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Aerosols: The Last Frontier?

Filed under: — group @ 21 February 2007 - (Português)

Guest commentary from Juliane Fry, UC Berkeley

The recently released IPCC 2007 Fourth Assessment Report Summary for Policymakers reminds us that aerosols remain the least understood component of the climate system. Aerosols are solid or liquid particles suspended in the atmosphere, consisting of (in rough order of abundance): sea salt, mineral dust, inorganic salts such as ammonium sulfate (which has natural as well as anthropogenic sources from e.g. coal burning), and carbonaceous aerosol such as soot, plant emissions, and incompletely combusted fossil fuel. As should be apparent from this list, there are many natural sources of aerosol, but changes have been observed in particular, in the atmospheric loading of carbonaceous aerosol and sulphates, which originate in part from fossil fuel burning. While a relatively minor part of the overall aerosol mass, changes in the anthropogenic portion of aerosols since 1750 have resulted in a globally averaged net radiative forcing of roughly -1.2 W/m2, in comparison to the overall average CO2 forcing of +1.66 W/m2.

Figure SPM-2, shown here, compares the radiative forcing for greenhouse gases and other climate forcing agents, along with an assessment of the level of scientific understanding (“LOSU”) for each component. In this figure, it is clear that while aerosols contribute the largest negative (cooling) radiative forcing, the level of scientific understanding of their climate influence is “low” to “medium-low”. The aerosol effects are split into two categories: (1) direct effects, meaning the scattering or absorption of radiation by aerosols influencing the net amount of energy reaching the Earth’s surface, and (2) indirect effects, such as the cloud albedo effect, referring to how the presence of aerosol increases cloud reflectivity by providing a larger number of nuclei for cloud droplets, reducing the amount of energy reaching the surface. This is a step up from the last report, where the LOSU for aerosols was very low to low, and no most likely value was assigned at all for the ‘indirect’ part.

This figure also visually hints at why improving our understanding of aerosol’s role in climate is so important: while overall net radiative forcing is positive (warming), aerosols provide the dominant negative (cooling) forcings. Hence, the aerosol currently in our atmosphere is acting to mask some of the greenhouse gas-induced warming. This means that as we get our act together to reduce fossil fuel use to improve air quality and address global warming, we need to be mindful of how changes in emissions will impact aerosol concentrations and composition.

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

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

So, what do we need to learn about aerosol to narrow those error bars in Figure SPM-2? To accurately model aerosols’ climate impact, we need to know about the whole lifespan of the aerosols: their diverse sources, aging processes (and how those affect radiative properties), how they mix together and the mechanisms and timescales for its removal from the atmosphere. As the IPCC 2007 4AR will make clear, we’ve come a long way in our understanding of atmospheric aerosol, but there is still plenty of room for improvement.


184 Responses to “Aerosols: The Last Frontier?”

  1. 101
    Ike Solem says:

    RE#98,
    There is a far better news report available on the global dimming issue than Sherwood Idso’s “CO2 science” magazine, which really represents the worst of the worst when it comes to accurate scientific information on global warming. Try http://abcnews.go.com/Technology/story?id=1566139 (Feb 2006)

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

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

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

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

    Groups like CO2science.org don’t seem to want better data – they want uncertainties which they can use to question the reality of anthropogenic global warming. Paleoclimate and computer modeling studies are critically important, but the strongest evidence continues to come from real-time comprehensive data collection from the oceans and from space. The lack of funds for climate satellites and ocean sensors that would help answer these questions seems like a stalling tactic – and is a travesty.

  2. 102
    Charles Muller says:

    #98 Gavin response

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

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

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

  3. 103
    Charles Muller says:

    #101

    To be fair, G. Stanhill mentions “six isolated sites”, but also refers to a bibliography of 70 papers or so on global dimming / brightening :
    http://www.greenhouse.crc.org.au/crc/research/c2_bibliog.htm

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

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

  4. 104
    Daniel Morris says:

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

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

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

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

    [Response: See our previous posts for the relative roles of water and CO2: http://www.realclimate.org/index.php/archives/2005/04/water-vapour-feedback-or-forcing/ . Without CO2, the majority of the current greenhouse effect would disappear, but it's difficult to be precise since you very quickly get into regimes where the physics is not likely to be well captured in GCMs. -gavin ]

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

  5. 105
    Ike Solem says:

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

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

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

  6. 106
    Dennis Wingo says:

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

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

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

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

  7. 107

    Just a little heads up on Dennis Wingo.

