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  1. Clearly stated. Thank you.

    Comment by David B. Benson — 21 Apr 2009 @ 6:21 PM

  2. Thank you for the excellent post Dr. Shindell.

    Can you (or someone at RC) please provide the best type of sources used for assessing the time-evolution of aerosol emissions (or forcing) over the 20th century (particularly 1900 to roughly mid century-ish where records are likely poorly constrained). I’d imagine there’s good relaince on ground radiation measurements after subtracting the change in TSI. I know the ice core record shows up tracking the sulfate changes fairly well, but the paper by Stern and Kaufmman on “Estimates of Global Anthropogenic Sulfate Emissions 1860-1993″ was the only paper I’ve really seen on the subject, which is fairly old.

    Comment by Chris Colose — 21 Apr 2009 @ 6:21 PM

  3. Thanks very much for taking the time to give this!

    I’ve been trying to talk sensibly about your paper at a large physics discussion forum, at “”. I write there under the name “Sylas”. The thread of discussion is at Only dirty coal can save the Earth. (I didn’t pick the title; I only joined in at message 11!)

    Physicsforum is not intended for fringe or crank science, but it is open to all comers. To try and manage the obvious difficulty, a special requirement has been laid down that only peer reviewed sources may be used in the Earth science section, where the physics of climate is often discussed.

    I hope I’ve been representing this work appropriately… I think so. (And if anyone can correct places I’ve misunderstood things, join in!) I’ll also put a link there for this article, as there are lots of folks who will, I think, be interested to see what Drew has to say on this directly. It’s certainly useful for me!

    Thank you! — Sylas

    Comment by Duae Quartunciae — 21 Apr 2009 @ 6:51 PM

  4. Good Post

    Comment by EL — 21 Apr 2009 @ 7:35 PM

  5. This may be nitpicking and doesn’t affect the main thrust of the contribution,but, I believe, that the 0.6 and 2.4 W/m^2 figures in the IPCC AR4 are positive in sign and refer to the range in the total net anthropogenic forcing.

    Comment by Lawrence Brown — 21 Apr 2009 @ 8:26 PM

  6. Dr. Shindell,

    A fascinating post to compliment a fascinating paper. I’m curious to know if anyone has modeled the expected net forcing of projected global aerosol reductions over the next century (due to growing prosperity and our friend Kuznetz) taking into account changes in both sulfate aerosol and black carbon forcing. If I recall correctly, the AR4 WGIII projected a mean 50% decline in annual global aerosol emissions, though there was considerable uncertainty due to the wide range of socioeconomic scenarios examined.

    My back-of-the-proverbial-envelope calculations awhile back yielded 0.36 degrees C warming due to a 50% decline in sulfate aerosols (assuming a current anthropogenic SO2 combined direct and indirect forcing of -0.83 Wm-2 and a climate sensitivity of 0.87 K), though this left out any calculation of changes in black carbon forcings.

    Comment by Zeke Hausfather — 21 Apr 2009 @ 8:56 PM

  7. This confirms what I’ve always suspected. Air pollution camouflaged the
    effects of higher GHG until efforts were made to reduce it. Now imagine what
    will happen if/when China shuts down its coal fired generators.
    The net forcing will be higher for years as more rays reach the ground
    and are trapped by CO2. What is the break even point after such a scenario?
    Probably a decade at least.

    Comment by Mike Hilson — 21 Apr 2009 @ 8:57 PM

  8. Shouldn’t the older models have captured these issues? It seems pretty clear to me that this should have been built in already.

    Comment by John Lang — 21 Apr 2009 @ 10:00 PM

  9. Lawrence Brown at #5: the aerosol forcings in IPCC 4AR are in the range -0.6 to -2.4

    Have a look at table 2.12, on page 204 of the WG1 report.

    It doesn’t actually quote the total aerosol there as a single range, but gives rather:
    -0.5 [-0.4, +0.4] (Total direct aerosol)
    -0.7 [-1.1, +0.4] (cloud albedo (indirect) effect, all aerosols)

    You add uncertainties as square root of the sum of squares. Hence the combined total aerosol there is

    -1.2 [ -1.17, +0.57 ]

    which to the single figure accuracy being used is -2.4 to -0.6.

    The total combined anthropogenic forcing is quoted at the head of this table, and it is 1.6 [-1.0,0.8]

    That gives 0.6 to 2.4

    I had never noticed this co-incidence before! But it is just a co-incidence. The graph in figure 2.20 on the previous page shows what is going on. As well as this rather poorly constrained aerosol forcing, there’s the much more accurately known greenhouse forcing, of +2.63 [-0.26,+0.26], which when added to the aerosol effect, just shifts it all across a bit.

    One of the great things about Shindell and Faluvegi is that it points a way to reduce the uncertainty of the aerosols. The best estimate global aerosol effect, however, remains about the same (-1.3 compared with -1.2)

    Comment by Duae Quartunciae — 21 Apr 2009 @ 11:20 PM

  10. Soot has a positive forcing

    Comment by Eli Rabett — 21 Apr 2009 @ 11:41 PM

  11. I know it is off topic, but I think the recent paper by Romps and Kaung
    which purports to show that increases in tropical cyclone activity may be responsible for significant increases in stratospheric humidity. If this pans out, then it represents a previously unknown or underappreciated (at least to a layman like me) positive feedback mechanism. My gut feeling, is that stratospheric water vapor is so low that it wouldn’t have a strong warming effect, unless there was cloud formation -but I am not equiped to answer the question as to how strong such a feedback effect might be.

    Perhaps this could be the topic of a future discussion?

    Comment by Thomas — 21 Apr 2009 @ 11:54 PM

  12. Mike @7
    I tend to agree that China will have a big effect but rather than shutting down their coal, I think its far more likely they’ll place air pollution controls similar to what we did during the 70’s to improve local and regional air quality.

    The aerosol articles have been excellent.

    Comment by Ray Menard — 22 Apr 2009 @ 1:55 AM

  13. John what makes you think the models don’t include these things?

    Comment by Mark — 22 Apr 2009 @ 2:39 AM

  14. Very interesting indeed! What happens with the sea ice response as aerosols are added in?

    For more on why reducing black carbon aerosols is a good idea:

    Black Carbon Pollution Emerges As Major Player In Global Warming, San Diego CA (SPX) Mar 25, 2008
    Black carbon, a form of particulate air pollution most often produced from biomass burning, cooking with solid fuels and diesel exhaust, has a warming effect in the atmosphere three to four times greater than prevailing estimates, according to scientists in an upcoming review article in the journal Nature Geoscience.

    Scripps Institution of Oceanography at UC San Diego atmospheric scientist V. Ramanathan and University of Iowa chemical engineer Greg Carmichael, said that soot and other forms of black carbon could have as much as 60 percent of the current global warming effect of carbon dioxide, more than that of any greenhouse gas besides CO2. The researchers also noted, however, that mitigation would have immediate societal benefits in addition to the long term effect of reducing greenhouse gas emissions.

    There’s also the negative correlation between black carbon aerosols and precipitation:

    This has been widely noted, for details see:

    In this study, observed precipitation, MODIS data and meteorological sounding data over eastern central China were analyzed. The result shows that the precipitation in this region is significantly reduced during the last 40 years and this reduction of precipitation is strongly correlated to the high concentrations of aerosols.

    Comment by Ike Solem — 22 Apr 2009 @ 3:14 AM

  15. So due to the seemingly very large error bars on these aerosols, thier forcing potential could still be casting a doubt over the forcing of GHG?

    The global mean preindustrial to present-day aerosol forcing we calculate is -1.31 +- 0.52 W/m2, consistent with the IPCC AR4 range of -0.6 to -2.4 W/m2.

    This is slightly disoncerting for it does not and seemingly cannot let us know the true forcing we are experiencing for it could be low or high relative to GHG forcings and the uncertainty gives ammunition to the skeptics once again I suppose.

    Comment by pete best — 22 Apr 2009 @ 4:18 AM

  16. “So due to the seemingly very large error bars on these aerosols, thier forcing potential could still be casting a doubt over the forcing of GHG?”

    Uh, casting uncertainty.

    Is that uncertainty significant?

    Is the uncertainty reason to avoid change?

    Why did you not ask these questions? A skeptic would. Someone avoiding having to think about it will find anything or even make it up.

    Comment by Mark — 22 Apr 2009 @ 6:34 AM

  17. Re #15 pete best: sigh, yes. But remember, uncertainty is just another word for risk. Contrary to what the “skeptics” seem to believe, it doesn’t respond to prayer :-(

    Comment by Martin Vermeer — 22 Apr 2009 @ 7:07 AM

  18. If black carbon has a significant positive forcing, is this good news or bad? Are there quick fixes for cutting soot while we try to figure out how to cut CO2? Or is it just bad news because some mitigation efforts (like promoting diesels over petrol cars) will turn out to be unhelpful?

    Comment by CM — 22 Apr 2009 @ 7:35 AM

  19. Re #16 and #17, Its ok guys, I am just worried that the sensitivity of the climate is more so and hence more warming is going to happen than that predicted by the IPCC who is a very conservative body whose reports are not entirely scientific due to the political angle on the report.

    I fully accept that the error bars are within scientific tolerance, I just worry about the sensitivity a little bit. We don’t need even more warming now do we, we are going to get anough already and even more come another few decades of emissions.

    Comment by pete best — 22 Apr 2009 @ 7:37 AM

  20. Hi Pete at #15: There is indeed a substantial uncertainty in the total forcing, and it is mostly from uncertainty on cloud and aerosol effects.

    No, this does not cast any doubt whatsoever on the greenhouse contribution, which remains one of the best defined and understood forcings involved. It can be calculated from first principles, using the same well established physics that applies for any calculation of electromagnetic transmission through a mix of gases. The methods work for the Sun’s photosphere, for a laboratory gas cell, or the Earth’s atmosphere.

    The uncertainty of the well mixed greenhouse forcing is about 10%, and that doesn’t depend in the slightest on the uncertainty with aerosols. They are different things.

    There’s no cause to be “disconcerted” by this, and neither is there any reason to obscure the real uncertainties and open questions that scientists are working on. We certainly don’t want to pretend that knowing the greenhouse forcing is the same as knowing all about climate!

    I agree with you that any uncertainty gives ammunition to so-called skeptics, but that’s only because they are not skeptics at all. Many of the these folks turn out to be some of the most credulous and naive simpletons on the planet, who’ll enthusiastically embrace any argument, however ridiculous, as long as it can be spun into denial of anthropogenic global warming.

    That shouldn’t make a difference for the rest of us, as we try to explain the various aspects of real climate science for an interested public.

    Comment by Duae Quartunciae — 22 Apr 2009 @ 8:26 AM

  21. Papers (about ten years ago? in PNAS?) by Hansen suggested that shutting down black carbon and methane emissions would buy time to start limiting CO2 emissions, which is much harder. We (eliminated water wastes) away the opportunity. It is a necessary step forward now but we will pay the opportunity costs as the effect will not be as large given the rise in greenhouse gas forcing.

    Comment by Eli Rabett — 22 Apr 2009 @ 8:45 AM

  22. Re #9: I stand corrected. I was taking my numbers from figure SPM.2. Radiative Forcing Components, of the Summary for Policy Makers report of AR4. which gives numbers of 1.6[0.6 to 2.4] for total net anthropogenic forcing. Thank you for the clarification.

    Comment by Lawrence Brown — 22 Apr 2009 @ 8:59 AM

  23. I don’t get it.
    1.1 + or – .8 gives a range of .3 – 1.9 C for BC contribution
    1.5 + or – .3 gives a range of 1.2 – 1.8 C for total artic warming.

    Doesn’t this mean that there is a statistical chance that the entire total artic warming is due to BC?

    If that is the case – than doesn’t that mean that there is a statistical chance that zero % of the artic warming is due to C02?

