPCC Summary for Policymakers – that which is regularly claimed to represent the ‘scientific concensus’ demonstrates (on the basis of current knowledge) that it is perfectly feasible that negative forcing components outweigh the positive forcing component of CO2. CO2 could be 1.49, and aerosols could be -2.7.
    We so often hear that ‘the science is settled’, that ‘there is no room for doubt’, etc. You can add up all the postivie forcings, but what these statements assume is that manmade CO2 emissions are causing AGW. The IPCC Summary for Policymakers itself demonstrates this is far from being a certainty.
    It is clear I am a ‘skeptic’ (‘denialist’ is a naive and immature term for those with their head firmly in the sand – or is it the clouds?). Most with a view on this subject already have relatively firm views, so I don’t expect to change these. My principle concern is that it must be accepted that the debate continues.
    Personally, I strongly believe in protecting the environment and maintaining a sustainable world. To always accuse ‘skeptics’ as being ‘in the pay of the fossil fuel industry’ is a nonscense (some are, but many are not). What I can never accept is the distortion of the scientific process. By this, I do not mean the belief in AGW – which is an acceptable point of view (if based on judgement and not faith) – but what I include is the ridiculous claim that ‘the science is settled’ and that it is impossible to believe otherwise unless you have some ulterior motive.
    My reassurance is that this site only exists because the debate exists.

    Comment by PHE — 23 Feb 2007 @ 6:46 PM

  86. a clarification (maybe I’ll find it later, but don’t want to forget):

    [[While a relatively minor part of the overall aerosol mass, changes in the anthropogenic portion of aerosols since 1750 have resulted in a globally averaged net radiative forcing of roughly -1.2 W/m2,…]]

    Is -1.2W/m2 currently? what does “global average since 1750” mean?

    Is the -1.2 W/m2 only from anthropgenic aerosols? What do the (relatively much greater??) natural (?) aerosols do? The graph shows
    -1.2 W/m2 total aerosol forcing. Can someone straighten me out?

    Comment by Rod B. — 23 Feb 2007 @ 10:37 PM

  87. Re #81: Let me attempt a crude calculation of how long it takes before a reduction in fossil fuel use lead to cooling. I will start by assuming all aerosols and carbon dioxide come from fossil fuel burning (in reality it is only part of both, so maybe the errors roughly cancel). According to figure SPM-2 from the recent IPCC Summary for Policy Makers, stopping fossil fuel use would result in an immediate increase in forcing of 1.2 watts per square meter (W/m2), the sum of the two aerosol forcings. The present forcing from carbon dioxide is 1.7 W/m2. Assuming the relationship between CO2 concentration and forcing is linear (not true: it is logarithmic, each unit of decrease will have more effect, but that is good enough for this crude calculation) we need to get rid of 70% of the CO2 to remove 1.2 W/m2 of forcing.

    Reading from the CO2 decay rate from this page, it will indeed take one hundred years to reduce CO2 by 70%. However the result is very sensitive – if we assume we only need a 50% CO2 reduction (because of the large uncertainty in aerosol forcing or other problems with the figures I use), the time is reduced to 20 years.

    Even the more optimistic result indicates we get net warming for 20 years after reducing fossil fuel use. I wonder how many people are really aware of the long time scales involved in this issue. There are no quick fixes. This is not a justification for doing nothing, but we must be realistic.

    I would love to see a better calculation than this one.

    Comment by Blair Dowden — 23 Feb 2007 @ 11:08 PM

  88. My understanding is that aerosol emissions from fossil fuel burning are likely to be heavily reduced regardless of what happens to CO2 emissions. Smog is very noxious and countries like China are likely to seriously reign it in soon (my guess is within a few years – they probably would have tackled it earlier if it weren’t for the chronic electricity shortages). The developed world has been quite successfully tackling smog for decades and gross emissions have been dropping.

    Comment by yartrebo — 24 Feb 2007 @ 12:54 AM

  89. In order to estimate the forcing of aerosols, we need a good microphysics of each kind of particles, but also, more basically, a quantification of these particles (like we’ve with GHGs atmospheric concentrations) and a quantification of natural particles (to assess the relative role of anthropic ones in their indirect effects). Do we have such estimates at a global scale? Does uncertainty deal with a low physical understanding or just with a difficulty to count up?

    Comment by Charles Muller — 24 Feb 2007 @ 5:59 AM

  90. Some time ago that I have commented here. As a lukewarm skeptic (I am sure that more CO2 causes some warming, but I am far from convinced that we are heading to a catastrophic warming), I have reacted several times on this forum about aerosol forcing and its effects.

    To begin with, there is an offset in response between aerosol cooling and GHG warming. If (anthro) aerosols have a huge influence, then the sensitivity for GHGs is high, if aerosols have a low influence, then GHGs have a low influence too. This is reflected in the first graph of the RC discussion about climate sensitivity and aerosols, and has huge consequences for projecting the future.

    There are several indications that anthropogenic aerosols have a small influence on climate.

    – While SO2 emissions (which give the strongest cooling) are nearly constant since about 1975, there is a huge shift in regional sources. Europe (and North America) have made huge reductions, while SE Asia firmly increased. One should see a huge change in temperature trends within Europe between less polluted and more polluted areas in the main wind direction, but these are not measurable.

    – Aerosol models underestimate natural aerosols. One measurement off the coast of West Africa found about 90% salt spray, while the model calculated 50% anthro (sorry, lost the reference). Another investigation found that the load of natural (SOA – VOC induced secondary oxydised) aerosols in the free troposphere was underestimated with a factor 2-100 in chemical transport models (see Heald ea.).
    The mass ratio SOA/SOx (SO2+sulfate) aerosol is app. 2:1 to >10:1, between 0.5 and 5.5 km altitude. These are natural fine aerosols with similar properties as sulfate aerosols.

    – About 90% of anthro SO2 is emitted in the NH. Very little of this passes the equator, thus the influence must be maximal in the NH. This is not reflected in the temperature trends, as the NH warms faster than the SH. Not only because there is more land in the NH (which indeed warms faster), but also the heat content of the NH oceans increases substantially faster than the SH oceans, if corrected for area. This points to a more positive W/m2 radiation balance for the NH than for the SH.
    If we accept the forcings as reflected in the SPM, then GHGs forcing is evenly distributed over the NH and SH (overall about 3 W/m2). But as 90% of the anthro aerosols are emitted in the NH, this would give some -2.2 W/m2 cooling from aerosols in the NH, against -0.2 W/m2 in the SH with a global average of -1.2 W/m2. That means that the NH should have an overall radiation balance of +0.8 W/m2 (all forcings included) since 1850, and should be warming far less rapidely than the SH with about +2.8 W/m2.
    As the NH is warming more rapidely than the SH, this -again- points to a low influence of aerosols and consequently a low climate sensitivity for GHGs…

    Comment by Ferdinand Engelbeen — 24 Feb 2007 @ 6:08 AM

  91. #90 Please to read you, Ferdinand.

    I’m still skeptic about conclusions concerning aerosols forcing evaluation (either high or low). Some works on recent trends (better known that 1750-2000 means) suggest their effects could be important, after all.

    If we accept the global dimming / brightening transition measured by GEBA / BSRN stations as a physical reality rather than a statistical artifact (Pallé 2005 ; Wild 2005, 2007), and if we consider these trends over lands are mainly driven by anthropic aerosol emissions (Streets 2006), you have a slight warming (for Tmin, cooling for Tmax) between 1960-85, and a strong warming (Tmin and Tmax) between 1985-2002. Doesn’t it plead in favour of an important negative aerosol forcing ?

    One can look at the interesting paper of Wild et al. 2007 (they conclude that the recent increase of T cannot be attributed to surface insolation trends 1960-2000, at least on GEBA network, because surface insolation 2000 is still under the 1960 level, in spite of downward aerosol emissions over industrialized countries) :

    GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L04702, doi:10.1029/2006GL028031, 2007
    Impact of global dimming and brightening on global warming
    Martin Wild, Atsumu Ohmura, Knut Makowski

    Comment by Charles Muller — 24 Feb 2007 @ 11:05 AM

  92. Re #91,

    Charles, I beg to differ about the role that anthro aerosols play in global dimming. I have not (yet) read the 2007 Wild ea. paper, but had some discussion on global dimming in the past here (comments #23 and #25):

    About the suggestion that aerosols may be involved: Although the emissions in Western Europe have sharply declined (over 50% since 1975), the timing doesn’t correspond to the decrease in insolation until 1990 and the recovery thereafter. Neither does that correspond to the increase in solar radiation in Australia and Antarctica since 1990, where human made aerosols have no measurable impact. Moreover, the global emission of sulfate aerosols is near steady since 1975, but with a large shift from Europe (and North America) toward SE Asia. This may be seen in the data of India, but China with an explosively increasing industry shows increasing insolation…

    I don’t think that aerosol emissions in China currently are lower than in the 1990s.

    Thus the main problem with the aerosol-dimming connection is that the timing of regional/global emission trends and regional/global dimming trends don’t match.

    As said in comment #25 of the above RC link, it seems that clouds and water vapor (especially in Europe) are mainly responsible for global dimming and brightening…
    Btw, the first link in comment #25 doesn’t work anymore. It was referring to the (free copy) work of Philipona and Durr, “Greenhouse forcing outweighs decreasing solar radiation driving rapid temperature rise over land”, GRL, VOL. 31, L22208, 2004, now only available for a fee. The “greenhouse forcing” in that article seems to be mainly from increased water vapor (probably NAO induced…).

    Comment by Ferdinand Engelbeen — 24 Feb 2007 @ 3:11 PM

  93. When someone who can follow the science gets the full text of Wild and has time to read it, please comment. It’s an interesting abstract.

    Comment by Hank Roberts — 24 Feb 2007 @ 4:16 PM

  94. RE: #75 and 83

    Dear Mr. Levenson,

    I am fully aware that water functions as the dominant greenhouse gas. I am not trying to break out the individual contributions. The question is whether the absence of CO2 and methane would also reduce the concentration of water to the extent that surface temperature would drop about 60 degrees F.

    Perhaps I should indicate the number came from an article by Immanuel Kerry:

    [Response: That’s Kerry Emanuel. If the Earth had a pure Nitrogen or a Nitrogen/Oxygen atmosphere, having no greenhouse effect, the temperature would be about 255 Kelvin — if the Earth had no oceans to freeze over. The actual mean temperature is more like 285K, so the net greenhouse effect (neglecting ice-albedo feedback) is more like 30K (which is also 30C). Now, since we have oceans that would freeze, the fact is that without the greenhouse effect the oceans would freeze over, increasing the reflectivity of the planet. That drops the temperature to 230K or less. That would say the greenhouse warming is something over 60C. For more details see Chapter 3 of my ClimateBook –raypierre]

    Comment by Daniel Morris — 24 Feb 2007 @ 9:20 PM

  95. Article by Kerry Emanuel:

    “Air is …composed almost entirely of oxygen and nitrogen, …. Such molecules barely interact with radiation….. If that is all there were to the atmosphere, … the average temperature of the earth’s surface …. Accounting for the amount of sunlight reflected back to space by the planet ….. works out to be about 0°F, far cooler than the observed mean surface temperature of about 60°F.”