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

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

  8. 108
    Charles Muller says:

    #105

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

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

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

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

  9. 109
    C. W. Magee says:

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

  10. 110
    Dennis Wingo says:

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

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

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

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

  11. 111
    Ike Solem says:

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

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

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

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

    What is needed is the Deep Space Climate Observatory, which was designed to hover over the sunlit side of the Earth for long periods, at Lagrange 1 between the sun and the Earth. See http://www.iht.com/articles/2006/01/15/opinion/edpark.php for a description of how this project was killed. Incidentally, none of the sites like CO2science or AEI even mention the DSCO.

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

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

  12. 112
    Hank Roberts says:

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

    http://www.acrim.com/RESULTS/Earth%20Observatory/earth_obs_fig9.pdf

  13. 113
    Charles Muller says:

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

  14. 114

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

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

  15. 115
    Nick Gotts says:

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

  16. 116

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

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

  17. 117
    Charles Muller says:

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

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

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

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

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

  18. 118
    Hank Roberts says:

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

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

  19. 119
    Dennis Wingo says:

    Hank

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

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

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

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

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

  20. 120
    Hank Roberts says:

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

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

  21. 121

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

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

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

    [Response: We discussed this in some detail previously: http://www.realclimate.org/index.php/archives/2005/07/climate-sensitivity-and-aerosol-forcings/ - it's a pretty prevalent confusion. -gavin]

  22. 122

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

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

  23. 123
    Ike Solem says:

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

  24. 124
    Dennis Wingo says:

    Barton

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

  25. 125
    Charles Muller says:

    #121 and Gavin link

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

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

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

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

  26. 126
    Blair Dowden says:

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

  27. 127
    Dennis Wingo says:

    Barton

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

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

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

    And this:

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

    **********

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

    Reference:

    http://blue.atmos.colostate.edu/publications/pdf/Hansen-Science.pdf

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

    Another question that I have not seen addressed anywhere.

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

    Climate is a facinating subject.

    [Response: Context. This is an excerpt from a rejected comment from Pielke and Christy on a Science paper I was co-author on, and for which our reply is also available: http://blue.atmos.colostate.edu/publications/pdf/1116592Hansen.pdf along with the comments from the reviewers of the exchange: http://blue.atmos.colostate.edu/publications/pdf/Pielke_reviews.pdf - gavin]

  28. 128
    Dennis Wingo says:

    Thanks for that.

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

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

    ****

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

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

  29. 129
    Dennis Wingo says:

    Hank

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

  30. 130
    Dennis Wingo says:

    Ray

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

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

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

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

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

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

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

  31. 131

    [Note to the Moderators]

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

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

  32. 132
    Hank Roberts says:

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

  33. 133
    Marco Parigi says:

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

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

  34. 134

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

    So is mine.

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

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

  35. 135

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

    Huh? What? Come again?

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

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

  36. 136
    Charles Muller says:

    (OT)

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

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

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

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

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

  37. 137
    Dennis Wingo says:

    Barton

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

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

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

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

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

  38. 138
    teacher ocean says:

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

  39. 139

    Science is based on organized skepticism

    Actually, no, science is based upon evidence.

    Even skepticism must be based upon evidence.

  40. 140
    teacher ocean says:

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

  41. 141
    Hank Roberts says:

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

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

    Later qualified:

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

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

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

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

    > The typical hurricane delivers an average power output of
    > about 50-200 terawatts during its lifetime…
    wte.cbll.net/energy/renewables

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

  42. 142

    Re #136 (comment):

    Raypierre:

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

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

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

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

  43. 143

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

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

  44. 144

    a lawyer would say justice is based on evidence

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

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

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

  45. 145
    Joseph O'Sullivan says:

    “a lawyer would say justice is based on evidence”

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

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

  46. 146
    Lynn Vincentnathan says:

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

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

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

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

  47. 147

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

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

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

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

  48. 148

    Re#146

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

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

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

  49. 149
    Blair Dowden says:

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

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

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

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

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

  50. 150

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

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


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