    Comment by RickA — 22 Apr 2009 @ 10:14 AM

  24. Duae,

    There are plenty of reasons to be diconcerted. The totality of issues which indicate uncertainty should not be avoided while minimalizing a single apsect. Neither should you be more concerned about giving ammunition to skeptics than you are about the science.
    There is much to be skeptical about despite your opinions.


    Why don’t you ask questions? A skeptic would.
    Especially when it comes to the climate models.

    Someone avoiding having to think about it will find anything or even make it up.

    There are severe problems with AGW and the swarm of false claims being made by people at all levels.

    I am concerned. Why aren’t you?
    As an OSU professor and researcher Jane Lubchenco made false claims that ocean dead zones were linked to AGW.
    As the new head of NOAA Lubchenco said she wants to establish a climate information service modeled on the National Weather Service because Dr. Lubchenco “believes climate models are now sufficiently “robust” to help scientists start to do the same with climate, to help businesses, elected officials and regulators make good decisions on issues like where to put buildings or roads or wind farms.”

    “It is no longer enough to know what the wind patterns were for the last hundred years,” she said. “You want to know what they will be for the next hundred years — and they undoubtedly won’t be the same. So there are huge opportunities to provide services to the country.”

    Absolutely amazing. A new National Climate Service will soon be telling us where to put roads, buildings and wind farms 100 years out?

    Give me a break. There is no such ability in the climate models at all. None. Jane made that up.

    Will the models tell us it won’t be windy where windmills are now? Laughable.
    Then we have Thom Hartman saying on the air this week that if we don’t act fast the earth will become uninhabitable for humans and all other living creatures. Laughable.
    He said the MWP was local and limited to northern Europe and Greenland. Nonsense.
    Steven Chu is warning of increased hurricanes.
    Nancy Skinner says more category 5 hurricanes will be hitting the USA.

    On and on and on.

    And you’re claiming skeptics make up things?

    [Response: They do. – gavin]

    Comment by John H. — 22 Apr 2009 @ 10:55 AM

  25. Very nice post. The clear explanation regarding the masking effect of cooling aerosols was especially nice to see.

    I wonder how much is missed when models largely focus on TOA radiative forcing changes. Light-absorbing black carbon does not usually alter the TOA forcing much, but causes large changes in the distribution of radiation through the atmospheric column. It warms the lower atmosphere while cooling the surface (i.e. dimming). You can get at some of this by looking at changes in surface temperature, as you have done, but I’m wondering if you could comment more about what can be missed by just looking at TOA forcings.

    Also, I’m afraid I haven’t had time to read the original paper. In your model is black carbon treated as always externally mixed from sulphate?

    Comment by Ryan Sulivan — 22 Apr 2009 @ 11:34 AM

  26. #24 John H.

    You’re funny, thanks for the laugh, …but it is way past April fools???

    Comment by John P. Reisman (OSS Foundation) — 22 Apr 2009 @ 11:46 AM

  27. John H wrote: “There are severe problems with AGW …”

    I’m skeptical of that claim. What is your evidence? Evidence that hasn’t already been thoroughly debunked, that is.

    Comment by SecularAnimist — 22 Apr 2009 @ 11:50 AM

  28. Re: #24

    Gavin (inline),

    You seem to have ignored all but the last sentence of his post, or perhaps you failed to grasp his point: What isn’t being stapled onto AGW Theory and being treated as though it deserves the same high confidence?

    There is no significant difference between “making things up” and being deluded in your thinking. The first person knows they’re wrong and the second person doesn’t, but they’re both wrong.

    [Response: Does it really need to be explicitly stated that making things up is wrong? Please give me some credit. – gavin]

    Comment by Walt Bennett — 22 Apr 2009 @ 1:00 PM

  29. Re: #27


    He didn’t say there are severe problems with “AGW Theory”, he said there are severe problems with AGW as a propaganda tool, and he listed several of his concerns.

    The claims grow wilder and yet somehow more certain. If you don’t have a problem with that trend: Why not?

    Comment by Walt Bennett — 22 Apr 2009 @ 1:04 PM

  30. Walt, the reason why AGW is bad as a propoganda tool is that the facts are being used to promote it.

    And sometimes the facts don’t give a simple message.

    Anti-AGW doesn’t need to use facts, so they can ignore any that don’t stay “on-message”.

    Mind you, that’s not what the post said, is it. It said “problems with AGW theory”.

    Comment by Mark — 22 Apr 2009 @ 1:10 PM

  31. Walt Bennett wrote: “The claims grow wilder …”

    None of the claims that John H. referred to seem particularly “wild” to me.

    The claim that climate models could be useful in planning new infrastructure? What is “wild” about that? Surely it will be helpful to know where water supplies are likely to dwindle, or where coastlines are likely to be inundated, or where permafrost is likely to melt, and climate models can help to tell us those things.

    The claim that unmitigated global warming could render the Earth “uninhabitable”? We have evidence suggesting that CO2 increases from natural causes in the past, which were slower than today’s anthropogenic increase, caused massive global extinctions. And given what is known and observed about the ongoing effects of AGW, it is not difficult to envision mechanisms (e.g. large-scale die-off of forests, ocean acidification, methane releases from thawing permafrost and clathrates) by which that could happen again. Sorry to say, there’s nothing “laughable” about that.

    The claim that the so-called Medieval Warm Period was “local and limited to northern Europe and Greenland”? That’s not “nonsense”, as anyone capable of reading Wikipedia would know.

    The claim that global warming will lead to more powerful hurricanes? That’s mainstream climate science. Nothing “made up” about it.

    John H. obviously doesn’t like these “claims”. But he “rebuts” them with adjectives and attitude, not with substance.

    Comment by SecularAnimist — 22 Apr 2009 @ 1:52 PM

  32. Re: John H. #24 “There are severe problems with AGW and the swarm of false claims being made by people at all levels.

    I am concerned. Why aren’t you?”

    Oh, I’m concerned. I’m concerned that “skeptics” lie. I’m concerned they focus on temps because that is the only area that has any wiggle room for them to make stuff up. I’m concerned that they never deal with Arctic sea ice (too obvious), but can’t say enough about Antarctic sea ice because it’s more stable, which allows them to lie and claim there’s nothing to worry about.

    I’m concerned that the polls and interviews of late indicate climate scientists are scared and are far more pessimistic than their public pronouncements indicate.


    Comment by ccpo — 22 Apr 2009 @ 2:17 PM

  33. Re: #28 inline,


    I suspect that you are severely overworked, because you also misunderstood my point as well.

    Which was: the debunkerati do not own the copyright with regard to stretching information, to wit: a lot of potential climate change is being stapled onto AGW theory as though it carries the same weight.

    This was, I believe, the original commenter’s point, and it is one I have also been making for a long time, now.

    We must be careful to all remain skeptics, especially of new information. Yes, most of us accept AGW Theory as well developed and likely to be correct (within its error boundaries, of course); but we have no business saying with confidence what effect this will have on wind currents, ocean currents, storm activity or local changes.

    It’s clear that many people miss that point, thus it bears repeating.

    Comment by Walt Bennett — 22 Apr 2009 @ 2:48 PM

  34. Re: #31


    I believe my response to Gavin addresses your comment as well.

    I believe that we are observing a phenomenon here at RC and probably elsewhere:

    People have become convinced that AGW is real and has a great deal of momentum. Thus, the time for action is upon us, and yet the world seems slow to grasp this, making the situation even more desperate.

    The more information we get (“rivers are slowing”; “spring starts sooner”; “Arctic ice is at a historical low”) the more convinced we become that we must really act in a meaningful way as soon as possible.

    We start throwing this anecdote and that anecdote at the skeptics, as if to say: “Are you convinced now? (THROW.) How about now? (THROW.) Now?”

    And the more the skeptics reply: “I don’t see the hard line of evidence from AGW Theory to this factoid,” the more we look for things to throw at them, as if the sheer number of things we can find to throw at them ought to finally, at last, convince them.

    It won’t, and it shouldn’t.

    Much of what we are learning has no meaningful context. We don’t know precisely what causes it; we don’t know if it is short or long term; we don’t know if the eventual effect will be positive of negative with regard to global temps. What about any of that would make a skeptic stop being skeptical?

    It has always been and will always be problematical to point to individual observations as evidence of AGW. It remains enormously problematical to predict future effects of AGW.

    We aren’t going to win the argument by taking short cuts. We aren’t going to win it by convincing skeptics to be less skeptical.

    We have to find a common dialog and learn to understand each others’ point of view. Most of you in here have NO INTEREST AT ALL in that.

    And so, you will never get your point across.

    Comment by Walt Bennett — 22 Apr 2009 @ 2:56 PM

  35. Re:#34

    Walt, it seems to me you wish to discuss public policy, and have chosen a scientific forum to do so. As a layman who comes here to read about the science, it seems that when you say;

    “We have to find a common dialog and learn to understand each others’ point of view. Most of you in here have NO INTEREST AT ALL in that.”

    Perhaps it is you who has no interest in understanding the context of this forum?


    Comment by Pete Wirfs — 22 Apr 2009 @ 3:48 PM

  36. Nice paper and excellent post !

    Just surprised again (see my post #174 on the former item) that there is no comment about the following clarification:

    “A big uncertainty is still the influence of unforced internal variability, which we estimated from coupled ocean-atmosphere climate runs. Though that contribution is large, it was still not large enough to account for many of the mid-latitude and Arctic temperature trends without including aerosol forcing. For many cases, the influence of aerosols and internal variability were comparable in size. Though the influence of internal variability leads to a substantial uncertainty range in our results, they are nonetheless useful as other techniques of estimating aerosol forcing of climate have comparably large or larger uncertainties.”

    At a recent European Geophysical Union meeting (not this year), there were particular sessions about aerosols and Northern Hemisphere modes of variability. I attended both and was astonished to see that both scientist communities had the (only) explanation for the increasing surface warming over Europe since the 1970s: a change from regional (rather than global) dimming to brightening on the one hand, a trend in the North Atlantic Oscillation (a well-known regional mode of internal climate variability) on the other hand. While both communities were convinced of the AGW contribution to the observed temperature evolution, they were apparently ignoring each other !

    I am therefore very grateful to Drew Shindell for his important clarification and conscious that the study does not aim at providing very detailed regional estimates of aerosol forcings.
    Nevertheless, I’d like to know how confident Drew is on his estimate of unforced internal variability based on coupled GCMs ? Has he looked for example at the 20th century multi-decadal rainfall variability over tropical land and compared the GCM results with gridded observations ? This is not directly related to surface temperature but suggests (if my memory does not play a trick on me) that current GCMs could strongly underestimate the magnitude of multi-decadal climate variability.

    Am I right ? Even if I am, Drew’s paper is excellent and provides an original technique for estimating the aerosol forcing… but it might be interesting to pay a particular attention to the regions where internal climate variability is supposed to be low. Does the Arctic belong to this category ?

    Comment by Hervé — 22 Apr 2009 @ 4:09 PM

  37. Mr Bennett writes:

    “We start throwing this anecdote and that anecdote …”

    Who is this ‘we’ ? I see data being discussed here. Not anecdotes.

    Mr. Bennett continues:

    “Much of what we are learning has no meaningful context.We don’t know precisely what causes it; we don’t know if it is short or long term; we don’t know if the eventual effect will be positive of negative with regard to global temps.”

    What is this ‘it’ ? Perhaps Mr. Bennett would care to give an example ?

    Perhaps he might comment on the putative lack of context in the paper we are discussing ?

    Or, perhaps, (be still, my beating heart) he might leave us alone to learn some science in peace?

    Now, as to the subject at hand: Would it be true to say that there is no impact from black carbon on Antarctic ice ?