    Raypierre has written about science fiction atmospheres; he probably knows if it’d be possible to change only to zero CO2 and keep the planet warm enough not to freeze out the water, but that’d be a slippery slope to a snowball planet, I imagine.

    Comment by Hank Roberts — 24 Feb 2007 @ 10:25 PM

  96. It sort of occurred to me that with more water vapour in the air under GW conditions, there is a greater chance for SO2 & NOx to become sulfuric acid and nitric acid (I don’t know if my chemicals are correct, but you know what I mean), at least in contexts where areas of increased WV & SO2 & NOx converge. Could this be another negative effect of GW???

    Comment by Lynn Vincentnathan — 24 Feb 2007 @ 10:56 PM

  97. Regarding the issue of residence times, it seems a bit hard to apply to CO2 in the current environment. See the description of residence time calculation at: The steady-state assumption is off, since CO2 in the atmosphere is currently increasing at something like 2.0 ppm/year (and accelerating). We also know that only half the CO2 emitted by human activity stays in the atmosphere, and then you have the biosphere’s photosynthesis and respiration. The biosphere flux to the atmosphere is >100 in, 100 out, while the human flux is 6 in, 3 out. (GtC) The biosphere appears to operate in steady state, unless there is organic carbon burial going on (fossil fuel formation) or land-use changes (deforestation). Trying to figure out the residence time of methane is even worse, since that’s largely determined by atmospheric chemistry (which ends up converting CH4 to CO2 – another flux term). The oceans have 50x as much dissolved inorganic carbon as the atmosphere, but the mixing time is slow (slowing?)…there’s a good site on all this at (Maybe the pre-industrial residence time of CO2 is well-defined, however)

    This all relates to the potential carbon cycle-feedback responses, which were briefly mentioned in the fourth IPCC summary. There aren’t any climate models that I’ve heard of that include CO2 cycle effects, but it’d be ridiculously difficult because you’d have to include photosynthesis and respiration (and human behavior!). However, perhaps the IPCC should include emissions scenarios for both strong and weak CO2 feedback effects.

    Regarding aerosol measurements, there are airborne mass spectrometers that can get this data; for example see J. Schneider et al 2003 Aerosol Sampling (pdf) which mostly shows that tropospheric aerosols are highly variable between regions and even in the morning vs. the evening. Trying to directly measure the indirect aerosol cloud effect? That seems difficult.

    Regarding the Wild paper on aerosols and global dimming, a brief synopsis from Science is available at . It seems clear that aerosols from volcanoes can have a significant effect; see “Significant decadal-scale impact of volcanic eruptions on sea level and ocean heat content” Church 2005 (abstract). (Incidentally, inducing short-term cooling by setting off volcanoes with nuclear weapons is a bad idea, for many reasons, but is on par with the other geoengineering proposals).

    Thanks for the clear discussion of this complex topic.

    Comment by Ike Solem — 25 Feb 2007 @ 1:25 AM

  98. At a meeting last Friday our group at the University of Edinburgh discussed a recent EOS article by Gerald Stanhill on Global Dimming and Brightening (see this link).

    The reduction in solar radiation at the Earth’s surface he cites for the period 1958 to 1992 is huge: 20 W/m2. We just could not reconcile this with measured changes in global surface temperature during this period, or with the ‘global brightening’ reported since 1992. Can anyone explain why such an apparently huge change in solar radiation has not dominated the surface temperature signal? Compared to anthropogenic forcing over this period (around 2.5 W/m2) the global dimming/brightening story would seem to be very important. Stanhill seems to believe that AR4 has overlooked this issue, but I’m not familiar enough with the relevant literature on this to know if it’s really as important as it appears to be.

    Thanks in advance.

    Dr Dave Reay
    University of Edinburgh
    Recent books: Climate Change Begins at Home (Macmillan) and Greenhouse Gas Sinks (CABI)

    [Response: There are (at least) two problems with Stanhill’s analysis. First, he confuses the surface forcing with the radiative forcing from CO2 (defined at the tropopause). The former, while interesting, does not imply very much about the latter (which is what the global temperature generally responds to). We have a paper in press that shows clearly that ‘global dimming’ and ‘global warming’ are not mutually exclusive concepts. Secondly, his estimate of 20 W/m2 for the surface forcing in no way can be described as a ‘global’ average. This has been discussed here previously: . There will undoubtedly be some responses to the Stanhill piece at some point, and we’ll go into some more detail at that point…. – gavin]

    Comment by Dave Reay — 25 Feb 2007 @ 6:43 AM

  99. #92

    Ferdinand, the general problem with timing / spatial convergence is that we need a good evaluation of both phenomena (dimming/brightening and anthropic aerosol emissions) and that’s hard to get. Comparisons between measurements from surface pyranometers (like GEBA and BSRN networks) and air-quality assessment would probably be the more precise for local analysis of land-station evolution (but may be too scarce for a continental / global assessment, notably the much more problematic nebulosity).

    As I mention in my previous post, Streets at al. 2006 (thereafter) fond a rather good correlation between trends in surface insolation and in SO2/black carbon emissions.

    GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L15806, doi:10.1029/2006GL026471, 2006

    Two-decadal aerosol trends as a likely explanation of the global dimming/brightening transition

    David G. Streets, Ye Wu, Mian Chin
    Abstract- Global average trends in solar radiation reaching the Earth’s surface show a transition from dimming to brightening that occurred in about 1990. We show that the inter-annual trend in solar radiation between 1980 and 2000 mirrors the trend in primary emissions of SO2 and black carbon, which together contribute about one-third of global average aerosol optical depth. Combined global emissions of these two species peaked in 1988â��1989. The two-decadal rate of decline in aerosol loading resulting from these emission changes, 0.13% yrâ��1, can be compared with the reported increase in solar radiation of 0.10% yrâ��1 in 1983â��2001. Regional patterns of aerosol and radiation changes are also qualitatively consistent. We conclude that changes in the aerosol burden due to changing patterns of anthropogenic emissions are likely contributing to the trends in surface solar radiation.


    For China precisely, the draft of another work from Streets 2006 can be read here (link > pdf). He observes a peak around 1994-1996 for carbonaceous aerosols and SO2 over East Asia:


    Anyway, I agree with you, anthropic aerosols probably don’t tell us the whole story. For example, Wong et al. 2006 find the same trend over Tropics (20 N – 20 S TOA SW upward from ERBE, compared to other sources) and they acknowledge nebulosity rather than aerosols is a better candidate for this Tropical brightening from 1980s to 1990s.
    Wong, T., B. A. Wielicki, R. B. Lee, III, G. L. Smith, K. A. Bush, and J. K. Willis, 2006: Re-examination of the Observed Decadal Variability of Earth Radiation Budget using Altitude-corrected ERBE/ERBS Nonscanner WFOV data. J. Climate, 19, 4028-4040

    Comment by Charles Muller — 25 Feb 2007 @ 7:48 AM

  100. Re #97: You say “Incidentally, inducing short-term cooling by setting off volcanoes with nuclear weapons is a bad idea, for many reasons, but is on par with the other geoengineering proposals.”

    Is it such a bad idea, though? Certainly it’s not something to do lightly: I’d consider it the terrestrial analogue of coronary bypass surgury. Far better to convince your patient to exercise & eat reasonably, and so make the risk & expense unnecessary.

    Unfortunately, we seem to be faced with a patient who isn’t willing or able to make such lifestyle changes. Even supposing the world could be convinced to take a cold-turkey cure for its addiction to fossil fuel burning, it seems reasonable to suppose that just the ongoing effects of having 6+ billion people living on the planet – no matter how gently each one treads – might push the climate to the point where feedbacks become self-sustaining.

    In such a case, I for one would really prefer to have other options available. Setting off a few nuclear explosions in unpopulated areas (perhaps in mid-ocean) certainly seems preferable to the predicted consequences of severe global warming. Not to mention that, unlike all the other geoengineering schemes I’ve read of, it could be done on short notice, and at little expense.

    Comment by James — 25 Feb 2007 @ 1:05 PM

  101. RE#98,
    There is a far better news report available on the global dimming issue than Sherwood Idso’s “CO2 science” magazine, which really represents the worst of the worst when it comes to accurate scientific information on global warming. Try (Feb 2006)

    One of the main questions is this: what data is Stanhill using? ( ) A single set of measurements from Israel means very little; neither do six isolated sites. Aerosols are highly variable in space and time, and what is needed is better data collection. Stanhill completely fails to mention any uncertainties in the data, but spends a good deal of time (the entire second page) claiming that climate science is unreliable since the IPCC ignores his work.

    From the above abc report on surface radiation measurements: “The observations we have at this point just aren’t good enough,” said Robert Charlson of the Department of Atmospheric Sciences and Department of Chemistry at the University of Washington in Seattle. “The biggest single problem we have now is a lack of adequate satellite measurements, and the platforms that could be moving us toward answers are either pending or being killed.”

    In fact, last month NASA scrapped a program that might have offered key evidence one way or the other. Initially dubbed “Goresat” by Republicans in Congress because it was first promoted by Vice President Al Gore in the late 1990s, the Deep Space Climate Observatory was designed to hover and observe an entire sunlit side of the Earth for long periods.

    The satellite, Charlson argues, might finally have offered solid data about so-called global dimming – as well as warming. The device was built and scheduled to launch in 2001. The 2001 terror attacks and then the loss of Columbia in 2003 pushed the launch date farther and farther away. Finally, NASA science chief Mary Cleave wrote scientists early this year saying that “the context of competing priorities and the state of the budget for the foreseeable future precludes continuation of the project.”

    Groups like don’t seem to want better data – they want uncertainties which they can use to question the reality of anthropogenic global warming. Paleoclimate and computer modeling studies are critically important, but the strongest evidence continues to come from real-time comprehensive data collection from the oceans and from space. The lack of funds for climate satellites and ocean sensors that would help answer these questions seems like a stalling tactic – and is a travesty.

    Comment by Ike Solem — 25 Feb 2007 @ 1:06 PM

  102. #98 Gavin response

    A point we sometimes discussed, but I still miss : why a transient increase of X W/m2 surface insolation cannot be translated in a transient decrease of X’ W/m2 of TOA albedo, and then compared to another TOA forcing (like GHGs) over the same period of time? (I suppose X’ maybe a little different from X because of diffusion of solar radiation in atmospheric layers). Another way to put it : you can observe global dimming or brightening by a TOA measurement of outgoing SW flux (lile ERBS-WFOV in Wong 2006) and then you get a value which can be included in a (transient) TOA radiative budget.

    Of course, such comparisons are transient by nature, and do not adress the question of long term influence of each forcing on climate neither equilibrium response to them. But what Dave Reay seems to question, and G. Stanhill in EOS paper, is precisely the recent changes 1960-2000 and the seemingly indifferent position of IPCC toward the significativity of global dimming / brightening for its analysis, despite the huge amounts of energy involved. (Even if on this last point, the 20 W/m2 mentioned by Stanhill is surely questionable).

    [Response: I think I’ll do a full post on this since it comes up a lot. Watch this space… – gavin]

    Comment by Charles Muller — 25 Feb 2007 @ 2:53 PM

  103. #101

    To be fair, G. Stanhill mentions “six isolated sites”, but also refers to a bibliography of 70 papers or so on global dimming / brightening :

    Nobody question the fact that there are uncertainties in the measurement. For example, that’s why Martin Wild chose to give a qualitative estimate in his 2007 GRL paper (surface insolation still inferior in 2000 than in 1960), rather than a more precise quantitative estimate (as I ask him for the reason, he explained me by mail that he was currently working to such a regional / global estimate from the 1,600 sites of GEBA network).

    Nevertheless, the important point is that a lot of independent measurements converge toward the same conclusion (that is surface insolation from pyranometers, TOA SW flux, ISCCP data on nebulosity, Earthshine reflectance on the moon, vegetal productivity index as a proxy for solar incoming radiation, etc.) and that most regional studies seem to confirm the global trend. So, I think we cannot objectively summarize the case in suggesting Stanhill is just furious of the IPCC indifference for his personal work or CO2 Science is manipulating the opinion.

    Comment by Charles Muller — 25 Feb 2007 @ 3:53 PM

  104. RE: 75, 83 and 94
    Sincere thanks for the responses,

    I have a follow up question. Given that CO2 is the predominant non-H2O greenhouse gas, is it possible to provide an approximate answer to the question; what would surface temperature be if only CO2 were removed? Ignore ice-albedo effects but allow water vapor to equilibrate to the new temperature. I would think the temperature drop from current (285 K) would be nearly as large (approaching 30 degrees K).

    I would also imagine the ice-albedo effect would be similar (approaching 25 degree K).

    Just to remind, I am asking these questions because I think the arguments currently used to explain the role of CO2 are unpersuasive. After all if water vapor is the dominant greenhouse gas why do scientists ignore it while focusing on CO2 particularly given the uncertain role of clouds. This is a rhetorical question, I understand the physics, but from the standpoint of an explanation for non-scientists what is needed is a simple dramatic uncontested argument proving CO2 plays a dominant role as a greenhouse gas.

    [Response: See our previous posts for the relative roles of water and CO2: . Without CO2, the majority of the current greenhouse effect would disappear, but it’s difficult to be precise since you very quickly get into regimes where the physics is not likely to be well captured in GCMs. -gavin ]

    [Response: I don’t entirely agree with Gavin that GCM physics are not up to the cold no-CO2 case. I do cold climates all the time in my Neoproterozoic Snowball work, and the major uncertainties are mostly where they always are — in the cloud parameterization. The answer to your question rests on whether you want to include ice-albedo feedback or not, and if you do want to include it, whether the ocean dynamics keeps the Earth from freezing over completely when you take out the CO2. I haven’t gotten around to doing a modern-day case, but in the Neoproterozoic, when the Sun is slightly fainter, you can in fact get the Earth to freeze over (without ocean dynamics) by dropping CO2 to 100ppm; you don’t even need to take it all out. A rough estimate allowing for the brighter Modern sun suggests very strongly the Earth would freeze over completely if you took out all the CO2, at least in the absence of ocean dynamics. When the Earth freezes over completely, the global mean temperature drops to under 230K, and there is essentially no water vapor greenhouse left. The cloud greeenhouse effect remains, however. With ocean dynamics, it’s a little dicey to say whether the Earth would freeze over under modern conditions, if you took out all the CO2, and that’s where the main uncertainty lies in answering your question, –raypierre]

    Comment by Daniel Morris — 25 Feb 2007 @ 4:10 PM

  105. RE#103,
    Well, why doesn’t Stanhill discuss the uncertainties in the data? This is such a typical thing – to see very sketchy data widely promoted by groups such as AEI, CO2science, etc. – but only if it indicates the result they are looking after. In contrast, just about every article that appears on realclimate contains an objective discussion of the uncertainties present, whether it be aerosols or solar forcing or volcanic forcing or climate models.

    Surface radiation data can be influenced by clouds, local production of aerosols – a whole list of factors. Climate contrarians latch onto such uncertainties – if there is an uncertainty about clouds, for example, you’ll hear the argument that some clouds will reflect sunlight and so cool the planet, and you’ll also hear that some clouds warm the surface, and so less cloudiness will cool the climate… it’s a result (negative feedbacks will cool the climate) in search of supporting data, an approach which generally produces low-quality science.

    When has a group such as AEI, CEI or the George C. Marshall Institute ever called for more funding for real-time data collection to help resolve the uncertainties? Never.

    Comment by Ike Solem — 25 Feb 2007 @ 4:27 PM

  106. I read the article referenced in comment 104. With the magnitude of uncertainties involved in water vapor and other atmospheric absorbers I find it impossible to belive that the error function associated with CO2 can be calculated to a resolution of +/- 0.005 w/m2 as the opening article indicates.

    As a physicist and engineer (degree in engineering physics) I would like to find out the basis for calculations with this small level of uncertainty. Could you point me to the data and equations that allow for this level of accuracy? This is especially interesting in that the data from ACRIM3 and other solar monitors indicate an increase in solar output at a rate of change of 0.57 w/m2 since 1978.

    This is a sincere request as I really do want to follow the science where it leads and the experimentalist part of my brain raises an alarm where results of this type are reported.

    [Response: Where do you read that? radiative forcing from CO2 (and other GHGs) is known to about 10% (i.e. +/-0.17 W/m2 on the main estimate of 1.7 W/m2). Nothing in this is known to the level you suggest and I don’t see how you’d understand otherwise. -gavin]

    Comment by Dennis Wingo — 25 Feb 2007 @ 5:31 PM

  107. Just a little heads up on Dennis Wingo.

    He’s been cooking numbers in this manner for years.

    [Response: And talk about cooking the books! I defy anybody to look at the ACRIM solar irradiance data in and find anything like support for .57 W/m**2 trend in the data. Moreover, even if the trend were there, to turn that into radiative forcing, you have to multiply by (1-albedo) and divide by 4 (to account for averaging over the Earth’s surface). That knocks you down to under a tenth of a W/m**2 of radiative forcing. But, averaging out solar cycles, the data does not seem to support a trend with any reliablility. Note further that ACRIM consists of three satellites. There’s a data gap between the first and second, and during the overlap between the second and third the two satellites do not match. This is hardly auspicious for Solar trend-spotters. –raypierre]

    Comment by Thomas Lee Elifritz — 25 Feb 2007 @ 6:55 PM

  108. #105

    Ike, Stanhill has published a dozen papers on the global dimming question, from his first paper on trend in Israel (1992) to the most recent concerning USA 20th Century (2005). I guess in each one he had to quantifiy the uncertainty of the trends he reports. In EOS 2007, he published in the Forum section, with a quite provocative style, and clearly want to initiate a debate over this question. This debate will be useful.

    Resolve the uncertainties is certainly an important matter for climate sciences. We know that such uncertainies are unfortunately elsewhere, even in the satellite era (no consensus on the rate of tropospheric warming, the value of TSI, the reality of nebulosity trends, etc.) and I don’t speak of more ancient measurements whose scarcity / imprecision lead to some problematic homogeneizations or interpolations. (Concerning our subject, +/- 5 W/m2 of margin error for mensual means in GEBA, +/- 2W/m2 for annual means… and no station over oceans, 70% of the Earth surface). There’s a lot of work and we need to continuously improve the monitoring (so, on a more political point of view you’ve perhaps in mind, we need more rather than less climate science and climate scientists!)

    I would formulate the basic problem adressed by Stanhill tribune in that way: is TOA forcing the better way to attribute (pluri-)decadal changes in surface temperature if these changes are modulated by other radiative evolutions (between tropopause and surface), their direct heating as well as their indirect consequences on circulation ?

    I think the Romanou et al. 2007 paper Gavin has posted will help to clarify the question, and to understand the relative impact of these factors on model simulations. But I’ve still to read it!

    Comment by Charles Muller — 25 Feb 2007 @ 8:06 PM

  109. Ray:
    Re: the snowball Earth, does the length of the day (23.5 hours vs 22 hours) make any difference in how little CO2 you need to freeze the Earth? Would it be worth putting up a post on neoproterozoic climate?

    Comment by C. W. Magee — 25 Feb 2007 @ 10:39 PM

  110. There is a file on the NOAA ftp site where the solar data is kept that is a composite of data from ACRIM1, Nimbus 7/ERB, ACRIM2 and ACRIM3. The data set was graphed by RC Wilson, and the graph file is earth_obs_fig9 05/21/2003.

    The Total Solar Irradiance (TSI) trendline between solar minimia since 1980 is 0.037%. per decade. That translates into a Total Solar Irradiance increase of about 0.50 watts/m2/decade.

    I would like to know how exactly this plays into your calculations and would like to see the equations of state that gain you only 0.15w/m2.

    [Response: There’s no equation of state involved. There’s just energy balance. You obviously don’t understand that, so you should go read an elementary textbook before you sound off. Before people go believing in any such mythical trendline, they should look at the difficulties in splicing together multiple satellites. Actually, your honesty impresses me just a little. I would have expected you to make a trendline by connecting the minimum of one solar cycle with the maximum of another. That’s about the level of logic of most solar-boosters, so you’re doing a bit better than most. –raypierre]

    Comment by Dennis Wingo — 25 Feb 2007 @ 11:29 PM

  111. RE#108
    The question of how to get a good value for top-of-atmosphere (TOA) forcing was the subject of another RC commentary. (Aerosol-tour-de-forcing Feb 2006)

    Relevant quote:
    “The new generation of satellite instruments is at the heart of recent attempts to reduce the large uncertainty of direct radiative forcing by aerosols. Each of these studies provides an estimate of the most likely value, along with a range of uncertainty. Bellouin et al. (2005) in Nature arrive at TOA forcing of -0.8 ± 0.1 W/m2. While near the center of the range published by the IPCC, this estimate is noteworthy for its comparatively small uncertainty. Yet on the same day, Chung et al. (2005) published an article in the JGR, estimating based upon similarly extensive calculations that the forcing by aerosols at TOA is -0.35 ± 0.25 W/m2. A few months earlier, Yu et al. (2005) had estimated a more conciliatory value of -0.5 ± 0.33 W/m2. The wide range of estimates give some indication the difficulty of the problem.

    Forcing estimates differ not only at TOA but also at the surface: Bellouin et al. predict that aerosols reduce the net radiation incident upon the surface by 1.9 ± 0.2 W/m2 compared to 3.4 ± 0.1 W/m2 for Chung et al. (2005). That is, Chung et al. estimate much greater atmospheric absorption. Because radiation into the surface is mainly balanced by evaporation, except within extremely arid regions, the discrepancy has implications for the supply of moisture to the atmosphere. Chung et al. estimate a much larger reduction in global rainfall by aerosols.”

    Now, the Stanhill article claims that there is a -20 W/m2 reduction in surface solar radiation, obviously far too large to be accounted for by aerosol forcing. However, there are only six sites in the paper – can you imagine how contrarians would howl if scientists tried to claim there was a global warming trend based on temperature records from six isolated sites? Then Stanhill goes on to insinuate that climate science is a ‘trans-science’ that poses questions it is incapable of answering! Sour grapes, anyone?

    What is needed is the Deep Space Climate Observatory, which was designed to hover over the sunlit side of the Earth for long periods, at Lagrange 1 between the sun and the Earth. See for a description of how this project was killed. Incidentally, none of the sites like CO2science or AEI even mention the DSCO.

    What’s even more remarkable is how Roger Pielke Jr. defends the killing of the satellite (2006).