    Comment by sidd — 22 Apr 2009 @ 4:27 PM

  38. SecularAnimist (#31), I’ll trust current climate models to give us the general outlines you mention, like inundated coastlines and melting permafrost. (So I’ll pass on that beachfront property on the Maldives.) But should I trust them

    to help businesses, elected officials and regulators make good decisions on issues like where to put buildings or roads or wind farms

    as Lubchenco put it in the quote at #24? Are forecasts of regional and local impacts of climate change already so meaningful and reliable that climate models can serve as local area planning tools? If not, I’d worry about the impact of such claims on public confidence in the science.

    (recaptcha: “new drill” — how did the oil industry slip that one in?)

    Comment by CM — 22 Apr 2009 @ 4:36 PM

  39. Some folks are saying that the problem of uncritical acceptance of convenient data cuts both ways. And it’s true that you can find individuals on all sides making strong claims with weak foundations, and naive over-confidence.

    This not even close to being an equivalence of two sides on AGW.

    The place to go for forthright acknowledgement of genuine problems and uncertainties, wherever they lead, is the mainstream of science, and the IPCC reports which are based upon that mainstream. Drew’s paper is a case in point. Lots of people have fallen over themselves in haste to present Drew’s work as a useful correction to an improper scientific fixation on greenhouse warming. The truth is that Shindell and Faluvegi build on and extend a large body of work of aerosols which is straight out of the mainstream, developed by scientists who recognize the discovery of the anthropogenic greenhouse impact.

    The importance of greenhouse warming is basic physics, and the narrow confidence bounds for greenhouse forcing in IPCC 4AR are a true reflection of how solid this is as science. Using acknowledged areas of real uncertainty (aerosols, clouds, sensitivity, regional patterns of change, etc, etc) as a reason to be dubious of everything else about climate science is a fallacy. It arises because there is a strong desire to deny the anthropogenic emissions link; to the point where AGW-denial is riddled top to bottom with dubious hypotheticals, credulous acceptance of convenient speculations, and a strong thread of outright pseudoscience.

    This doesn’t mean everyone questioning AGW is a pseudoscientist. Many people are genuinely confused and simply don’t know who to trust.

    Walt (#34) is quite right that everyone involved needs to be careful about over reaching and stretching information. My point is that this caution is not needed for the great majority of scientists working away at the issues, but it is needed for nearly all of the “skeptics”.

    This is not a case of scientists needing to learn from the skeptics. It’s almost entirely the other way around.

    Comment by Duae Quartunciae — 22 Apr 2009 @ 4:59 PM

  40. Walt, I do not feel the necessity to hijack this good thread with another “warmist vs. denialist” back and forth.

    AGW is not even a theory in the sense that you think it is. There’s also better things to talk about then if AGW is “right or wrong” which by itself is essentially meaningless. This isn’t the binary black and white world you think it is.

    Gavin, I do have another question concerning Koch et al (2009) on aerosols, of which you were a co-author. I was wondering if you can briefly elaborate on the physical mechanism whereby aerosols can still have a cooling effect during the cold season at high latitudes when there is little to no incident sunlight. The paper talks about a delayed effect, but how exactly does this work?

    Comment by Chris Colose — 22 Apr 2009 @ 5:24 PM

  41. While I appreciate the opportunity to engage folks here on this AGW site, IMO some of you are misunderstanding some key points and making it difficult to have honest simple conversations.
    Let’s try and communicate.
    Making things up or wild embellishments without any basis are happening as I listed some above.

    Some of your responses were not right.

    There is nothing in the IPCC reports, or other science that established a threat that Hartman claimed, “if we don’t act fast on AGW the earth will become uninhabitable for humans and all other living creatures”.
    That is reckless embellishment at best. Making things up IMO.

    None of the various sea rise-100 million climate refugee etc. scenarios spell out what Hartman made up.

    His MWP message is stale and wrong too.
    The MWP has been firmly established as a global warming, according to data published by 695 individual scientists from 405 separate research institutions in 40 different countries. This does cause severe problems with the hockey stick theory and by extension AGW.
    Especailly when considered along with many other problems.

    Steven Chu is making up his hurricane warning. Talk show host Nancy Skinner embellishes the falsehood with “more category 5 hurricanes will be hitting the USA.
    IPCC assessments in 1995 and 2001 concluded that there was no global warming signal found in the hurricane record.

    Yet it’s still a regular claim that Hurricane Katrina was caused by AGW.

    OSU professor Jane Lubchenco made up her claim that ocean dead zones were linked to AGW. That was accepted without ANY science and distributed around the globe. Google it and look at how far it flew.

    Even though Lubchenco’s her own research group “cautioned that it is unclear what — if any — link the dead zone has to climate change”.
    Yet Lubchenco made her report that made the link.

    Now that’s making things up. It’s wrong.

    This is no joke.
    The claims do grow wilder and yet somehow more certain.
    Mark views all of this as facts?

    SecularAnimist went wild right here claiming climate models locate future water shortages, permafrost melt and flooding etc.

    Now I am certain many of you know climate models do no such thing.

    They certainly DO NOT forecast wind patterns 100 years out as Lubchenco made up.
    Talk about a whopper. That’s as bad as her ocean dead zone tale.
    More “facts” Mark?
    Secular wandered with supposed massive anthropogenic global extinctions.
    He says it’s not hard to “envision”
    This is a science blog and he’s fantasizing. Making things up.
    And you wonder why skeptics are skeptics?
    But he’s also stuck on Wikipedia where the MWP is still misrepresented.
    And he has bought the hurricanes lie and calls it “mainstream climate science.”

    What a perfect demonstration of made up science being circulated morphed into “mainstream climate science”.
    Even when it contradicts the IPCC reports.
    IPCC assessments in 1995 and 2001 concluded that there was no global warming signal found in the hurricane record

    Are those “adjectives and attitude” and not “substance”?

    There’s nothing wrong with my skepticism, attitude or approach.

    ccpo is concerned that skeptics lie. That they focus narrowly or something.
    Anyone following the work of skeptics scientists could hardly call it limited or narrowly focused.

    ccpo says they “never deal with Arctic sea ice”?

    Huh? Well that’s ccpo making things up.
    How can it not be known that Arctic sea ice is a regular, well monitored topic of research and discussion?
    And that it’s about to reach the 1979-2002 average.
    Antarctic sea ice is more stable and as a continent is growing.

    Yet while all of these uncertainties, misunderstanding and fabrications flourish the alarms get louder by AGW proponents.
    scared and are far more pessimistic than their public pronouncements indicate.

    In the mean time why can’t we have honest conversations?

    Comment by John H. — 22 Apr 2009 @ 5:30 PM

  42. Regarding Walt’s #34 post, why not just stick with what apparently is done at Duae’s physicsforum by sticking with peer-reviewed material? Out go the anecdotes, right?

    But wait! Brief scrutiny of RC reveals that with the exception of book reviews and some general commentary it seems the RC principles already bases most topic threads on peer-reviewed material. Most if not all anecdotal input is dragged in from external sources, often of poor fabric and much the worse for wear.

    Walt’s suggestions that we find a common dialog and learn to understand differing points of view is admirable but at the same time some parameters on that idea need to be established.

    For instance, I can’t support a discussion on geochronology if I’m speaking with a person who believes the world is 6,000 years old; I simply don’t believe in magic, unsupported as magic is in the peer-reviewed literature. Just so, I can’t have a useful discussion with somebody who sincerely believes they’re struggling against a global conspiracy of scientists bent on unhinging civilization, a fantasy beyond magical thinking and into the realm of sad pathology.

    Equally, I can’t bring myself to have a serious discussion with somebody incapable of stringing enough thoughts together to understand the chain of causation that physics tells us will happen when we unleash a relatively sudden flood of a relatively large amount of CO2 into the atmosphere. Can I succeed in explaining long division to somebody unable to fathom multiplication?

    Somebody without a sufficient grasp of well-established science is not going to be able to have a rough understanding of why a competently assembled computational model of Earth’s atmosphere can deliver useful results. I personally think that’s why so many “skeptics” are so strangely suspicious of the concept and utility of simulations.

    So by all means, understanding where understanding is possible is a good thing. All the same, let’s also remember that contorted equivocation is pointless and counterproductive.

    Comment by Doug Bostrom — 22 Apr 2009 @ 5:43 PM

  43. Question for Dr. Shindell or those familiar with his work: How does your recent study differ significantly from recent work by Ramanathan & Carmichael? Does it mainly present details on regional effects?

    Comment by MarkB — 22 Apr 2009 @ 6:20 PM

  44. He’s Baa-aak. I hope this thread doesn’t degenerate into all kinds of OT arguments about the sincerity of one side or the other. The Shindell-Faluvegi paper is a lot more interesting on the effects of aerosols wrt AGW, the different impacts in different latitudes,the results of less sulfate emissions in western nations, etc,than whether a protagonist or antagonist is sincere or not. As Duae states in an earlier post, their work indicates a way to reduce uncertainty of the effect of aerosols, not the uncertainty of and any given individual’s position
    on climate change.

    Comment by Lawrence Brown — 22 Apr 2009 @ 6:37 PM

  45. Re: #39


    AGW is in fact a theory, that human activity, specifically land use changes and greenhouse gas emissions, will warm the planet. It is an adjunct to GW theory itself, which states that greenhouse gases are what allow planet Earth to maintain a constant temperature which is 33K above what it would otherwise be.

    And to those who think this is a public policy nuance, you will need to reconsider that misguided notion.

    This is the heart of the matter.

    There is no question in most of our minds that AGW Theory is basically correct: short term climate sensitivity to a doubling of CO2 is 3*C+/-1.5*C. There is strong geological evidence that such an increase will cause significant sea level rise.

    Stop there.

    Every other “theory” (hypothesis, model result and so forth) is a guess. It is likely a highly educated guess, but who can say: in the year 2100 will there be more or less livable land mass than there is today? Will there be more or less food? Easier or more difficult shipping and transport? Will humans do poorly or maybe will they be better off?

    That’s where the doomsday scenarios come in. More desert, more storms, more severe storms, and on and on and on, mass extinction and on and on and on.

    That was the original commenter’s point, and I don’t know why it’s so hard to see, I honestly don’t.

    I have news for you: we’re all going to find out. In 2100 we will no longer be burning fossil fuels at anywhere near today’s levels, but by then atmospheric CO2 will be 500 or higher, because even after we stop contributing to the rise, the oceans will, the permafrost will, the lake beds will and so forth. It is as inevitable as it is inexorable.

    So we will see sea level rise, for sure, and some of today’s low lying lands will become bad places to live, and there will be mass migrations and certainly heavy loss of life. Again, I say: inevitable. What will emerge from that period?

    For all we know, a more vibrant planet and a more compatible and sustainable human footprint. Perhaps man and all other life will simply find a way to adapt to a planet where average seasonal temperatures are a few degrees higher than they are today.

    In any case, nobody knows, and the skeptics know who the fool is in that equation.

    Comment by Walt Bennett — 22 Apr 2009 @ 7:22 PM

  46. #34 # Walt Bennett

    You continue to say things that are contextually irrelevant, even though you think they are relevant.

    We simply ‘know’ scientifically (with reasonable certainty based on relevant contexts), a lot more than you ‘believe’.

    And just because you think we don’t know those things reasonably well, or reasonably well enough to gauge their meaning in the context of future warming and climatic impacts on the human population and global economy, does not change the well reasoned science and the resultant well reasoned knowledge and understanding.

    You really don’t seem to have a good idea of the contexts involved from a scientific point of view.

    Yet you keep writing about how important your perspective is? Even though you have contradicted yourself many times as I, and others, have previously pointed out.

    This is kinda weird, don’t you think?

    Or do you think it is important to keep things as confused as possible to avoid needed action, due to your own perceptions? And if so, what is your motive, because it is obviously not based in the well understood science?

    You state:

    Much of what we are learning has no meaningful context. We don’t know precisely what causes it; we don’t know if it is short or long term; we don’t know if the eventual effect will be positive of negative with regard to global temps. What about any of that would make a skeptic stop being skeptical?