    This is the standard approach of the climate contrarians, and just shows how intellectually dishonest their stance really is.

    Comment by Ike Solem — 26 Feb 2007 @ 12:13 AM

  112. TSI @ 1 AU (w/m2)
    ACRIM Composite TSI Time Series (Daily Means) *
    TSI trend (solar cycles 21 – 22 minima): 0.037 %/decade
    TSI trend (solar cycles 22 – 23 minima): ~0.025 %/decade
    TSI trend (solar cycles 21 – 23 minima): 0.006 %/decade

    Comment by Hank Roberts — 26 Feb 2007 @ 12:15 AM

  113. #110 Dennis, Earth is a sphere (4pi*r2) not a disk (pi*r2) and albedo (a) partly reflects incoming radiation. So the effect of any TSI variation X in a TOA budget is X*(1-a)/4 (an usual approximation is X*0,18). ACRIM (thart is Willson 2003) do find a slight trend in TSI/TOA forcing (0,05W/m2/dec TOA), but not PMOD (Frohlich 2005) nor IRMB.

    Comment by Charles Muller — 26 Feb 2007 @ 7:10 AM

  114. [[what these statements assume is that manmade CO2 emissions are causing AGW. ]]

    Explain how one can increase the amount of CO2 in the atmosphere and not increase the temperature of the ground. Even if you’re right and there are substantial negative forcings, how could they increase just so as to keep pace with CO2?

    Comment by Barton Paul Levenson — 26 Feb 2007 @ 8:28 AM

  115. Re #87 Thanks Blair, that’s very useful. I’m certainly among those who did not realise the amount of time it would take for a reduction in fossil fuel use to produce a net reduction in the rate of warming, due to aerosol effects! Two thoughts:
    1) This emphasises the need to work on sources of CH4, N20 and other non-CO2 GHGs; on sources of CO2 that don’t also produce cooling aerosols; and on CO2 sinks, if indeed there are any we can amplify without producing worse problems.
    2) Maybe (just maybe) we will need to think about other ways to reduce warming, like putting aerosols in the stratosphere, despite all the drawbacks, if this is necessary to avoid drastic changes like disruption of the monsoons, or positive feedbacks kicking in.

    Comment by Nick Gotts — 26 Feb 2007 @ 8:49 AM

  116. [[If (anthro) aerosols have a huge influence, then the sensitivity for GHGs is high, if aerosols have a low influence, then GHGs have a low influence too. ]]

    Non sequitur. The sensitivity of greenhouse gases doesn’t depend on aerosol effects unless the aerosol effects are somehow linked to the greenhouse gases as a feedback. As far as I know, they aren’t.

    Comment by Barton Paul Levenson — 26 Feb 2007 @ 9:39 AM

  117. #116 I think the assertion you quote is not a physical reasoning (interaction between GHGs and aerosols), rather statistical (attribution warming/forcing).

    You’ve the 0,75 K warming 1850-2005 and a net anthropogenic forcing in the range 0,6-2,4 W/m2 (SPM 2007), aerosols being the most uncertain value.

    – If aerosol effect is high (anthropogenic net forcing tends toward the lower value 0,6 W/m2), you’ve a high sensitivity to human forcing (0,6 W/m2 > 0,75 K).

    – If aerosol effect is low (anthropogenic net forcing tends toward the higher value 2,4 W/m2), you’ve a low sensitivity to human forcing (2,4 W/m2 > 0,75 K).

    Of course, it’s a rough estimate (transient climate response is not the same matter that equilibrium sensitivity, for example).

    Comment by Charles Muller — 26 Feb 2007 @ 10:03 AM

  118. 110, 112
    Sorry for the garbles; those are interval dashes and a minus symbol in that data.
    Our Mr. Wingo here perhaps is not the well known ‘rocket scientist’ named Dennis Wingo?;
    he picked only the one largest cherry and based his claim on that as a trend:

    TSI @ 1 AU (w/m2)
    ACRIM Composite TSI Time Series (Daily Means) *
    TSI trend (solar cycles 21 – 22 minima): 0.037 %/decade
    TSI trend (solar cycles 22 – 23 minima): -0.025 %/decade
    TSI trend (solar cycles 21 -23 minima): 0.006 %/decade

    Comment by Hank Roberts — 26 Feb 2007 @ 10:12 AM

  119. Hank

    Then you would agree that the data from ACRIM is good data? It will be interesting to see what happens in cycle 24 when at least half of the solar heliophysics community is forecasting a decrease in activity relative to former cycles and the other half expecting a big one.

    Charles, yep, know that, nor is it a flat plate as some still suspect. :)

    Ray, I don’t know where you begin your science but climate is a state machine and all of your simulations have to begin with a beginning state for all of the variables or you would not be able to do your simulation, hence the equations of state that govern the state of the system at any one instance. Energy balance is just one of the variables in a state machine process. This is how I run simulations for many types of systems. From everything that I have seen on climate systems you put in all of the variables and then simulate the response, achieving a system where at any point in time, you can forecast the state of the system. Theoretically that system can be run backward and forward to verify fidelity against the know prior states of the system. That is how simulation works.

    Oh, also, yes I do spacecraft design as my day job and my interest in climate systems actually derives from observing the influence of the Sun on the design of solar power systems on spacecraft and the fact that I worked at the Center for Space Plasma and Aeronomic Research (CSPAR) at the University of Alabama in Huntsville under Dr. S.T. Wu.

    I did see a book referenced here that I am going to buy, the hard science of CO2. I have not found adquate reseources on the internet that delves into the basic physics involved in CO2 as an extinction coeifficient and its role in trapping long wave infrared radiation. I have an admitted bias to look at solar forces as it should be intuitively obvious to the casual observer that the Sun is the first order influence on climate. My experience tells me that water vapor is number II and at best CO2 is number III. I am more than willing to be convinced of the science but I have yet to see the basic physics of the whole process laid out in the gross detail that it needs to be.

    Comment by Dennis Wingo — 26 Feb 2007 @ 11:46 AM

  120. > agree …good data?
    I know nothing about that data. I know only that you picked one number and claimed a trend; the other numbers belie that trend.

    Climate Change: Discovery of Global Warming
    … supplements his much shorter book, which tells the history of climate change research as a single connected narrative …
    American Institute of Physics (AIP)

    Comment by Hank Roberts — 26 Feb 2007 @ 1:04 PM

  121. [[- If aerosol effect is high (anthropogenic net forcing tends toward the lower value 0,6 W/m2), you’ve a high sensitivity to human forcing (0,6 W/m2 > 0,75 K).
    – If aerosol effect is low (anthropogenic net forcing tends toward the higher value 2,4 W/m2), you’ve a low sensitivity to human forcing (2,4 W/m2 > 0,75 K).
    Of course, it’s a rough estimate (transient climate response is not the same matter that equilibrium sensitivity, for example). ]]

    I don’t care about how rough an estimate it is. The methodology is fundamentally wrong.

    I don’t think you understand what I said in my earlier post. You’re assuming these things are all tied together somehow. They aren’t. The radiative forcing from CO2 will be the same whatever the aerosol forcing is.

    [Response: We discussed this in some detail previously: – it’s a pretty prevalent confusion. -gavin]

    Comment by Barton Paul Levenson — 26 Feb 2007 @ 2:39 PM

  122. [[Ray, I don’t know where you begin your science but climate is a state machine and all of your simulations have to begin with a beginning state for all of the variables or you would not be able to do your simulation, hence the equations of state that govern the state of the system at any one instance. Energy balance is just one of the variables in a state machine process. This is how I run simulations for many types of systems.]]

    Let’s see, you design spacecraft. Ray has been working with climate models for at least a decade (cf the seminal paper Forget and Pierrehumbert 1997 which established wide habitable zones of stars once and for all). Who probably knows how to model climate better? The scientist who actually does it for a living, or the engineer?

    Comment by Barton Paul Levenson — 26 Feb 2007 @ 2:49 PM

  123. RE#119, Dennis if you have a background in solar PV design for spacecraft and can’t find the many, many references on the internet that describe radiation models in the atmosphere then you must not be looking. An introduction to the topic can be found at There are endless technical papers available that go on from there. If you “have yet to see the basic physics of the whole process laid out in the gross detail that it needs to be” then you simply aren’t looking. Go to Google or to Google Scholar and type in: “CO2 radiative convective models” – about half a million hits from Google, about 14,500 from Google Scholar.

    Comment by Ike Solem — 26 Feb 2007 @ 2:53 PM

  124. Barton

    Then I guess that his comment was of the snarky variety. I always respond as if the poster is sincere until proven otherwise.

    Comment by Dennis Wingo — 26 Feb 2007 @ 6:38 PM

  125. #121 and Gavin link

    I don’t think CO2 climate sensitivity itself depends on aerosol forcing : it depends on climate feedbacks to an increase of CO2 (ice, carbon cycle, water vapour, lapse rate, nebulosity, etc.). But I think the empirical estimate of climate sensitivity from current modern warming do depends on our estimate of aerosol forcing (as well as the empirical estimate of climate sensitivity from LGM-Holocene transition depends of our good evaluation of other forcings: mainly dust, vegetation and ice albedo).

    Unless I don’t understand the article we’re commenting, that is exactly what I read here :

    “In addition, our deficient understanding of aerosol forcing also hinders our ability to use the modern temperature record to constrain the “climate sensitivity” – the operative parameter in determining exactly how much warming will result from a given increase in CO2 concentration. The determination of climate sensitivity has been discussed in this forum previously here. The sensitivity parameter can be derived by examining historical records of the correlation of CO2 concentration and temperature taking into account other contemporary changes. Aerosols contribute significantly to the uncertainty in climate sensitivity because we cannot model their historical impact on the temperature record with sufficient accuracy, though additional constraints on climate sensitivity such as the last ice age do exist. A better understanding of aerosols then may well facilitate more accurate predictions of future climate responses to changing CO2″

    So when you say : “The radiative forcing from CO2 will be the same whatever the aerosol forcing is”, I’m OK with you. But my point is : our evaluation of transient climate response to GHGs change (and by extension of climate sensitivity) would be better if we estimate aerosol forcing as precisely as GHGs. And it would be quite different if this forcing is -0,4 W/m2 or -2,7 W/m2 (the two extremes of the current range).

    Comment by Charles Muller — 26 Feb 2007 @ 7:20 PM

  126. Re #115: Nick, please be aware that my calculation was intended to get a rough idea of the time it takes before closing a fossil fuel emission source actually leads to cooling. The results should not be taken too literally. Rather than using global figures (which include many things), a better method would be to calculate the forcing of CO2 and aerosols from a single (for example) coal plant.

    Comment by Blair Dowden — 26 Feb 2007 @ 7:21 PM

  127. Barton

    Careful, your implied disparagement of an engineer (my degree is in physics and I have an engineering background) is not nice. I can calculate as well as he can. I also have been designing computers for the past 25 years and understand their limitations and advantages, probably considerably better than most who don’t do that activity.

    Ike, thanks for the very good link. I know some of the people involved, including Dr. John Christy, from the Center for Global Hydrology. Here is what he had to say about Hanson’s modeling work.

    An examination of first order climate forcings, as reported in NRC (2005) shows that important ones are neglected in the Hansen et al. study (e.g., the biogeochemical effect of increased CO2 ; the thermodynamic indirect aerosol effect). To use a value of -0.77 Watts per meter squared for the selected climate forcing for the indirect aerosol effect in the Hansen et al. paper is not justified at this precision and seems to be used to fit the model to the observations. By fitting the models in this manner, the role of other first order climate forcings could be incorrectly missed.

    And this:

    Therefore, while we agree on the value of using ocean heat storage changes to assess the Earth’s radiative imbalance, the Hansen et al. study omits addressing important scientific issues which are essential in order to permit more confidence in the accuracy of the model simulations of the Earth’s climate system.


    One would think that someone who works with energy balance simulations would have been aware of these objections.


    The bottom line is that I really appreciate the links to the models, I will delve into them as simulation is one of my forte’s. It is also quite clear that my initial instinct was correct that it is inappropriate, at this time, to ascribe three significant digits to any estimation of GW forcing. In the astrophysics that I have done, I would have gotten a bad grade for not understanding the error limits of my data.

    Another question that I have not seen addressed anywhere.

    I have downloaded and run the CO2 concentration data from Mauna Loa. In the late 50’s the delta between winter and summer CO2 was approximately 2 parts per million. In recent years this has increased to 4 parts per million delta. I have carried out some tree ring studies in the high Sierra Nevada (would be more than happy to post the pictures), that indicate increased productivity in trees which would seem to be confirmed by the delta increase in CO2 concentrations from Mauna Loa. The increase would seem to indicate that the productivity of plant growth in the Northern hemisphere has doubled in the last 50 years and yet I see no reference to this anywhere. Have there been any studies of the increase in amplitude of the seasonal variation of CO2 in the last 50 years?

    Climate is a facinating subject.

    [Response: Context. This is an excerpt from a rejected comment from Pielke and Christy on a Science paper I was co-author on, and for which our reply is also available: along with the comments from the reviewers of the exchange: – gavin]

    Comment by Dennis Wingo — 26 Feb 2007 @ 7:28 PM

  128. Thanks for that.

    This comment by reviewer 2 does go to the heart of my objection:

    None of the participants in this pathetic exchange seem to have the slightest clue about the large
    decadal noise that exists in the oceans and some ocean models. If they did they would not make the
    comments and calculations they do. A decadal of data and analysis leave no room, after natural variability
    in the ocean is considered, to make statements about global warming issues. Further, the sparse nature of
    the ocean observations makes statements about “global ocean warming” highly unrelaibale. The
    interpolations done by Levitus have been shown to lead to potentially misleading conclusions. The use of
    the altimeter by Willis et al looks good but is likely to miss any baroclinic signals in the upper ocean that
    might impact the estimates of heat content in the upper 750m.


    I do appreciate the exchange and emphasize that I am still on the learning curve for this whole subject. With the amount of variability involved I am not convinced at this point to exclude solar influences. I do know that there is a disconnect between the disciplines of solar physics and atmospheric physics and the links provided do tend to reinforce this perception.

    [Response: I’m glad you recognize you are still on the learning curve. I take some umbrage with people who pontificate about climate without having even attained an understanding of the subject at a decent high-school level (like not understanding why you divide total solar irradiance by 4 and multiply by coalbedo, and nattering on about “equations of state.” ) Then, when such people go on to declare that they, in their wisdom, have a feeling that it’s really The Sun, because The Sun is obviously kinda important to keeping the Earth warm, and complain that they’ve never seen the equations of radiative transfer laid out (when they can be found perfectly clearly laid out in Goody and Yung or Liou’s radiation books,or Houghton’s Physics of Climate book), well, of course it rubs me the wrong way. It gets compounded when people decide to look at a trend in trough-to-trough when an average over the solar cycle is more relevant, and then ignore the considerable errors in attempting to splice multiple satellites together, when there are gaps in the record. We see a lot of this — people who have learned to simulate appearing calm and learned when really they are ridiculous. It’s hard for the uninitiated reader to know what is ridiculous and what is learned. I’m sorry if it may hurt, and it gives me no pleasure, but it’s part of my job to point out who is ridiculous. –raypierre]

    Comment by Dennis Wingo — 26 Feb 2007 @ 8:29 PM

  129. Hank

    The ACRIM3 data that gives the 0.06 w/m2 decade has only been gathered in the last nine months as we have reached the bottom of cycle 23. One would expect a lag for climate effects to occur. I am really waiting to see who’s predictions for cycle 24 come true. It is still a crap shoot at this time although the magnetic data points to a quieter peak this cycle.

    Comment by Dennis Wingo — 26 Feb 2007 @ 9:32 PM

  130. Ray

    There is a tendency on both sides of this discusssion to diminish the importance of the other’s data sets. As someone with much more knowledge on the solar side and on the side of the design of spacecraft instruments I can see the weakness of your response on that side as you have pointed out things where I am still climibing the learning curve.

    I can point out that there is still little understanding of the impact of the total radiative output of the sun (Which is different than the Total Solar Irradiance) and the influence of the Sun’s magnetic fields in transferring energy to the Earth through its magnetic field. Large magnetic storms transfer thousands of terawatts of power into the earth’s magnetic field and yet this is not taken into account any any model that I have ever read about. This goes to the core of the dichtomy related to why high sunspot counts bring global heating.

    I ran a simple model a few years ago that was based on the Earth/Sun system as an electronic circuit (an RLC circuit to be exact) to look at the terms that govern disspation (the resistance part) of solar magnetic energy into the Earth’s surface. This has only recently been admitted by any of the communities with the discovery of the “vertical” lightning that transfers energy between the ionosphere and the mid and low lattitude lower atmosphere. When you model the Earth as a capacitor (the surface being one plate, and the ionosphere the other and the atmosphere being the dielectric) interesting things occur among which is the theoretical foundation for the energy transfer of the sprites and other vertical lightning phenomenon.

    There are also the Shauman (spelling of the name not right) resonances between the ionosphere and the earth (4, 6, 12, and 16 hz) that transfer energy into the Earth system and provide input to your total energy balance equations and yet these inputs do not exist in any model that I have seen.

    The uncertainties are very high for these inputs and I certainly would advocate more orbiting missions as well as terrestrial monitoring to better define these energy inputs.

    The bottom line is that it does not take a rocket scientist to see that the fidelity of the models is not high enough to support the magnitude of claims that are made about them today and their ability to predict or even understand the totality of climate. A little more science and a little less hubris does seem to be in order and a slightly smaller bias to attack those who disagree with you.

    [Response: I agree it doesn’t take a rocket scientist to understand such things, but I am chagrined that a rocket scientist, such as yourself, shows so little regard for the need for quantification. Some said that Crichton had no qualifications to comment on climate science because his degree was in medicine. I never agreed with that. I always felt that the basics of the energy balance determining the climate system are the sort of things that any well educated scientifically literate non-professional could understand. It is distressing when people don’t take the minimal effort needed to understand. None of the things you say above make the least bit of sense. You turn the “ionospheric resonance” stuff into an energy forcing and I’ll start to pay some attention to what you have to say. The energy density directly attributable to the solar magnetic field is negligible at the Earth’s orbit. That’s why Svensmark and his crowd are so eager to find a cosmic-ray amplifier (which in fact doesn’t work, because there is no observed GCR trend, and if the effect on clouds were large we’d see it in the Laschamp anomaly). You are the one who is displaying hubris, and you are the one who could use more science. All you’ve given us is the equivalent of a Potemkin village. Lots of high-sounding words, but nothing behind it. –raypierre]

    Comment by Dennis Wingo — 26 Feb 2007 @ 11:21 PM

  131. [Note to the Moderators]

    I really don’t have anything to add here, having gone through this same discussion countless times before with Mr. Wingo, other than to say it is a great pleasure for me personally, to have Dennis Wingo post his craft here.

    Pseudoscience is clearly advancing by leaps and bounds in the faith based rocket design world.

    Comment by Thomas Lee Elifritz — 27 Feb 2007 @ 12:19 AM

  132. Yep, a bit of Google time reveals patterns, doesn’t it?

    Comment by Hank Roberts — 27 Feb 2007 @ 12:48 AM

  133. Re response to #130: You turn the “ionospheric resonance” stuff into an energy forcing and I’ll start to pay some attention to what you have to say.

    Although I agree that without any empirical measurements that backup the possibility of some of that huge amount of magnetic energy getting indirectly transferred as an energy forcing back to the Earth, it should be ignored in the models. Conversely, however, distinctions should be made about conclusions derived from empirical data (eg. Current global warming is almost certainly anthropogenic) and conclusions derived from models ( eg. Radiative forcing component uncertainties). This is because that which is derived from empirical data is based on ACTUAL observations (you know science can only know things through experiment and repeatable results). The uncertainties which are derived from models only take into account the known unknowns. Of course, it is the unknown unknowns which is what future scientists will discover and make the current generation look stupid. However, there is enough uncertainty built into the “climate sensitivity” aspect that it is unlikely that you yourself will look stupid. However, it may be wise to not take any bets where calculations based on empirical data are currently impossible due to correlated human activity.

    Comment by Marco Parigi — 27 Feb 2007 @ 1:59 AM

  134. [[Careful, your implied disparagement of an engineer (my degree is in physics]]

    So is mine.

    [[ and I have an engineering background) is not nice. I can calculate as well as he can. I also have been designing computers for the past 25 years and understand their limitations and advantages, probably considerably better than most who don’t do that activity.]]

    The fact remains that you are lecturing someone who has worked with climate models for decades when you have never written such a model. I see this a lot in engineers — they not only think they’re scientists; they think they’re qualified to say where the scientific consensus is wrong, even if they themselves have never published a single paper in a peer-reviewed journal. It didn’t surprise me to find out that a lot of creationists and believers in Velikovsky’s astronomy are engineers. They think if you can manipulate equations, that makes you a scientist.

    Comment by Barton Paul Levenson — 27 Feb 2007 @ 8:12 AM

  135. [[I can point out that there is still little understanding of the impact of the total radiative output of the sun (Which is different than the Total Solar Irradiance)]]

    Huh? What? Come again?

    [[ and the influence of the Sun’s magnetic fields in transferring energy to the Earth through its magnetic field. Large magnetic storms transfer thousands of terawatts of power into the earth’s magnetic field and yet this is not taken into account any any model that I have ever read about. This goes to the core of the dichtomy related to why high sunspot counts bring global heating. ]]

    Probably it isn’t taken into account because the planet’s energy balance balances well without it, which implies that that source, if present at all, must be negligible. Can you give a quantitative estimate for how much this source adds to the energy input into the Earth’s climate system? The Solar input is, as noted earlier, about 240 W/m**2. How much comes from the energy that gets transferred into the Earth’s magnetic field?

    Comment by Barton Paul Levenson — 27 Feb 2007 @ 8:19 AM

  136. (OT)

    I’m always surprised by the “allergic” reactions to the words “sun” ou “galactic cosmic rays”. Probably it’s due to the misuses / misunderstandings surrounding these topics and the too highly politicized / personalized conflicts they’ve generated.

    Anyway, as a layman reader of IPCC statements, I notice we have a high LOSU of GHGs forcing, a low LOSU of solar forcing (among many others). So, it’s clear science has to progress on what it still doesn’t correctly understand. Gray et al. have listed major points to be gone further in their 2005 Hadley Centre technical note (#62, downloadable on Hadley website). Much job for coming years.