    1. Additional GHG’s impose additional forcing in the climate system
    2. The atmospheric lifetime of CO2 is hundreds of years.
    3. The paleo record combined with the quantitative analysis of addition GHG’s and reasonably expected feedbacks will produce positive forcing. The Magic cloud albedo of Richard Lindzen has no support in the paleo record (are you willing to state, and substantiate, it has not been warmer, or even much warmer than the current GMT?).

    How is it that you keep missing the science? Is your opinion getting in the way? It’s almost seems that your brain is stuck in the wrong gear?

    Lastly, IT’S NOT ABOUT EACH OTHERS POINT OF VIEW. It’s about the well understood science and the evidence modeled and measured.

    I also agree with Chris Colose, let’s not cloud this thread with such opinions, and he put it well, “warmist v. denialist” though I would add “v. science”.

    Comment by John P. Reisman (OSS Foundation) — 22 Apr 2009 @ 7:24 PM

  47. Walt #44: “Perhaps man and all other life will simply find a way to adapt to a planet where average seasonal temperatures are a few degrees higher than they are today.”

    Really, really quickly, right? And “all other life” lacking as it mostly does any notion of the future will have to adapt even faster.

    Right, sure, somehow all this adaptation will happen very, very quickly, with few or no casualties. There’s wild conjecture, all right.

    Here we are, once again, back at the pre-Enlightenment level and resorting to fantasizing a magical world where poor dumb beasts suddenly develop astounding powers of adaptation.

    As other posters have begged, can’t we move ahead from this incredibly infantile sort of conjecture? Why is that every single thread on this sight is quickly dragged down to the “EZ Science for Unicellular Organisms” level?

    I’m done with this sort of “discussion”. The science is in good hands, I’m sure of that, but the public understanding is stuck at about 6 years of age wth no improvement apparently possible.

    Comment by Doug Bostrom — 22 Apr 2009 @ 11:44 PM

  48. Perhaps the moderators might consider a more stringent policy, based on relevance to the topic at hand.

    I come to this site to learn science. Yet I see the same old lies propagated in comments every day. I am sorry if I feed the trolls, but I sometimes feel compelled to respond. Hopefully, the more receptive will actually read these references.

    re: ocean dead zones:

    “Long-term ocean oxygen depletion in response to carbon dioxide emissions from fossil fuels’. Nature Geoscience, (in press)”

    re: wind patterns, Hadley cell expansion and increasing aridity:

    re: increased hurricane incidence and quotes from IPCC 2001 and previous: science has not stopped since 2001:

    re: MWP : dear god, not this again. MWP was not global, discussion on this site at

    Each of these references is easy to find, together with many more. Sometimes I feel that I am trapped doing homework for a horde of lazy children.

    Now a question on the lasting effects of black carbon. If we have a layer of black carbon on the surface of an ice sheet, how long would it last in the absence of further deposition. Let us say that we could stop depostion of black carbon on the Arctic ice sheets today. How long before the already deposited carbon is carried away by meltwater and albedo returns to normal ?

    Comment by sidd — 22 Apr 2009 @ 11:49 PM

  49. Re: #44 Walt Bennett

    Having just endured three days of summer temperatures in April, I’m not anxious to feel the effects of warming in coming years.

    On Monday, California broke temperatures records from the Oregon border to the Mexican border — sometimes by as much as 12 degrees F. Yesterday, more records were broken (but only by 11 degrees F). Today, it was only from Medford, Oregon to Fresno — only half the state.

    Yes, this is weather, not climate. But in my 60 years in California, I have never seen any spring event that shattered such high temperature records statewide. Maybe it’s time to start thinking that we really are seeing signs of warming now, not just debating a theoretical warming in the future.

    Comment by Jim Eaton — 23 Apr 2009 @ 1:04 AM

  50. #40 John H

    While I don’t think that all creatures will die, likely a tremendous number of species are at risk and will die if we don’t act rather fast. Many species extinctions may now be inevitable based on current human effects, impacts, and that includes global warming.

    How does MWP hurt the hockey stick? Here is the hockey stick with the MWP which is included in IPCC reports toward the bottom of the page:

    It is reasonable that global warming will produce more cat 5 hurricanes. What is it about ‘warmer water gives more energy to hurricanes’ that you don’t understand.

    There is a lot going on in the oceans, maybe you should take a look at the ocean studies to understand the different human impacts on the earth oceans

    As to water shortages well, Hoover dam is expected to shut down in 2023 according to the folks at the dam due to all the water disappearing and there is a clear latitudinal shift pushing water north, which will cause in more southern regions… uh, what do you call it??? oh yeah, water shortages.

    As far as envisioning goes, it is not unreasonable to envision the changes and their effects (and the increasing costs). Same for you take on IPCC reports of hurricane signal. There is a visible trend already, so I guess you are one of those that believe we should wait until it’s worse, but you don’t understand the forcing and the inertia issues not to mention the feedbacks.

    Generally speaking you are a unreasonable on these issues.

    Arctic Sea ice mass is rapidly diminishing and the Antarctic WAIS is not stable, and while there is more snow falling down there increasing mass that actually confirms global warming and has been expected in the models.

    Generally, it’s a really good idea to study to understand the relevant contexts before you post such out of context stuff.

    As far as honest conversations, let’s be honest. Things are not exactly rosy in our environment, species reduction and extinction is a huge issue and it’s going to get worse… our best chance is to work hard and fast on solutions.

    Comment by John P. Reisman (OSS Foundation) — 23 Apr 2009 @ 2:09 AM

  51. Walt, there’ll be less land. There’ll be less food (unless we go back to eating tree roots). We’ll be worse off.

    Otherwise, prove there’ll be more land. Prove that there’ll be more food.

    The Oracle Says: naughty cap

    I suggest you wear it.

    Comment by Mark — 23 Apr 2009 @ 2:37 AM

  52. “Many people are genuinely confused and simply don’t know who to trust.”

    Yet somehow they trust the people who make trillions off the status quo when they say that the status quo is fine as much as the people who make a wage off their research when they say their research is correct.

    This is willful confusion, if it is confusion at all.

    Comment by Mark — 23 Apr 2009 @ 2:41 AM

  53. Is it possible to just throw away John H and Walt Bennett from this thread? There are ample places their can present their BS. We had a nice scientific discussion about to start until John H came with his hackneyed agenda. You do not need to kill them, just move these comments to the end of some other discussion, which have already degenerated.

    Comment by Petro — 23 Apr 2009 @ 3:50 AM

  54. Walt Bennett writes:

    We have to find a common dialog and learn to understand each others’ point of view. Most of you in here have NO INTEREST AT ALL in that.

    That’s because we don’t think w DO have to “find a common dialog and learn to understand each others’ point of view.” I understand the denier point of view perfectly well, but I have no desire or interest in trying to dialog with them. Why should I? Their minds are made up. I’m interested in talking to people who are on the fence, or who are trying to learn, but trying to find a “common dialog” with pseudoscience crackpots is a waste of time. What “common dialog” can there be with someone who thinks the greenhouse effect violates the second law of thermodynamics, or that global warming is caused by the sun? Should I look for common dialog and understanding with people who reject relativity or think Apollo 11 never landed on the Moon? Why?

    Comment by Barton Paul Levenson — 23 Apr 2009 @ 6:51 AM

  55. John H. writes:

    There is nothing in the IPCC reports, or other science that established a threat that Hartman claimed, “if we don’t act fast on AGW the earth will become uninhabitable for humans and all other living creatures”.

    I guess it depends on how you define “acting fast.” If we don’t act fast, AGW will get much worse, and if it gets bad enough, it could trip geophysical feedbacks which would amplify the problem to the point where we couldn’t solve it. If that happens, and the Earth’s mean global annual temperature is doomed to rise 6 K or more, then it may indeed become uninhabitable for humans. At +6 K ocean chemical changes may lead it to bleed out hydrogen sulfide, and if that happens we’re all dead.

    That is reckless embellishment at best. Making things up IMO.

    See above.

    None of the various sea rise-100 million climate refugee etc. scenarios spell out what Hartman made up.

    If half of Florida and all of Bangladesh are under water a hundred years from now, then there will be AT LEAST 100 million climate refugees. That’s not made up either.

    His MWP message is stale and wrong too.
    The MWP has been firmly established as a global warming, according to data published by 695 individual scientists from 405 separate research institutions in 40 different countries.

    Care to cite a source, preferable from a peer-reviewed science journal? Your list is impressive but lacks any specifics. As I understand the MWP was NOT global and was certainly not warmer than today.

    This does cause severe problems with the hockey stick theory

    It might if it were true, but it isn’t.

    and by extension AGW.

    Except that AGW doesn’t depend on the “hockey stick,” whatever you’ve read in climate denier blogs.

    Comment by Barton Paul Levenson — 23 Apr 2009 @ 6:58 AM

  56. ***# John H. Says:
    22 April 2009 at 5:30 PM

    In the mean time why can’t we have honest conversations?***

    To be honest, I don’t think there are any honest skeptics, professional or not. I must explain, however, my concept of honesty. I’m not a fan of the PC speak, nor of extreme complexity. Simpler is often better. So, wrt climate denialists I don’t care about the **degree** of the lie, only that it exists. Why? Because we know too much about the sources of the lies, disinformation, etc. We know it was largely the result of the Marshall Institute and Exxon. These are facts. Virtually all of the “skepticism” exists because of these two organizations, whose sole goal, also fully documented, has been to not even prove the science wrong, but to simply sow doubt to slow down and/or prevent action to protect political and/or financial interests.

    Thus, all this “doubt” is manufactured. There is no room for consequential doubt in the science. To wit:

    Virtually all of the anti-AGW “science” is traceable to the two organizations and their many proxies. Given this, pretty much all “skeptic”-ism is a result of ideology or lies. (Self-delusion, btw, is just another kind of lie.) It truly is simple: all of you are either too tied to your ideology, too tied to your delusions, too tied to your fossil fuel-abetted incomes (oil touches everything, no?) or are plain old brainwashed.

    The proof is simple: How many studies are there supporting AGW? How many thousands? How many supporting anti-AGW? A handful? A couple handfuls?

    How many climate scientists support AGW? 97% according to the most recent poll.


    Simple fact. According to the link above wrt meeting the 2C target: “86% of the experts told the survey they did not think it would be achieved.”

    So, not only do they support the basic science, they are expecting disaster at a clip of 86% of those polled!

    But let’s let the science talk: Can you name me even five scientifically sound, peer reviewed papers that are unambiguously supportive of an anti-AGW stance?

    The only survey of science papers I know of done back in ’03 or ’04 found the ration of pro/anti at 1,000:1. I see zero evidence this has changed.

    There was another review done last year that found 90% of all anti-AGW books were linked to the network referenced above of political activism.

    Then, there are the global changes being seen. The trends, the changes, the extinctions. And, this is where the science starts, not what it falls back on when challenged. Or are you not aware of scientific method? Observe > hypothesize > test > record > analyze > conclude. It doesn’t start with “assume” nor does it start with “model.” It starts with observe. I literally have seen no comments, no papers, nothing, that started with a simple observation of the natural world from skeptics. They are all starting from the point of attempting to support the presupposition that AGW science is wrong.

    If there are any out there, do share.

    And what of the Arctic? If not AGW, then what? What of methane concentrations rising as we start finding evidence of increasing clathrate releases, permafrost thawing and thermokarst lakes?

    What of the global temps? What of the habitat changes? What of changes in rainfall amounts and patterns? What of the strength of cyclones/hurricanes? What of earlier springs? What of extreme weather events? What of models understating the speed, depth and breadth of changes? What of the scientists scared by what they see?

    The evidence is so vastly overwhelming in its totality that to claim it is weak and uncertain is ridiculous. You are conflating uncertainty in specifics with uncertainty in the overall weight of the evidence. In other words, you are lying. (You are free to choose the form of lie you wish to be labeled with, but know this: it is a lie of some sort.)