    I add a personal impression: one of the reason I became skeptic (even if I acknowledge and regret many exaggerations / imprecisions in usual skeptic assertions) is that the not-very-funny game of excommunications is more often played against those among scientists who suggest our current understanding of climate change doesn’t tell the whole story and is not so robust it’s usually claimed. It leaves me with the unpleasant feeling of a “mainstream” science trying to silent its “minorities” in order to preserve the so-called “consensus” essential for policymakers and public opinions. No far from what Stanhill said in EOS. Maybe climate science would be more productive in its (normal and fruitful) disagreements without IPCC, after all…

    [Response: The reaction you see is not against the sun or GCR (remember that a large number of us have authored papers on solar changes and possible responses), but against the faulty logic and spin that most often accompanies it. This relentless boosterism by some people involved in that game has tarnished the whole field and make the rest of the community very wary about any new claims. This has nothing to do with IPCC – and frankly nothing to do with Stanhill either (surface solar radiation changes have zero to do with solar activity).

    What you percieve as squashing of dissent is nothing of the sort. There are plenty of odd minority ideas in climate science that are tolerated and even encouraged (hey, you never know) – but there seems to have been a coalescence of serial exaggerators and agenda-driven science around solar studies that many people find tiresome (but sometimes laughable). There are only so many times you can say – ‘but there isn’t a trend’ before you wonder why it’s not being heard. IPCC is a target because it makes clear what the community thinks, bringing the issue a little more prominence. But IPCC or no IPCC, logical fallacies are still seen through by almost all working scientists. After all, they are all professional sceptics (in the true sense of the word). – gavin]

    Comment by Charles Muller — 27 Feb 2007 @ 9:48 AM

  137. Barton

    All I said that it was an interesting subject, worthy of study. I would agree that on the scale of 240 w/m2 it is insignificant except in transitory events such as large solar flares (in polar regions). However, that being said, one of the key pillars of CO2 research is that as concentrations increase the altitude of radiative reflections increases. What is the chemical and physical impact of Sprites and other vertical lightning phenomenon on these energy equations. The BATSE Instrument’s recording of extensive gamma rays from this source indicates very energetic processes at work in what scientifically has always been called the ignorosphere due to the difficulties involved in direct measurements. These energetic events, principally above thunderstorms in mid and low lattitudes, will effect that balance. Again, I am just looking at it from a research perspective for study, not making any definitive claims.

    Also, just going from basic principles of the study of error, there is no basis of using three significant digits in calculating GW potentials from ANY model.

    That is the only true criticism that I have and it is backed up by many studies.

    Until science is willing to face criticism forthrightly, you are going to continue to be less successful than you could be in putting forth your points.

    [Response: Unless commenters learn to read they will have difficulty in getting their points across. What part of ‘CO2 forcing is known to about 10%’ do you not get? Claiming that ‘scientists’ state unjustified certainty when they clearly haven’t and then criticising a non-existent claim, is sophmoric at best and tedious in any case. Please try to do better. -gavin]

    Comment by Dennis Wingo — 27 Feb 2007 @ 9:54 AM

  138. I often feel when talking to physicists about climate science that they like simple and cosmic answers: it’s gotto be the sun. Well, it looks like it’s way more complicated than that. But not all physicists! And not all engineers! I am a geological engineer by training myself. But I think a lot of the argument happening here is we are refusing to read what each other has published. Science is based on organized skepticism but it shouln’t be adversarial. That’s for lawyers and others who are trying to manipulate a certain outcome. It distracts from the issues when we start becoming argumentative without basis and well, aggressive in our language.

    Comment by teacher ocean — 27 Feb 2007 @ 10:21 AM

  139. Science is based on organized skepticism

    Actually, no, science is based upon evidence.

    Even skepticism must be based upon evidence.

    Comment by Thomas Lee Elifritz — 27 Feb 2007 @ 11:56 AM

  140. See, a lawyer would say justice is based on evidence and then manipulate that same evidence to push his point, not necessarily the truth. Of course science is based on evidence, but without the skepticism, the interpretation of that evidence can be misleading or simply wrong. It’s ok to be wrong in science, as long as we are willing to accept we are wrong and move on rather than mask or force the wrong idea onto others.

    Comment by teacher ocean — 27 Feb 2007 @ 12:30 PM

  141. This is the sort of claim that merits a good cite:

    > Large magnetic storms transfer thousands of terawatts of
    > power into the earth’s magnetic field and yet this is not
    > taken into account any any model …

    Later qualified:

    > All I said that it was an interesting subject,
    > worthy of study. … I am just looking at it from
    > a research perspective for study, not making any
    > definitive claims.

    Which “it” is interesting? Is “it” a fact, or a supposition?

    Clarity helps a lot for those like me who are not climate scientists, trying to understand statements made. Cites count for a lot; none of us wants to waste time checking assertions made without sources — that’s homework help, and gets old fast.

    Er, we digress (wry grin). This clearly belongs in another topic — if at all; even the claimed magnitude of the effect is rather small in comparison:

    > The typical hurricane delivers an average power output of
    > about 50-200 terawatts during its lifetime…

    For the record, this isn’t only wacko speculation, it’s also an area of research:
    Scholar — Recent articles … about 222 found searching:
    geomagnetic dynamo external influence

    Comment by Hank Roberts — 27 Feb 2007 @ 1:27 PM

  142. Re #136 (comment):


    (surface solar radiation changes have zero to do with solar activity).

    Not completely true, there is the ~0.1 K variation in SST during a 11-year sun cycle and a ~2% change in (low) cloud cover in antiphase with TSI… I suppose that is seen in ground based measurements.

    I agree that this is probably not directly related to the huge variations in insolation over the past decades (down as well as up). But neither is there much correlation with greenhouse gases or aerosols.
    The insolation trends in Europe, as described in Philiponna ea. were mainly water vapor related (NAO-related?), dimming and brightening in the SH (Australia and even the South Pole) were/are as large as in the NH, while the aerosols are far more abundant in the NH.

    Further, I was suprised by the change in diurnal temperature over the past decades (fig. 2 in the Wild ea. article). I suppose that the smaller diurnal temperature range can’t be caused by (more reflective, less absorbing) sulfate aerosols. This is more representative for clouds and/or water vapor increases and/or black aerosols (which are assumed to give an overall warming). Thus the amplitude (and even the sign) of the aerosol influence still is very unsure, with huge consequences for GHG sensitivity…

    Comment by Ferdinand Engelbeen — 27 Feb 2007 @ 2:35 PM

  143. [[ one of the key pillars of CO2 research is that as concentrations increase the altitude of radiative reflections increases.]]

    Do you mean the emission height? Not sure what you mean by “altitude of radiative reflections.”

    Comment by Barton Paul Levenson — 27 Feb 2007 @ 4:23 PM

  144. a lawyer would say justice is based on evidence

    A court of law gives you one chance, and you are innocent until proven guilty. It’s absolutism at its worst, and thus your analogy is ludicrous.

    In science, you get to test the evidence over and over, indeed, you can create the evidence from scratch as often as you like, so skepticism is a laughably naive scientific method. Reproducibility is far more effective.

    Nobody I know of approaches a scientific result as guilty until proven innocent, what we do is read the paper and give it a chance, first. Then, if we have a problem with the result, based upon our own experience or evidence, we either attempt to reproduce the result, or if impractical, we bring our reservations to the attention of the original authors, usually by phone or email. Only as a last resort is a comment published.

    Comment by Thomas Lee Elifritz — 27 Feb 2007 @ 6:17 PM

  145. “a lawyer would say justice is based on evidence”

    Thats what a lawyer might say in his oral arguments in a trial, but its more accurate to say that the lawyer is going to present the evidence in a way that advances a favorable outcome for a client.

    Legal proceedings are a poor analogy for science, but a better one for the politics around the science. The legal system is different than the scientific method. For example science you can go and retest evidence, but if you did not limit the rehearing of evidence in the courts the system would grind to a halt.

    Comment by Joseph O'Sullivan — 27 Feb 2007 @ 6:41 PM

  146. RE #119, “Sun is the first order influence on climate. My experience tells me that water vapor is number II and at best CO2 is number III.”

    Dennis Wingo does admit the GHGs are a GW forcing, as is the sun (which even the ancients realized). Water vapor, however, is a feedback, not a forcing, due to its short time in the atmosphere — I learned that from RC a couple of years ago. And I accept the consensus that the sun is not significantly increasing its forcing at this point (until proven otherwise).

    But if the sun was contributing to the present warming, then the policy implications are that we’d have to reduce our GHGs all the more, to counterbalance its effects. And we may need to keep our fossil fuels in the ground, just in case at some future time sunshine should start declining.

    So as long as the “solar crowd” agrees that we need to greatly reduce our GHGs & actually reduces their GHGs and encourages others to do so, then their arguments are just academic & a headache to scientists who disagree with them, but no serious problem to me.

    Comment by Lynn Vincentnathan — 27 Feb 2007 @ 6:47 PM

  147. Clearly greenhouse gas emissions need to be reduced dramatically, and excess carbon dioxide ultimately will have to be scrubbed from the atmosphere, otherwise another Paleocene Eocene Thermal Maximum is inevitable, probably well within 1000 years, at the current rate of greenhouse gas emissions, and anticipating positive feedback effects.

    However, as a short term stop gap measure, to give us time to develop the technologies necessary to facilitate a favorable result, artificial aerosol emissions injected into the upper atmosphere is worthy enough of serious study. Perhaps some sort of reflective or absorptive particles could be dissolved as an additive to hydrogen rocket fuel, or oxidizer, or in jet fuel, to artificially modify the transmissive properties of the atmosphere. I admit it would be a running game to ensure the necessary radiative balance, but when all is said and done, the materials would eventually drift back to the ground, and then the natural balance might be restored. Now that we know more about aerosols and the global cooling effects, modeling of any hypothetical atmospheric additives might begin.

    On the other hand, I am of the opinion that the ultimate solution will be some sort of advanced solar technology for fixed energy applications, and hydrogen oxygen cryogenic technology for transportation, technology that would be most easily developed by a comprehensive international space colonization program, along with constantly evolving energy conservation and infrastructure modernization programs, for instance – Earth sheltered housing, etc. Then, when we cover the Earth with solar panels, we will have to consider albedo. It will always be something. When we solve one problem, there will always be others. With soon to be 9 billion people on the planet, something has to give. We just can’t keep going in the direction we are headed.

    I’m not saying complete space colonization is the answer, but it’s the attempt that will yield the solutions.

    Comment by Thomas Lee Elifritz — 27 Feb 2007 @ 7:41 PM

  148. Re#146

    I don’t think that an increased solar contribution means that we need to reduce GHG emissions even faster. As we have only one temperature record, which is the result of many influences, if the sun (or internal variations) was responsible for a higher portion of the recent warming, that means that the response (the sensitivity, not the forcing itself) to GHGs is lower, thus a doubling of CO2 (equivalents) will lead to a lower increase in temperature, which makes drastic measures less necessary.

    That doesn’t mean that we shouldn’t reduce fossil fuel use, but for other reasons: less dependancy of not so stable countries and less pollution…

    [Response: Since there isn’t any evidence that would justify increasing the estimate of the solar contribution in the past, this line of thinking is more or less moot anyway. However, it’s worth thinking about possible future solar increases. The Sun will continue ticking along doing its thing and could well go through a brightened phase in the future. Presumably such fluctuations have been going on throughout time — but for the past 2 million years never superposed with a warming trend due to CO2 as great as we have now. Thus, insofar as there are uncertainties about what the Sun is going to do in the future, what one should be worrying about is whether we will be hit with an uptick in solar forcing which, superposed with CO2, throws us past some additional climate threshold. –raypierre]

    Comment by Ferdinand Engelbeen — 28 Feb 2007 @ 2:53 AM

  149. Re #115, 126: I have found better information about the timing of warming and cooling effects of closing a coal station, from this article about switching from coal to natural gas.

    The carbon content of natural gas is only 60 percent that of coal per unit of primary energy content.

    “When the â��best guessâ�� estimates of radiative forcing are applied to global average coal and gas characteristics, the benefits of fuel switching are delayed by about 30 years,” Jain said. “The delay is caused by the reduction in sulfate aerosol emissions and increase in natural gas-related methane emissions that occurs when switching from coal to natural gas â�� creating a net warming effect…”

    However, coal and gas use also release methane, the second most important greenhouse gas emitted by human activities. During coal extraction, methane trapped in and around coal seams is released to the atmosphere. Methane also is released whenever natural gas escapes during transportation and distribution. Hence, switching from coal to gas would reduce methane emissions from coal mining, but increase natural gas-related emissions.

    Assuming the methane effects roughly cancel, if a 40% reduction in CO2 requires 30 years before a reduction in warming begins, then a 100% reduction would mean a 10 to 15 year lag in benefits. That is not too far off my original calculation.

    Comment by Blair Dowden — 28 Feb 2007 @ 7:03 AM

  150. [[I am of the opinion that the ultimate solution will be some sort of advanced solar technology for fixed energy applications]]

    I agree. I’m very excited about the newer Solar thermal electric plants. The ability to store heat in molten salts and continue running the plants at night is an answer to the people who damn solar for being “intermittent.”

    Comment by Barton Paul Levenson — 28 Feb 2007 @ 7:53 AM

  151. #146 & 148, only for the sake of argument, suppose the climate is less sensitive to GHGs and the sun is causing the major portion of the warming, we can do nothing about the sun, but we can do something about our GHGs. And whether it’s the sun or us, GW is a dangerous thing. So we have to do what we can to reduce it. Since in this scenario the climate is not very sensitive to GHGs, that means we will have to reduce even more to achieve some reduction in GW.

    But the closer truth be known, the climate is probably more sensitive to our GHGs, taking the aerosol-effect into account AND the possible positive feedbacks in the future, so in this scenario, too, we must drastically reduce our GHGs.

    Either scenario, we lose big by not reducing much.

    Comment by Lynn Vincentnathan — 28 Feb 2007 @ 10:40 AM

  152. Re #147: “Then, when we cover the Earth with solar panels…”

    Which brings up a point that I think is too often ignored by the advocates of solar power, which is that most of the incoming solar energy is already being used by plants. Cover the earth, or even a sizeable fraction of it, with solar panels, and you’ve just taken away the energy source that drives most of the biosphere.

    The same is true, in less degree, of commercial solar plants. Intercept the sunlight, and the plants underneath will die. At what point does that start causing its own environmental problems?

    Comment by James — 28 Feb 2007 @ 12:49 PM

  153. Re #149. Renewed thanks – and 10-15 years for a net negative forcing from ending fossil fuel use looks a lot better to me than 100 or more! Interestingly, even amusingly insofar as anything this serious has a funny side, the reduction in GHG emissions the UK government likes to boast about comes almost entirely from the switch from burning coal to burning gas in power stations (a switch which was motivated by cost-saving, not GHG emission reduction). Indeed if it wasn’t for this switch, UK GHG emissions would have increased considerably over the period from 1990. If your calculations are roughly correct, we’ve not yet reached net negative forcing from the change from coal to gas.

    Comment by Nick Gotts — 28 Feb 2007 @ 1:16 PM

  154. [[Which brings up a point that I think is too often ignored by the advocates of solar power, which is that most of the incoming solar energy is already being used by plants. Cover the earth, or even a sizeable fraction of it, with solar panels, and you’ve just taken away the energy source that drives most of the biosphere.

    The same is true, in less degree, of commercial solar plants. Intercept the sunlight, and the plants underneath will die. At what point does that start causing its own environmental problems? ]]

    The “sizeable fraction” necessary is less than 1% of Earth’s land surface. The plants will survive.

    Comment by Barton Paul Levenson — 28 Feb 2007 @ 3:20 PM

  155. Re #152 Space for solar energy a problem?

    Total world energy demand is roughly 1.2e13 Watt (= 12 TW). One sqm of solar panel can produce ca 24 W on average in places like Egypt (average solar radiation 200 W/sqm). Hence covering half of Egypt (500,000 sqkm of desert) would suffice to cover world energy demand.

    Solar has its practical problems, but space is not one of them. I imagine that solar will become very important in the near future.

    Comment by Dick Veldkamp — 28 Feb 2007 @ 4:14 PM

  156. Re #148, Ray’s comment: I thought we were at the high point of the solar cycle, however significant that may be. Future changes in solar output are more likely to have a cooling effect. However, at most that would be about half a watt per square meter, equivalent to a few decades of warming at the current rate.

    So if we are lucky we might get some extra time to reduce anthropogenic warming, but I would not count on it.

    Comment by Blair Dowden — 28 Feb 2007 @ 9:25 PM

  157. Just past the low point:

    Comment by Hank Roberts — 28 Feb 2007 @ 9:42 PM

  158. #136 Gavin comment : remember that a large number of us have authored papers on solar changes and possible responses

    Not only I remember… but I read you! I’ve just finished Rasmus’ book on that topic.

    #148 Raypierre comment : Since there isn’t any evidence that would justify increasing the estimate of the solar contribution in the past, this line of thinking is more or less moot anyway

    It would be interesting to know if there’s any solar influence on XXth century, in your opinion (I mean of course a response to forcing, not the natural influence day/night, seasons, etc.). After all, with 0,1 W/m2 TOA forcing 1750-2000, it should be nearly impossible to discern a distinct signature on surface temperatures. An equilibrium climate sensitivity of 0,75 K.W/m2 implies in this case a 0,075 K response, inferior to the margin error / uncertainty of instrumental measurement on the Hadley CRU database. What I miss is the nature and relative weight of forcing agents for 1750-1950 warming (because if there’s no solar trend since 1950, the solar forcing 1750-1950 is also 0,1 W/m2). Anyway, that’s off topic here, I’ll go on with my readings and try to understand.

    Comment by Charles Muller — 28 Feb 2007 @ 11:23 PM

  159. Re the long-term solar influence:

    What Raypierre alludes too is the long-term influence of solar. While there is less doubt about the variation in energy (TOA) over the last two cycles (+/- 0.5 W/m2), there still is a lot of discussion about the influence of solar in the longer past (and even over change of the last cycle minima). What is clear, is that we now are at an exceptional high level of solar activity. There is a lot of discussion going on in the solar community what the next cycle will bring (some think still high, others predict a much smaller maximum).
    In general the change in solar forcing from the LIA to present is thought to be in the order of a few times the variation over one cycle. How much that change influences temperature is the most controversial point and is highly dependent of the reconstruction used.
    Reconstructions with a low variation (like MBH98/99) indicate a small influence of solar, as volcanic eruptions cause a cooling of (at maximum) 0.1 K over the past 600 years, leaving 0.1 K for natural (mainly solar) influences. Reconstructions with high variation (like Moberg, bore holes) have the same influence of volcanic, but up to 0.7 K for natural.

    This result of this is that in the first case, solar changes had a small influence on the temperature increase of the 20th century (10-20%) and thus in the future, in the second case, it is up to 50% (as Scafetti tried to explain in a previous discussion). The rest of the warming is mostly from GHGs, as far as internal natural cycles are not interfering. I am pretty convinced of the high influence of solar, but that is only possible if responses to solar forcing differs from responses to GHGs (and are much higher), which is possible, as solar (and volcanic) have their highest influence in the stratosphere, while GHGs (and anthro aerosols) have their highest influence in the (lower) troposphere. That is my difference in opinion with Raypierre and Gavin (and most climate modellers), who see only small differences in sensitivity for the four main forcings…

    If solar has more influence than currently implied in models, that means that we may have more time to change to non-fossil fuels, as for the same amount of CO2, the resulting temperature increase is lower…

    Comment by Ferdinand Engelbeen — 1 Mar 2007 @ 2:47 AM

  160. Re #157, 158: Perhaps my figures are a little out of date; they are from Lean and Rind 1998. The recent IPCC SPF states “Changes in solar irradiance since 1750 are estimated to cause a radiative forcing of +0.12 [+0.06 to +0.30] W m-2, which is less than half the estimate given in the TAR.”

    Solar effects seem to be a falling star.

    Comment by Blair Dowden — 1 Mar 2007 @ 7:26 AM

  161. [[If solar has more influence than currently implied in models, that means that we may have more time to change to non-fossil fuels, as for the same amount of CO2, the resulting temperature increase is lower… ]]


    For the hundredth time: the extent of the Solar forcing has no effect on the extent of the CO2 forcing. They are independent.

    Solar can’t be driving the present global warming because A) the Sun’s luminosity hasn’t varied noticeably in 50 years as measured by satellites; B) increased sunlight would heat the stratosphere, and the present stratosphere is cooling; and C) increased sunlight would heat the equator more than the poles, whereas we are now seeing much greater warming at high latitudes.

    Comment by Barton Paul Levenson — 1 Mar 2007 @ 8:12 AM

  162. #161 Barton, I don’t agree with your three assertions, but please correct me if I’m wrong.

    A) Solar total and spectral irradiance is measured by satellite since 1979, not 50 years. And there’s still a debate for the interpretation of cycle 21-23 data.

    B) For this 1979-2006 period, the ozone depletion is supposed to greatly influence the stratos. temperature trends, as measured by satellites in lower layers (14-22 km). Anyway, the 1979-2006 TSI trend is weak if any, so you’re not supposed to get a clear signature here, nor in upper strato. layers 22-50 km.

    C) I sea no reason for a major solar influence on Equator surface temperatures rather than mid and high latitudes ones. Models usually show that climate change of the past are more pronounced poleward, whatever the forcing. Heat in intertropical zone is redistributed either by convection in upper layer or by oceanic / atmospheric circulation in higher latitudes. (Maunder Minimum, whose everybody agree it was partly solar induced, was mainly marked on NH lands, not on Tropics, for example).

    For the first point, I’m not sure sun doesn’t influence CO2 forcing, or at least climate feedbacks to CO2 forcing. For example, CO2 effects won’t be exactly the same in a 1360 or 1365 W/m2 TSI situation, so far the (relative) forcing of GHGs depends on water vapour concentrations, emissivity temp. of each layer, ocean and vegetal carbon sink in response to luminosity, etc.

    Comment by Charles Muller — 1 Mar 2007 @ 11:35 AM

  163. [[I sea no reason for a major solar influence on Equator surface temperatures rather than mid and high latitudes ones. ]]

    Lambert’s Law.