    ***There is nothing in the IPCC reports, or other science that established a threat that Hartman claimed, “if we don’t act fast on AGW the earth will become uninhabitable for humans and all other living creatures”.***

    That is a lie. The possibility of rapid climate change of 7+C in as little as a decade is known. The possibility of a world 6+ degrees warmer is well known. Both of these could so disrupt carrying capacity so as to knock humanity off the the face of the planet, and definitely would render our current civilization a ruin.

    If you find some use in trying to say the person should have made a distinction between all dying and virtually all dying and civilization being rent asunder, go ahead, but you’re playing games. (Another form of lie.)

    Re: hurricanes. You’re using findings based on science and measurements that are at best more than ten years old? This is just another form of lie.

    Dead zones: you have proof they aren’t?

    Do you really think there won’t be extinctions when there already are?

    I tire of your childish rhetoric. You are taking a simple fact of science and warping it into a huge lie: Uncertainty in facts and the inability to establish 100% causation = not possible, not happening.

    You are also holding all AGW-concerned people to the standard of science. This is a science blog, but not all posters are scientists. It’s the same stupidity visited on AGW activists about Gore. Gore said! 1. Who cares what Gore said about climate science? He’s not a scientist. 2. He can say anything he wants as a private citizen.

    I, as a non-scientist, am free to suppose, to guess, to assume, to extrapolate without having to prove anything at all. In fact, if I fully believe a danger exists, I am ethically and morally bound to speak out. The caveat being I must be truthful.

    E.g., after IPCC 4 came out, I, non-scientist, immediately concluded A. ice melt was much higher than stated, B. Arctic melt and Antarctic melt was higher than stated, C. that SLR was accelerating and that AGW in general was moving much, much faster than stated.

    How was I able to do this? Simple: real world observations and IPCC4 didn’t match up.

    But, you see, I CAN do this because I am not bound by the same constraints as scientists. For you to pretend, in order to support your agenda of do-nothing, that I and all other activists are constrained by scientific rules and 100% certainty is a gross distortion of reality. It is nothing more than a tactic aimed at slowing reaction to AGW. That is, it’s a lie.

    ***There’s nothing wrong with my skepticism, attitude or approach.***

    Oh, there very much is. See above.

    ***Anyone following the work of skeptics scientists could hardly call it limited or narrowly focused.***

    Because you assert it? First, they produce practically no science of their own. Why? (Rhetorical.) There is nothing for them to produce. They prefer to spend their time, like W. Soon, pretending to debunk the actual science being done.

    Show us the vast work of anti-AGW science. Please, set up a web page that lists the vast array of this science, then another with the AGW-supporting science. I dare you.

    ***ccpo says they “never deal with Arctic sea ice”?

    Huh? Well that’s ccpo making things up.
    How can it not be known that Arctic sea ice is a regular, well monitored topic of research and discussion?***

    By skeptics? Show me their research.

    And that it’s about to reach the 1979-2002 average.

    Now that’s just another huge lie. It’s not terribly important for record keeping what the ice does on the up or down slope. You are pulling the same slight of hand G. Will pulled a few months back. Did it get anywhere near the average at its highest extent? No. The peak of extent was one of the lowest in the record.

    Why lie by omission?

    Antarctic sea ice is more stable and as a continent is growing.

    And, if true, is one of the least relevant metrics you could consider. Why do you emphasize that, emphasize the extent of Arctic ice at a non-peak period, but not mention at all that Arctic ice **mass** is down 80%? Or that the lowest 5 extents have all been in the last five years? Or that old ice is down to around 30%? You know… issues that actually MATTER.

    I don’t find you an honest opponent. This is not a surprise, obviously.


    reCAPTCH: its epcot
    I.e., fantasy. How very true, eh, Mr. H.?

    Comment by ccpo — 23 Apr 2009 @ 7:38 AM

  57. Re: #53

    Bart (and by proxy all others who commented on my comment):

    I am not suggesting some sort of equalized discussion with deniers; I am saying that skepticism is real, necessary and more reality based than the views of many “warmers”.

    I am saying that the fool is the person who thinks he knows all he needs to know.

    Mark: there will likely be less total land in 2100; I asked, will there be more or less LIVABLE land? You don’t know and you can’t know.

    That’s the sort of skepticism I am referring to. Nothing “infantile” about it. I fully accept that we are warming and will continue to warm and that there will be significant change resulting from that.

    And I hardly think a comment here and a comment there warrant any sort of “take away his keyboard!” response. What are you so afraid of?

    Anyway, we can have a nice robust discussion about this at

    I welcome all views.

    Comment by Walt Bennett — 23 Apr 2009 @ 8:35 AM

  58. ref #55 “Dead zones: you have proof they aren’t?”

    The dead zones, at least in the Gulf of Mexico, are not a particularily recent problem. I recall reading about these many years, possibly decades, ago as a result of the run off of fertilization occuring in the Mississippi basin. I see no reason to believe the fertilization has decreased and therefor no reason to believe the cause as understood then is not the cause now. Perhaps it has been disproven that this was actually the cause and I am unaware of it?

    Comment by steve — 23 Apr 2009 @ 8:37 AM

  59. Lots of bovine affluvium in this thread, which is typical. I’d bet more than half (three quarters?) of the comments and responses to comments are irrelevant to the topic introduced in the lead-in discussion.

    [Response: Indeed. We’re going to try and get back on topic and try and control the noise. So people who want to argue about policy can do it somewhere else. Comments are either on topic or deleted. – gavin]

    Comment by Rando — 23 Apr 2009 @ 9:05 AM

  60. Perhaps it has been disproven that this was actually the cause and I am unaware of it?

    Or perhaps the scientist in question, an oceanographer at Oregon State University before joining the Obama administration, was talking of the intermittent dead zones being studied off the *Oregon* coast, not the gulf.

    Changes in the timing of upwelling off the Oregon coast has been linked to global warming.

    Comment by dhogaza — 23 Apr 2009 @ 10:56 AM

  61. I would say they produce high ejecta mass eruptions of bovine effluvium. I would not say it is an aerosol, but it sure does have a sort of stench in the cloud of obfuscation they seem to be producing that could fog the unsuspecting readers vision.

    I am generally against censorship, but the relevance level needs to be higher. John H., Walt Bennett and Todd Bandrowsky seem to mostly distract and eat up valuable time and space with obtuse arguments (if they write with relevance it would be a different story). It’s Red Herring day every day with these guys. They, like others, may also be trying to get the banner of RC banned me so they can whine in the denialosphere? They distractions sort of remind me of Lomborg:

    and the ‘do you beat your wife (yes/no)’ poll

    Back to aerosols, I started an item on aerosols, relevant comments and criticisms welcome.

    Comment by John P. Reisman (OSS Foundation) — 23 Apr 2009 @ 11:02 AM

  62. Could someone comment on my earlier comment #23. It seems to me that this study holds out the possiblity that all or most of the total artic warming is due to black carbon – and not to CO2. I believe this is directly on topic and would appreciate some thoughts on my observation.

    Comment by RickA — 23 Apr 2009 @ 11:29 AM

  63. I do have a question, which is hopefully on topic.
    Discussing the effects of aerosols on warming and the decrease in temperature in the 1940’s.
    I have been wondering if the World War had any (maybee very small) part in this. Could the dust and chemicals have any measurable effect on regional or global climate for probably just a short period?

    Comment by MS — 23 Apr 2009 @ 2:15 PM

  64. My link has been wrong; it was missing the “s” in “blogspot” and directed to a religious site.

    The link should work now:

    Comment by Walt Bennett — 23 Apr 2009 @ 3:14 PM

  65. This is sad. The contribution by Drew is very interesting. Check out the subtle interplay between the large increases in black carbon from Asia and the reduction in sulfate emissions and the effects in mid latitudes of the northern hemisphere and the arctic, yet we’ve been bombarded with a lot of OT from the ususal suspects. WB hasn’t once mentioned aerosols in his numerous posts on this thread. Not one time!Is it possible to use his words, that he has NO INTEREST AT ALL in this topic. This post deserves better.

    Comment by Lawrence Brown — 23 Apr 2009 @ 3:45 PM

  66. “It seems to me that this study holds out the possiblity that all or most of the total artic warming is due to black carbon – and not to CO2.”

    So just because *some* of the warming *can* be attributed to black carbon, you decide that there’s a possibility that ALL or most of it is.


    Comment by Mark — 23 Apr 2009 @ 4:23 PM

  67. Like all of the climate models, there is a huge temperature range here, that may, or may not, be attributed to the elements being modelled.
    Once again, the debate is based around the models and the question, again, is “How reliable are the models in predicting the future”?
    Taking the GISS Model E predictions as of 2003, current global mean temperatures are .15C below those predicted by the model.
    The models are not proving to be very good at prediction, they may be “tweakable” to give a reasonable representation of the past, but that isn’t of much use to us if they can’t predict the future with a reasonable degree of accuracy.
    This quote gives me problems.
    ” During the last 3 decades (1976-2007), the best fit to the temperature responses in the models require negative forcing from tropical aerosols but positive forcing from Northern Hemisphere mid-latitude aerosols”
    So we have both +ve & -ve forcings needed to get the models to fit the measured temperatures and the same aerosols are supposed to do this?

    Comment by Adam Gallon — 23 Apr 2009 @ 4:33 PM

  68. Response to RickA at #62. Yes, the paper is saying that the immediate cause of most of the Arctic warming is the impact of aerosols and black carbon.

    From the paper: (page 298) ” During 1976-2007, we estimate that aerosols contributed 1:09 +/- 0:81 C to the observed Arctic surface temperature increase of 1:48 +/- 0:28 C.”

    The paper looks at regional response to greenhouse, and CO2 in particular, on page 296; and concludes that the regional response to CO2 is similar to the response for other forcings. That’s not a comment on total magnitude, but on whether there is any localized amplification of the global CO2 effect. There isn’t… and that implies the CO2 impact should be about the same in the Arctic as anywhere else.

    The Arctic is warming much more rapidly than the global mean, according to the paper, because of a local aerosol and black carbon effect that is locally larger than the underlying global greenhouse driven trend.

    Disclaimer. I’m not a climatologist… I’m just reading the paper as best I can.

    Comment by Duae Quartunciae — 23 Apr 2009 @ 4:58 PM

  69. RickA (62) — I think
    Accuweather Climate Blog
    or else maybe
    has a recent thread about an attribution study regarding black carbon in the Arctic. Both sites are linked on the sidebar.

    Comment by David B. Benson — 23 Apr 2009 @ 5:20 PM

  70. ref #60 dhogaza thank you, apparently I was off topic from even the off topic topic

    Comment by steve — 23 Apr 2009 @ 5:42 PM

  71. The temporary dip in temperatures around the middle of the 20th century was substantially(?) caused by aerosols. What is the current aerosol release compared to back then? Is this period a second aerosol dip – though a degree F warmer? If one counts the late 19th century, this could even be the third dip. If so, interestingly enough they are all approximately 50 years apart and 1F higher each time.

    Comment by RichardC — 23 Apr 2009 @ 7:23 PM

  72. From the IPCC FAR, Chpt 2:

    Aerosol effects on radiative forcing are divided into four categories:

    1) direct effect – “the mechanism by which aerosols scatter and absorb shortwave and longwave radiation, thereby altering the radiative balance of the Earth-atmosphere system.”

    2) cloud albedo effect – “the microphysically induced effect on the cloud droplet number concentration and hence the cloud droplet size, with the liquid water content held fixed.”

    3) cloud lifetime effect – “the microphysically induced effect on the liquid water content, cloud height, and lifetime of clouds.”

    4) semi-direct effect – “the mechanism by which absorption of shortwave radiation by tropospheric aerosols leads to heating of the troposphere that in turn changes the relative humidity and the stability of the troposphere and thereby influences cloud formation and lifetime.“

    Two other definitions to keep in mind:

    Radiative forcing: “the change in net (down minus up) irradiance (solar plus longwave; in W m–2) at the tropopause after allowing for stratospheric temperatures to adjust to radiative equilibrium, but with surface and tropospheric temperatures and state held fixed at the unperturbed values.”

    Surface forcing: “the instantaneous perturbation of the surface radiative balance by a forcing agent. Surface forcing has quite different properties than RF and should not be used to compare forcing agents (see Section 2.8.1). Nevertheless, it is a useful diagnostic, particularly for aerosols.”

    Here is the relevant section 2.8.1 quote:

    For example, for absorbing aerosol, the surface forcings are arguably a more useful measure of the climate response (particularly for the hydrological cycle) than the RF (Ramanathan et al., 2001a; Menon et al., 2002b). It should be noted that a perturbation to the surface energy budget involves sensible and latent heat fluxes besides solar and longwave irradiance; therefore, it can quantitatively be very different from the RF, which is calculated at the tropopause, and thus is not representative of the energy balance perturbation to the surface-troposphere (climate) system.

    Incidentally, here is a quote from the FAR on the split between fossil fuel and biomass as sources of black carbon aerosols:

    “Carbonaceous aerosol emission inventories suggest that approximately 34 to 38% of emissions come from biomass burning sources and the remainder from fossil fuel burning sources.”

    Finally, this was the conclusion of the Fourth IPCC report on the level of knowledge as of five years ago or so:

    “The increase in the knowledge of the aerosol-cloud interactions and the reduction in the spread of the cloud albedo RF since the TAR result in an elevation of the level of scientific understanding to low.”

    Considering that much of the influence seems to come from the indirect and semi-direct aerosol effects, does this study mean that “low” gets switched to “medium”, possibly even to “medium-high”? :)

    P.S. This comment immediately brings to mind the “cool phase of the PDO”

    “nearly all CMIP3 models require strong aerosol cooling at Northern Hemisphere mid-latitudes during the 1931-1975 period to capture both the global mean trends and the NH mid-latitude versus Southern Hemisphere extratropics temperature trends”

    The “cool phase of the PDO” is from 1945-1980, roughly… it’s looking more and more like the existence of predictable multidecade oscillations in the oceans is a myth – there are certainly fluctuations, but there is no reason to assume that future ‘cycle’ strength and timing would be any more predictable than El Nino is – assuming that the ocean-based ‘multidecadal cycle’ notion has any validity at all.

    Interestingly enough, the NAO index also seems to have that curious superimposed cool period on top of the short-term fluctuation, 1935-1980 or so… but that’s the AMO… which also has a similar “cool period”. According to the API/George C. Marshall crowd, we are about to plunge into another ‘cooling ocean cycle’ – and the last time they said that was in the 1990s and it was a ‘cooling solar cycle’ that we were about to enter. Curiouser and curiouser…

    Comment by Ike Solem — 23 Apr 2009 @ 8:49 PM

  73. Aerosols are an interesting topic but I am unclear on what value is derived from trying to model aerosols to explain decadal oscillations in global temperatures.

    I say that because oscillations likely predate much of this. Below is a link to fish scale deposits. These fishes are very abundant in the eastern pacific and one tends to dominate in rough relationship to ocean SSTs and have done for some time.

    There may well be some anthropogenic signals in the climate record but to ignore natural ones risks far overstating the anthropogenic effects.

    Interestingly, on the flip side of this anthropogenic activities (fishing) has long been fingered for declines in sardine abundances.

    Somebody somewhere has to be laughing at us!

    Seems to be some kind of an infectious disease. Perhaps somebody can work on a cure for that problem.

    Comment by Bill Hunter — 23 Apr 2009 @ 10:42 PM

  74. MS — yes, World War II had an effect in that the global economy went into high gear coming out of the Depression. Industrial production picked up massively in order to turn out weapons, and there was very little in the way of pollution control. One result was regional pollution disasters such as Donora, PA (1948) and London (1952).

    Comment by Barton Paul Levenson — 24 Apr 2009 @ 3:54 AM

  75. RickA (#62): it was noted in the post that

    As the total observed Arctic warming during 1976-2007 was 1.5 +/- 0.3ºC, our results can be portrayed in many ways: there is about a 95% chance that aerosols contributed at least 15% to net Arctic warming over the past 3 decades, there is a 50% chance that they contributed about 70% or more, etc.

    Perhaps someone numerate following this thread will work out the corresponding probabilities of 80%, 90%, etc. of the net Arctic warming being due to aerosols.

    But be careful drawing conclusions about the role of CO2.

    The paper infers the aerosol forcing from the difference between observed warming and the warming that can be accounted for by other forcings modeled, with uncertainties that are dominated by natural variability. The positive CO2 forcing is already in there before they work out the aerosol influence.

    So if you want the whole observed Arctic warming since 1976 to be due to black carbon, I guess you have to posit natural variations cooling the Arctic enough to cancel out the warming due to CO2 and other GHG, natural, and ozone forcings.

    It would still be the case that CO2 is warming the Arctic. That is, given the same natural cooling and the same aerosol warming, the Arctic would not warm as much in the absence of increased CO2. See the dam analogy in the post.

    Correct me if I’m missing something, folks, I’m here to learn…

    Comment by CM — 24 Apr 2009 @ 5:41 AM

  76. Thank you for the clear post- some much needed context. The dam analogy was particularly helpful.

    Re #59 and Gavin’s response:
    I’d like to propose a reason for the high levels of ‘bovine effluvium’ and constant seepage of policy discussion into these threads. Until it is addressed the problem is likely to continue, regardless of how much RC authors insist this is a ‘science only’ discussion blog. Namely that ‘we’ (ie nonscientists/lay people) desperately want to know what climate scientists’ opinions are on proposed climate change policies, and it’s very hard to find these opinions elsewhere on the web. So we trawl the blogs where climate scientists occasionally break cover, trying to glean some idea of their thinking.

    I can understand why Gavin and others are keen to maintain the distinction between their work as scientists and their private views on policy, but as the science becomes more ‘settled’ these policy discussions are going to get more and more important. Most people accept the reality of AGW now, and the focus is shifting to how much, over how long, what we should be doing about it and how urgently. On the last two points particularly, there is a huge amount of uninformed opinion cluttering up the internet. It would be nice to see more informed opinion on the issue- if not on this blog than elsewhere. (And whose opinions could be more informed than those of working climate scientists?)

    Comment by Matt — 24 Apr 2009 @ 8:03 AM

  77. Re#76 If AGW was incorrect science would have demonstrated it for Science is set up to shoot itself down. Thats how as I understand science works. Peer review and scrutiny thereafter before anything is written into the annals of knowledge. Thats the issue with the skeptics, they attack everything in desperation but submit nothing for the scientific process to do its job.

    450 ppmv of CO2 is almost certain. Antarctica started to form then so WAIS is a definite issues of being severely eroded along with Greenland in the Arctic as it formed when Co2 was less than todays level hence it unease. The Arctic sea ice will continue on its increased summer melt (area and thickness) and will recover in the winter to but maybe even that is under threat.

    Lets hope that aerosoles have a small sensitivity whcih means that GHGs will have less effect as warming already expereinced will be due to more GHG required for its temperature rise. If Aerosoles have a higher -ve sensitivity effect then if we eliminate them then GHG will mean a stronger warming.

    Comment by pete best — 24 Apr 2009 @ 9:46 AM

  78. re #76.

    I agree. I am currently finding what I’m looking for at

    Comment by Douglas Wise — 24 Apr 2009 @ 9:58 AM

  79. I regret that I have been “suckered” into responding to off-topic comments by denialists with replies that were also off-topic.

    I appreciate with much gratitude that this site is about climate science, not climate/energy policy, renewable energy, nuclear energy, etc.

    Many of us who understand and accept what science has learned about AGW, while we continue to be interested in the ongoing development of scientific knowledge and understanding (the focus of this site), realize that science has already learned enough to know that the problem is real, the danger is grave, and the need for a policy response is urgent. And we naturally want to discuss those topics, particularly when an article on this site brings into sharp focus just how serious the problem of AGW is. But there are indeed other sites where discussion of political, economic and technological responses to the reality of anthropogenic global warming are more appropriate (e.g., and I will try to keep that in mind.

    Having said that, I think that the denialists are less likely than readers like myself to respect the moderators’ requests that comments stay on-topic. And if the denialists are permitted to post extended off-topic regurgitations of bogus, scripted, ExxonMobil-funded talking points, often with a tone of belligerent arrogance and derision towards those who accept the science, should those comments go unanswered?

    Comment by SecularAnimist — 24 Apr 2009 @ 11:28 AM

  80. #66 Mark
    As I said in my post #23:

    1.1 + or – .8 gives a range of .3 – 1.9 C for BC contribution
    1.5 + or – .3 gives a range of 1.2 – 1.8 C for total artic warming.

    What struck me about these two ranges is that the top end of the black carbon warming exceeds the top range of the total artic warming (i.e. 1.1 + .8 = 1.9, is larger than 1.5 + .3 = 1.8), so I infer from this that it is possible (maybe 5% possible – I don’t know how to calculate the exact probability) that all of the artic warming from 1976 to 2006 was due entirely to black carbon – and therefore none was due to C02.

    [Response: The two ranges are not independent. – gavin]

    I don’t know how much of the artic warming is due to black carbon – it is just interesting to me that it is statistically possible that all of the artic warming could be due to something entirely different than CO2.


    Comment by RickA — 24 Apr 2009 @ 1:01 PM

  81. #75 CM
    It is not that I want the entire artic warming to be due to black carbon. Rather, it is that if there is a possibility that the entire 1.5 +- .3 of artic warming is entirely due to black carbon; and given that the artic is supposed to be the most sensitive to global warming, then maybe we don’t really understand what is going on. Maybe we don’t really understand how CO2 impacts climate.

    Comment by RickA — 24 Apr 2009 @ 1:06 PM

  82. #80 – Gavin in line comment

    The two ranges are not independent.

    I assumed that the total artic warming was a measurement which measured total artic warming, from whatever source – whether it was CO2, black carbon, other cause, or some combination.

    Therefore, if the top end of warming attributable to just black carbon (1.9 C) exceeds the total warming observed in the artic (or more accurately there is some small probability that this is the case) – then all of the observed warming could be due to black carbon.

    Therefore, I do not assume they are independent, but in fact that the black carbon warming is a subset of total artic warming.

    [Response: You misunderstand. The conditional probability of BC provided 1.9C of warming given a total warming of 1.8C is zero. Generally, the joint pdf of the attribution and total warming will likely show a strong correlation between the two. – gavin]

    Comment by RickA — 24 Apr 2009 @ 1:22 PM

  83. Adam Gallon (87) — My understanding is that the ABC aerosols have both global cooling and regional warming effects; ain’t simple.

    RickA (81) — We certainly understand how CO2 impacts climate on centennial scales.

    Comment by David B. Benson — 24 Apr 2009 @ 1:39 PM

  84. RickA: I’d also encourage you to read the post more closely:

    “black carbon contributed 0.9 +/- 0.5ºC to 1890-2007 Arctic warming (which has been 1.9ºC total)” pretty clearly states BC’s contribution to Arctic warming in comparison to the 1.9 number, and it is clearly less than that number.

    Now, in the next sentence, “We also estimated that aerosols in total contributed 1.1 +/- 0.8ºC to the 1976-2007 Arctic warming. This latter aerosol contribution to Arctic warming results from both increasing BC and decreasing sulfate”: therefore, part of this is the warming from black carbon, but part of this comes from a _decreased cooling_ from sulfates.

    Note, also, that in a 3 decade period for a regional signal, there are a lot of influences. So, one might write an equality like:

    CO2 + BC + SO2 + internal variability + solar changes + … = observed change (+1.5 (+-0.3)). So if there are other influences in the Arctic that might have led to cooling in the past 3 decades, then there can still be warming from CO2 _even if_ aerosols explain “all the warming”.