    Comment by Barton Paul Levenson — 1 Mar 2007 @ 3:05 PM

  164. #163 AFIAR, there’s a solar signal in tropical atmosphere of minimum-to-maximum amplitude of a cycle, mainly observed in high to mid troposphere. But we’re speaking here of solar forcing, not relative insolation, that is long term effects of a radiative imbalance on climate. And I never read that climate models expect a pronounced tropical response to multidecadal TSI increase / decrease. Any reference for that? If you look at IPCC 2001 “6.14 The Geographical Distribution of the Radiative Forcings”, you see that GHGs direct forcing is more pronounced in low than in high latitudes. Do you expect a maximal response to GHGs forcing at 30°N / 30°S?

    Comment by Charles Muller — 1 Mar 2007 @ 9:48 PM

  165. My bad — that should have read Lambert’s cosine law. The other Lambert’s law wouldn’t be relevant, of course.

    Comment by Barton Paul Levenson — 2 Mar 2007 @ 8:00 AM

  166. Barton, in addition to what Charles said, the discussion is not about forcings, it is about sensitivity, or the effect of forcings + feedbacks on temperature. While forcings are more or less known for GHGs and recently for solar strength (still with a lot of discussion), feedbacks may be different, especially for cloud formation, which scientific understanding is very low. And responsible for much of the wide range in projection for 2xCO2. 2xCO2 without feedbacks only increases global temperature with 0.85 K, the rest is thought to be from water vapor feedback and other feedbacks (ice albedo, clouds). Thus if the sensitivity (and the forcing for the pre-satellite period) for solar is higher than implemented in current GCM’s, that is at the cost of the sensitivity of GHGs (not the forcing) and the sensitivity and/or forcing of aerosols, as these work in tandem.

    Besides the stratospheric effects on climate (variations in jet stream position and rain over the US and South Europe), global cloudiness varies with +/- 2% over the 11-year cycle. Solar has its highest energy effect in the tropics (but the heat is redistributed towards the poles), while the effect of GHGs is more evenly spread over the globe.

    Ocean heat content increase was highest in the subtropics, where a reduction in cloud cover was measured (+ 2 W/m2 more insolation in 15 years time over the whole tropics). If the latter is internal natural or solar induced, that is an unsolved question…

    Comment by Ferdinand Engelbeen — 2 Mar 2007 @ 1:34 PM

  167. Funny about the figure given for co2 logevity. You say a century while the figure commenly given is several centuries. One century would mean that co2 molecules emitted before 1906 would have left the atmosphere by now. What is the correct span?

    Comment by David Price — 2 Mar 2007 @ 4:30 PM

  168. [[2xCO2 without feedbacks only increases global temperature with 0.85 K,]]

    1.2 K according to Houghton. I’m familiar with feedbacks, too.

    Comment by Barton Paul Levenson — 2 Mar 2007 @ 4:48 PM

  169. It is well known that the warming of sea surface temperatures amplifies energy transfer to the atmosphere which in turn, increases the frequency and power of hurricanes. Would it then be right to assume that this can also cause a corresponding increase in the transfer of sea salt to the upper atmophere? I have read accounts of whole schools of fish being drawn aloft and dumped many miles away.

    Comment by Michael Ellson — 5 Mar 2007 @ 10:40 PM

  170. Oh, my, Google’s utterly bogus on this one:
    Scholarly articles for: whole schools of fish being drawn aloft and dumped many miles away
    The adventures of Tom Sawyer – Twain – Cited by 42
    Out of the Night – Valtin – Cited by 3
    Harry Potter and the half-blood prince – Rowling – Cited by 11

    Comment by Hank Roberts — 5 Mar 2007 @ 11:07 PM

  171. Re #167: The 100 year lifetime for CO2 residence time in the atmosphere is rather arbitrary. In 20 years almost half of it is gone, in 100 years 25% of it still remains, and in 100,000 years 7% is still there. See the graph on this page.

    Comment by Blair Dowden — 6 Mar 2007 @ 7:13 AM

  172. In response to #169, you are dead on about one thing: hurricanes do have the ability to convectively transport aerosols up away from the boundary layer to the free troposphere. (sea salt in cirrus clouds in mid-America). Also, evidence has shown that aerosols from tropical fires reach the upper troposphere via deep tropical convection, where they are free to get swept in the strong upper level winds, and carried great distances. (tropical aerosols and convection) However, I am not sure that the assumption that warming-induced increases in hurricane intensity will make a big impact on the amount of aerosols in the troposphere, mostly because over the ocean (where hurricanes are) sea-salt aerosols are abundant, and that in order for them to get swept into the hurricane in the first place, they must have been made airborne by some other process. It is plausible to associate that “other process” to increased wave breaking in hurricanes, but I have a hard time believing that this would transport significantly more sea salt to the atmosphere.

    But your assumptions are definitely valid, and I think they play into a more dire problem: tropical forest fires. Anthropogenic forest fires have increased dramatically in recent decades, especially in the tropics. The input of aerosols from these fires is enormous, and can result in a multitude of climate responses. Understanding the transport of aerosols to the upper troposphere via convection is important, and I think more needs to be understood of the indirect effects of aerosols on clouds. One recent study has shown that subtropical absorbing aerosols (soot) actually decreased cloud cover (specifically trade cumulus) by heating the top of the boundary layer. (reference Ackerman, et al., 2000) This effect on aerosols would not mute the ongoing effects of CO2, but rather enhance it. Any thoughts on this?

    Comment by Mike Tosca — 8 Mar 2007 @ 2:54 AM

  173. I have a layman’s question. At what concentration does CO2 becomes a warming agent?

    Comment by Robert Smith — 9 Mar 2007 @ 3:19 PM

  174. Re 134,

    That is nuts what you said. An engineer is creationist eh? You know as a guy with a Master’s in Electrical Engineering and a very strong minor in modern physics I take exception to that. You simply don’t know your rear from your elbow.
    I used to work the Los Alamos National High Magnetic Field Laboratory. (Only dumb people work there, you know guys from MIT,UFL,FSU, Georgia Tech, Caltech etc.etc.) I met a Nobel Prize winning physicist there and he was a lot more humble than you are and made some important discoveries in his time there. I also met a lot of physicsts that could not find their way to the bathroom. Should I generalize about physicists as well? Would not that make them look very stupid?

    Comment by Jim — 9 Mar 2007 @ 5:01 PM

  175. re: 174. Your ad homs aside, all of that you stated clearly indicates that you are not an expert in climate models, science and similar research. As opposed to the literally thousands of climate scientists around the world and essentially every major scientific society around the world who agrees regarding the influence of man-made GHG emissions on climate. And who have published their research in peer-reviewed journals.

    Comment by Dan — 9 Mar 2007 @ 5:34 PM

  176. Dan,

    Your comments aside, that was not the point. Never claimed to be a climate scientest and I don’t comment about them either. You clearly can’t read well because I don’t comment often and it is on subjects I know something about. I do know power systems, digital design (mostly dealing with ASIC design), communcations, signal processing and such as that. Do you? If not then keep silent about subject matters that you also know nothing about. In any case that was directed at Barton. If you have guilty heart fine. Also Dan are you an “expert”, or are you a self educated google user?
    Further, it clearly was not for fun. The generalization made by Barton is that engineers were not well educated in science and that is simply false.

    Comment by Jim — 9 Mar 2007 @ 7:50 PM

  177. [[I have a layman’s question. At what concentration does CO2 becomes a warming agent? ]]

    Theoretically, at any concentration, but in practice it would have to be several ppm before it could make changes measure in tenths of a degree.

    Comment by Barton Paul Levenson — 10 Mar 2007 @ 10:55 AM

  178. [[That is nuts what you said. An engineer is creationist eh? You know as a guy with a Master’s in Electrical Engineering and a very strong minor in modern physics I take exception to that. You simply don’t know your rear from your elbow.]]

    I don’t think you understood what I said; perhaps I phrased it poorly. It has been my experience that engineers are over-represented among creationists and Velikovsky followers, and I attribute that to their believing that an ability to manipulate equations makes them scientists. But you can’t get “most engineers are creationists” from “some creationists are engineers.” It would be a non sequitur.

    Comment by Barton Paul Levenson — 10 Mar 2007 @ 10:58 AM

  179. I’m sorry but

    “It didn’t surprise me to find out that a lot of creationists and believers in Velikovsky’s astronomy are engineers. They think if you can manipulate equations, that makes you a scientist”

    Will make any engineer angry. In any case engineering is built on physics and mathematics and to say that engineers are not scientists is silly. In any case as a guy with a couple of classes short of a physics degree to get my Eletrical Engineering B.S and M.S it is even more infuriating. I could say (truthfully too!) that most of the visiting physcists at the Los Alamos National High Magnetic Field Laboratory were severly lacking in common sense and were trapped by in-the-box thinking. In essence they could not make anything work. I believe that physicists have great ideas but can’t apply them or make them work in the real world. Whereas engineers were more interested in applying science to the real world in order to obtain real results. At least that was my experience at LANL NHMFL.

    Comment by Jim — 10 Mar 2007 @ 6:01 PM

  180. “It didn’t surprise me to find out that a lot of creationists and believers in Velikovsky’s astronomy are engineers. They think if you can manipulate equations, that makes you a scientist”

    Will make any engineer angry.

    Unfortunately, it also happens to be true.

    The creationist/intelligent design camp is full of engineers who claim that engineers are better trained to understand biology than evolutionary biologists.

    Don’t believe me? Visit Uncommon Descent and read a few threads there.

    Comment by dhogaza — 11 Mar 2007 @ 7:34 PM

  181. [[to say that engineers are not scientists is silly.]]

    Engineers are not scientists. They do not pursue abstract knowledge through observation and experiment and publish in peer-reviewed journals. They develop products.

    Comment by Barton Paul Levenson — 12 Mar 2007 @ 8:11 AM

  182. Barton,

    That is simply wrong.
    I worked with a lot of physicists and they had their eye on developing products/process with their ideas. Materials science and biophysics come to mind as immediate examples of this. To say that what makes a scientist is to not have a wish to commercially develop their ideas is naive in the extreme. (I guess all of those royalties from patents that professors and universities recieve is from charity eh?) You sound almost religous about a scientists intentions!

    In any case as a grad engineering student I published papers that were submitted to peer review all of the time. My professors were so much more so. They were constantly going to conferences and reviewing other’s works, inventing new process and new ideas. (The “peers” were from Comp Sci, Mathematics, Physics, etc.etc.) I say again Engineers are taught physics just like physicists are and just as well. Lot of guys in the same classes you know, same teachers. And how different can EM field mechanics, fluid dynamics, and thermodynamics be between engineers and physicists?

    [inflammatory language edited–please watch the flaming]

    Comment by Jim — 12 Mar 2007 @ 10:41 PM

  183. Water vapor feedback may hold a more significant unknown. The level of feedback due to visible absorption of solar radiation is not well understood and not well accepted. Reports have suggested that the feedback is stronger than calculated, and Arking has suggested some time ago that shortwave quadratic dependent water absorption is the explaination. Recent as yet unpublished measurements support his theory.

    Comment by James Hargrove — 14 Mar 2007 @ 9:35 PM

  184. Given the uncertainty about current aerosol levels (see e.g., how do we know that aerosols largely accounted for the global cooling of 1940-1980?

    Comment by Nick — 20 Mar 2007 @ 6:07 AM

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