    Comment by Marcus — 24 Apr 2009 @ 1:56 PM

  85. “Rather, it is that if there is a possibility that the entire 1.5 +- .3 of artic warming is entirely due to black carbon; ”

    Rick, how can it all be from black carbon?

    If there’s aerosols, CO2, H2O, clouds, ice albedo, Ucle Tom Cobblers and all, how can all the heating be from black carbon? Did the rest give up because black carbon was there??? Did he throw them out of the equation because he’s Big Black Carbon and he ain’t gonna share the artic with ANYTHING that will affect the climate…?

    If you boil a pan and pour in cold water so that the temperature doesn’t rise, then you rub the pan which friction causes the temperature to rise, is all the heating of the water in the pan on the stove because of you rubbing it???

    Comment by Mark — 24 Apr 2009 @ 4:50 PM

  86. Matt 24 April 2009 at 8:03 AM :

    Namely that ‘we’ (ie nonscientists/lay people) desperately want to know what climate scientists’ opinions are on proposed climate change policies, and it’s very hard to find these opinions elsewhere on the web. So we trawl the blogs where climate scientists occasionally break cover, trying to glean some idea of their thinking.

    But there are other global warming blogs which are much better for policy. For example,

    Comment by llewelly — 24 Apr 2009 @ 11:44 PM

  87. John H #41: what’s your source for your claim that

    The MWP has been firmly established as a global warming, according to data published by 695 individual scientists from 405 separate research institutions in 40 different countries.


    I found a web site making similar claims. I had a closer look at the data they were presenting and the dates don’t line up. Some spots were warmer 500 years ago, others 1,000 years ago, others 1,500 years ago.

    You can look at the temperature records at any randomly selected list of locations and you can be guaranteed that you will find some with unusually warm or cool periods that do not correspond to any worldwide trend.

    Take a look again at whatever source you thought was so credible and report back if you find something different. Better still, write a paper and get it published.

    Comment by Philip Machanick — 25 Apr 2009 @ 6:56 PM

  88. co2science is the source of that assertion. Caveat emptor, or, sourcewatch.

    Comment by Hank Roberts — 25 Apr 2009 @ 8:17 PM

  89. I did not see a reference to CCSP 2009. Maybe I missed it.

    CCSP 2009: Atmospheric Aerosol Properties and Climate Impacts, A Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. [Mian Chin, Ralph A. Kahn, and Stephen E. Schwartz (eds.)]. National Aeronautics and Space Administration, Washington, D.C., USA, 128 pp. (Synthesis and Assessment Product 2.3 or SAP2.3)

    It has been noted in this thread (and by IPCC) that uncertainties in the direct and indirect effects of aerosol and differences among models concerning the treatment of clouds account for most of the uncertainty in climate sensitivity. The current range is so wide as to be of limited use. We need better estimates of climate sensitivity to make better policy.

    The exec. summary of SAP2.3 asserts that three things can help reduce uncertainties due to limited knowledge about particle properties and impacts:
    “(1) improving quality and coverage of aerosol measurements, (2) achieving more
    effective use of these measurements to constrain model simulation/assimilation and to test model parameterizations, and (3) producing more accurate representation of aerosols and clouds in models.”

    The magnitude of these needs and undertakings does not seem to be widely understood. Again the exec summary reminds us that the differences in climate sensitivities among models is large and necessarily balanced by large differences in aerosol effects (after all the models do largely agree in producing our modern climate). Direct cooling by sulfate varies by a factor of 6 among models. More variation was seen in the treatment of black and organic carbon. Some models ignore indirect effects, others have indirect effects varying by a factor of 9.

    These uncertainties result in estimates of the impact of doubling CO2 that range from 2 to 4.5 degrees. Quoting the Exec Sum of SAP 2.3 again: “Development of new spacebased, field and laboratory instruments will be needed, and in parallel, more realistic simulations of aerosol, cloud and atmospheric processes must be incorporated into models.” Our lack of understanding casts doubt on predictions of future climates. Estimates of anthropogenic contributions to the direct effect vary from -0.7 to -1.5 w m-2. This is not nothing when viewed in the context of net anthropogenic forcing of +1.6 w m-2.

    Note that development of spacebased and field instruments is needed. We still do not have all the measurement tools that are needed!!!!

    The spatial and optical variability of aerosol is huge. The ability to predict abundance and impact is limited. The ability to measure from space is limited. Ground stations providing the physical, chemical and optical characterizations are limited. The RC posts have been good, but limited. But the GCR goofyness is the least of the worries about aerosol. The fundamentals deserve more attention.

    Chuck Wilson

    Comment by James C. Wilson — 26 Apr 2009 @ 1:48 AM

  90. Dear RC

    I’ve just had chance to have a proper read through the Drew Shindell post. I have a few initial questions

    1. In the Abstract to their paper, Shindell & Faluvegi refer to “historical emission estimates”. Is there a source for these estimates.
    2. Due to the complex nature of it’s absorption properties, increases in CO2 results in a logarithmic response. What about aerosols? Can we assume a linear response. For example, if a given level of emissions results in a net forcing of -1 w/m2, can we take it that doubling that level of emissions will result in a net forcing of -2 w/m2 [assume the proportions of BC, SO2 etc remain constant].
    3. Does Drew consider seasonal effects – and what are they? For example, the reflective properties of aerosols in the arctic winter would, I assume, be less relevant than during the summer, while the cloud-forming properties might actually result in warming.

    Final question

    4. Would Drew Shindell have any objection to being contacted directly.


    Comment by John Finn — 26 Apr 2009 @ 5:45 AM

  91. #84 Marcus
    #85 Mark

    Thank you for your posts. Yes – I was not considering these aerosols (other than black carbon), H2O, clouds, or ice albedo.

    I can certainly see how those effects could mask or negate the warming due to black carbon.

    However, those numbers were not presented in the post – so I don’t know what they are.

    Also, since we are speculating – couldn’t all the other effects just cancel out – leaving the entire artic warming due to just black carbon? It doesn’t seem like the data totally exclude that possibility.

    Comment by RickA — 26 Apr 2009 @ 11:33 AM

  92. re: 90

    1. The paper should say. Read it.
    2. Due to the complex nature, a simple answer is not possible.
    3. Ask Drew.
    4. Ask Drew.

    Comment by Mark — 26 Apr 2009 @ 11:39 AM

  93. Click the supplementary info link for the entire list of references. Those should answer the question about sources.

    For the full paper, an academic library will have full access; any public library can borrow the journal for those who want to read it.

    Comment by Hank Roberts — 26 Apr 2009 @ 2:25 PM

  94. “Also, since we are speculating – couldn’t all the other effects just cancel out – leaving the entire artic warming due to just black carbon? It doesn’t seem like the data totally exclude that possibility.”


    Because without the increased CO2, there would have been cooling.

    Whatever that cooling would have been is the magnitude of heating done by CO2.

    The physics may cancel out, but that doesn’t mean that the warming was due to just one. You may as well say “leaving the entire artic warming due to just CO2″. Would you accept that?

    The data excludes the possiblity because the data is the reflection of reality. Reality doesn’t say “Well, we have CO2 and H2O and ice albedo but they all cancel out, so anything else that comes in now is all that’s going to happen”. It lets it ALL happen. It doesn’t cancel out thinks like a student cancelling out elements in two simultaneous equations so that they can work out the value of X and Y.

    Comment by Mark — 26 Apr 2009 @ 3:22 PM

  95. re 86:
    climateprogress ok I guess, but lots of political (as opposed to policy) discussion- and very US-centric.

    re 78
    Thank you for the pointer. Had a good look at the site and it certainly ticks a lot of boxes- I think this is the closest yet.

    Otherwise, the best I’ve found is David Mackay’s:
    But it’s a poor (so far) relation to his book. There’s not much discussion/other views, and definitely UK-centric.

    I guess what we’re looking for is a ‘policy’ blog which is international in outlook, apolitical, and regularly frequented and commented on by working climate scientists. Will keep looking.

    Sorry to continue off topic. But I think there is a real need and finding the right home for this kind of discussion will free up RC for what it does best.

    Comment by Matt — 26 Apr 2009 @ 5:07 PM

  96. Mark Says:
    26 April 2009 at 11:39 AM

    re: 90

    1. The paper should say. Read it.

    I would but the link in the post only links to the abstract which tells me that the “complete document is not available”.

    2. Due to the complex nature, a simple answer is not possible.

    The “complex nature” refers to CO2 not to aerosols. Why should aerosol forcing be “complex”? That’s really what I’m asking.

    3. Ask Drew.

    I would, but I do know that Gavin, for example, has worked with Drew and if I remember correctly has co-authored papers with him. I’m not suggesting that Gavin necessarily speaks for him, but he may be able to suggest the best approach in order to get questions answered.

    4. Ask Drew.

    You are suggesting that I ask Drew if he minds being contacted directly, but to do so I woould have to contact him directly. Drew Shindell posted an article (which is of interest to me) on RC. I would like to know more so I’m just clarifying the position. Is Drew fielding queries via the RC blog or is it best to contact him directly. I fully understand that the regular RC contributors may not necessarily have the answers to my questions.

    ….and why are you responding on their behalf?

    Comment by John Finn — 26 Apr 2009 @ 7:08 PM

  97. #94 Mark

    The physics may cancel out, but that doesn’t mean that the warming was due to just one. You may as well say “leaving the entire artic warming due to just CO2″. Would you accept that?

    If I was told that total artic warming was 1.5C plus or minus .3, and

    CO2 warming for the artic was 1.1C plus or minus .8, then

    yes – I would allow for the possiblity that all of the warming in the artic was due to CO2.

    Because then there would be a small possibility that total CO2 warming was 1.8C (it is within the range), which equals the top end of the total artic warming (1.5 + .3 = 1.8C).

    Of course, that would mean that all the other cooling forcings would have to negate the other warming forcings (black carbon warms and volcanoes cool – maybe all these cancel out).

    Comment by RickA — 26 Apr 2009 @ 9:17 PM

  98. RickA, the physics doesn’t cancel out. They all add up constructively and destructively.

    And you don’t do your addition like that.

    Here’s an example.

    The spread of the hand from fingertip to thumbtip is about 8-10 inches.

    Measuring your height from that “ruler” and going to the nearest “hand” means you’re 8 hands tall.

    The error from that is 0.5 hands from “nearest”. 20% error from the variation of hand sizes and because I didn’t inchworm my way up, another 5% error there from start of one hand to the next.

    So the error is .5+ 8*.25. 2.5hands.

    Your hip is less than 1.5 hands high.

    Does this mean you don’t have a hip???


    So why do you insist that the warming has no CO2 component just because it has error bars.

    Your attempt to use maths this way is in considerable error.

    THEY DO NOT CANCEL OUT. They all sum together. Without one of them, they would not total the same result.

    If you don’t understand you’re willfully ignorant and unworthy of response since you will only hear what you want to hear and trying to educate you is a waste of everyone’s time.

    Comment by Mark — 27 Apr 2009 @ 2:24 AM

  99. NOTE: the ***results*** may cancel out.

    But they don’t stop each element having its effect.

    If you push with a force of 10N on one side of a plate and I push with 10N on the other side of the plate, the ***result*** cancels out.

    This doesn’t mean neither of us are pushing.

    If I push 12N, the result cancels out YOUR push. But it doesn’t mean your push didn’t have an effect and definitely doesn’t mean you didn’t push at all. If you hadn’t been pushing, the resultant force would have been 6x larger.

    Comment by Mark — 27 Apr 2009 @ 2:53 AM

  100. Bill Hunter says:

    “I say that because oscillations likely predate much of this. Below is a link to fish scale deposits. These fishes are very abundant in the eastern pacific and one tends to dominate in rough relationship to ocean SSTs and have done for some time.”

    April Fool’s Day was some time ago, wasn’t it?

    Comment by Ike Solem — 27 Apr 2009 @ 8:49 AM

  101. Bill Hunter’s pointer isn’t foolish, it’s just utterly off-topic.

    Bill, look at the related papers, in particular e.g. this one:

    Impacts of past climate variability on marine ecosystems: Lessons from sediment records

    Yes, nature goes up and down. Add a forcing past the range within which it’s gone up and down, nature takes an excursion to a new state. Both are true.

    But this is about aerosols. Please try to focus.

    Comment by Hank Roberts — 27 Apr 2009 @ 10:09 AM

  102. Hank, Bill, Ike

    I’ve posted a response in the Friday roundup thread to this with regard to species shifts observed in the English Channel over the last ~100 years & also the North Sea.

    Comment by Chris S — 27 Apr 2009 @ 11:43 AM

  103. Gavin,

    Why do you say that the errors in the observed warming, versus the errors in the calculated warming due to aerosol changes are not independent? Theoretically the actual warming due to aerosol changes could be larger than the total actual warming with natural variability accounting for the difference.

    [Response: Yes they could. But the error bars in the Shindell paper were determined all together – it makes no sense to insist that the maximum in one and the minimum in another could have occurred together in the analysis. In fact it is much more likely that the warming attributable to BC+sulphate changes is positively correlated with the total amount of attributable warming. Thus the high end warmings from aerosols occur in situations where there is a large attributable warming. – gavin]

    Comment by Nicolas Nierenberg — 27 Apr 2009 @ 4:53 PM

  104. Gavin,

    First since I don’t have access to the Shindell paper I would like to confirm that they are using the standard observed temperatures. For example GISS or HadCrut and not computing their own new value. Thus the errors in the observed temperatures would be from those independent observations. These would have been determined separately, not together with the errors in the Shindell paper on aerosol warming.

    Would you say that if the true value for aerosol warming were at the high end of the range it is more likely that the true value for actual warming is at the top of the range. In other words that the errors are correlated? This is different than asking if the actual temperature change is correlated with the actual aerosol change.

    In this case then this increases the likelihood that 1.1 of the 1.5 observed value is caused by aerosol changes from what one would guess from simply looking at the overlap of the two error ranges. The delta would tend to persist. Thus if actual warming was 1.8 degrees the likely value for aerosol warming is 1.5 degrees, and if the actual warming was 1.2 degrees then the likely value for aerosol warming is .8 degrees.

    Did I get that right?

    Comment by Nicolas Nierenberg — 27 Apr 2009 @ 5:54 PM

  105. > since I don’t have access to the Shindell paper …

    You don’t have US$32, or a library nearby? Ask for an offprint.

    Asking Gavin to do research values his time less than a bus ticket.

    Comment by Hank Roberts — 28 Apr 2009 @ 9:32 AM

  106. Thanks Hank,

    If I was asking him to do research I apologize. You’re right I could run down to the library. On the other hand he said “the error bars in the Shindell paper were all determined together.” So I thought he would have already had the answer to that question.

    If you’re saying that answering a blog post values his time less than a bus ticket, then that is a different point.

    Comment by Nicolas Nierenberg — 28 Apr 2009 @ 5:44 PM

  107. Dr. Shindell initiated the post. He might be able to send you an offprint if you ask for one. Just sayin’.

    Comment by Hank Roberts — 28 Apr 2009 @ 7:29 PM

  108. I would very much appreciate that.

    Comment by Nicolas Nierenberg — 28 Apr 2009 @ 8:29 PM

  109. Hank, you seem to be very concerned about topic relevance to the blog post, but you must realize that climate science is very interconnected and nothing really exists in isolation, right?

    Aerosols and sea surface temperatures are indeed closely related, indeed that’s something that the Shindell & Faluvegi paper directly relates to, because their results seem to contradict those of another recent Science paper on the aerosol effect on tropical Atlantic SST’s:

    Evan et al. The Role of Aerosols in the Evolution of Tropical North Atlantic Ocean Temperature Anomalies, Science Oct 20 2008″

    Apparently, looking at the Tropical Atlantic in isolation isn’t very useful, at least that’s what I gather. I would like to hear some of the working experts weigh in, though.

    In any case, you quote a paper that refutes your arguments, see this from the abstract:

    In particular, response of higher trophic levels to changes at the base of ecosystems appears to be highly non-linear and shows variations of several orders of magnitude, as exemplified by fish stocks in several areas

    Sea surface temperatures are hardly the only ecological factor controlling the base of ecosystems in the ocean – high sensitivity means that many different factors could be playing roles in any fish-based record – disease, predation, competition, etc.

    And then, you say, “Yes, nature goes up and down. Add a forcing past the range within which it’s gone up and down, nature takes an excursion to a new state. Both are true.”

    That’s a very simplistic statement, isn’t it? Nature is variable, but always up and down? By the same amount? For a specific example, see the Multivariate El Nino / Southern Wobble index

    That’s the best understood ‘natural cycle in the oceans’, and it’s not exactly predictable, is it? Can you predict the decade to come by the decade that passed? Obviously not – sometimes there are several downs before an up, sometimes the opposite, and strength and duration varies all over the place.

    Nevertheless, you have a lot of people running around claiming that the “Pacific Decadal Oscillation is locked into a cool phase” on zero evidence, or the “an enhanced AMO is leading to more hurricanes”, etc.

    Those arguments are not supportable. Yes, there are very periodic natural cycles – the moon’s orbit, say, or the tidal response to the moon’s orbit – which is not quite as predictable as many think, in fact. That doesn’t mean everything in nature is periodic, does it?

    Secondly, any ocean fluctuations or variations are certain to be influenced by global warming energy changes, although we really don’t seem to know how that will play out (with respect to more or fewer El Ninos and La Ninas). In this area, the past is a poor guide to the future.

    Comment by Ike Solem — 28 Apr 2009 @ 9:25 PM

  110. Nicolas, the contact info for the first author is on the journal page.
    Back in the day, we asked for offprints by sending letters including SASEs or postage stamps. These days, maybe you can do it all with electrons. Try.

    Comment by Hank Roberts — 29 Apr 2009 @ 12:03 AM

  111. Ike Solem Says:28 April 2009 at 9:25 PM
    “That’s the best understood ‘natural cycle in the oceans’, and it’s not exactly predictable, is it?”

    Even simpler systems with fewer degrees of freedom and less complicated feedbacks have long been known to behave chaotically.

    “Common intuition suggests that when a circuit is off synchronization the observed output, although not periodic, will be a sum of periodic (intermodulation) components. In fact, at least for a large class of systems we have studied, the output does not have this relatively simple form but is actually chaotic. This paper studies a simple but realistic model for a large class of triggered oscillators. Theory and experiments both confirm that the output shows the properties of sensitivity to initial conditions, nonperiodicity, broad spectrum, and complicated recurrence, that characterize chaotic motion.”
    Synchronization and chaos
    Tang, Y.; Mees, A.; Chua, L. IEEE Transactions on Circuits and Systems, Volume 30, Issue 9, Sep 1983 Page(s): 620 – 626

    It staggers my mind that a handful of op amps and a few dozen resistors and capacitors can demonstrably exhibit chaotic behavior, but many people believe that far more complicated natural systems have “periodic” or “oscillatory” behavior. “Wobbly” is much better descriptor. It’s also straightforward to convert a sinusoidal waveform (like one would expect from Milankovitch cycles) into a sawtooth waveform (approximately like we observe in the ice age temperature record) with a teeny bit of nonlinear feedback; throw in a little “sensitivity to initial conditions, nonperiodicity, broad spectrum, and complicated recurrence,” and viola – Dansgaard-Oeschger events, LIA, MWP, and so on.

    Comment by Brian Dodge — 29 Apr 2009 @ 12:48 AM

  112. Ike, that was a fine attack on those who pretend ENSO/PDO are regular exact repeating pattern to justify argument about climate. Nobody here does. Look for that over at rankexploits.

    Bill Hunter and I just exchanged a few words about sardines. This about sums that up:
    (remove the space after “geo” to make that work — spam filter barfs)

    Yes, it’s all connected; do changes in plankton or sardines affect rainfall in Monterey? Hey, could be.

    Comment by Hank Roberts — 29 Apr 2009 @ 1:25 AM

  113. Glad to see people trying to make others more aware of how we can improve environmental damage. I’m trying to bring awareness by spreading the word on the winners of the Tomorrows World video contest:

    They had a competition over videos about water efficiency and flooding. Living off the West Coast, it’s a very real worry of mine. I think the winners did a great job! Check out their work and forward the link if you like it.

    Comment by Mark — 29 Apr 2009 @ 1:03 PM

  114. Hank says: “Ike, that was a fine attack on those who pretend ENSO/PDO are regular exact repeating pattern to justify argument about climate. Nobody here does.”

    What? That argument has been put forth in realclimate threads over and over and over again, on topics from hurricanes (AMO) to drought (PDO/ENSO). It’s also prevalent over at Dot Earth, see the Don Easterbrook comment:

    This is the cool water phase of the PDO and it isn’t going to change for at least 2-3 decades (at least it never has in the past) and it is unaffected by atmospheric CO2 as shown by the three PDO switches this century that occurred before atmospheric CO2 increased significantly.

    The point, Hank, is that claiming that nature acts like a spring that goes “up and down” until forced into a new state is just plain wrong – a gross oversimplification of complex natural processes, which is usually what denialists do – now that has been a steady pattern for some time. Please don’t propagate such nonsense.

    In any case, let’s get back to the topic of aerosols and their effect on sea surface temperatures, and ‘natural oceanic cycles’. Consider two other much-remarked papers on the subjects:

    Shanahan 2009 Atlantic forcing of persistent drought in West Africa, Science

    There, they use a sediment core from Lake Ghana in West Africa to deduce “African monsoon history” over the past three millennia, which they link to sea surface temperatures… how? Their conclusion is that the AMO is very real, and that modern drought is not anomalous. I would wait and see what more recent coral-based SST reconstructions reveal before putting much faith in that, for example:

    “We present the first absolutely dated and annually-resolved multi-centennial record of Atlantic sea surface temperature… Estimates of externally-forced background variability suggest that anthropogenic forcing can account for most of the warming since 1850 A.D. Multidecadal variations superimposed upon this background disappear prior to 1730 A.D. in favor of interdecadal (15-20 year) variability. This suggests observed multidecadal variability is not persistent and may be difficult to predict. – Saenger et al. 2009”

    Yes, that is aerosol related, not off-topic. Take a look at this paper, also recent:

    Evan et al. 2009 The Role of Aerosols in the Evolution of Tropical North Atlantic Ocean Temperature Anomalies

    TO be brief, their results seem to conflict with those in the original post, i.e.

    So we put idealized forcings from GHGs, aerosols, and ozone in the tropics, mid-latitudes and polar regions to see what would happen. The results showed that the temperature response in the tropics, like the global mean, is only mildly sensitive to the location of forcing.

    The model used by Shindell & Faluvegi is probably a bit more realistic than that used by Evan et al. However, the role of aerosol dust is probably still significant – but is there a good record of the aerosol forcing over the Atlantic over the past few decades? Well, there are estimates:

    “Prospero & Lamb 2003 African droughts and dust transport to the Caribbean: Climate change implications”

    Regression estimates based on long-term rainfall data suggest that dust concentrations were sharply lower during much of the 20th century before 1970, when rainfall was more normal.

    So, the increase in dust after 1970 should have led to cooling Atlantic temperatures, not warming Atlantic temperatures, so how does that work out in the Evan et al. model?

    None of this, of course, eliminates the need to reduce particulate black carbon aerosol concentrations – but to do that, we need to focus on shipping and trucking and coal combustion in the industrialized world, and biomass burning and inefficient internal combustion engines in the developing world (as well as coal, the biggest problem).

    Comment by Ike Solem — 29 Apr 2009 @ 3:13 PM

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