GUEST POST by Fred Moolten
I thought it might be worthwhile to examine more carefully evidence related to a centerpiece of Lindzen’s claim that climate models overstate climate sensitivity by means of “fudge factors” involving aerosols. . . .
In communicating with the public about Climate Change, Richard Lindzen has consistently claimed that climate scientists are overestimating the warming potential of CO2. Central to this claim is his assertion, unqualified by any caveats, that aerosol forcing is “unknown” but is “arbitrarily adjusted” in climate models to make them match observed trends. In particular, he suggests that most often the adjustments deliberately overstate the cooling effect of aerosols to bring the model trends down to the observed trends. We can therefore ask the following relevant questions: (a) Is aerosol forcing “unknown”? (b) Is there acknowledgment by modelers that they adjust the aerosol forcings for the purpose of matching observed trends? (c) If not, are the aerosol parameterizations they make justifiable on some other basis or are they “arbitrary”? (d) Is there independent evidence that can only be reasonably interpreted to mean that the adjustments are made to match observed trends? (e) If choices are made that are not clearly justified by the evidence, are they in the direction of exaggerated aerosol cooling? The answers can help us decide if what Lindzen states as fact is indeed a fact or if Lindzen’s claim in this regard is untruthful.
Before proceeding, it’s worth noting that there is no way to conclusively exclude the possibility that some model choices have on occasion been influenced, perhaps subconsciously, by an intent to match observed temperature trends. We can, however, ask whether this is likely to be true in general, and more importantly whether stating it as an established fact rather than a conjecture can be supported. I suggest that the evidence, taken in total, refutes Lindzen’s statement with high probability.
(a) Is aerosol forcing unknown? A frequent fallacy in blogosphere and some media criticism of mainstream scientific conclusions is the implication that if we don’t know everything, we know nothing. Clearly, if we knew nothing about aerosol forcing, any choices in models would necessarily be “arbitrary”. In fact, however, much is known about aerosol data in general, and in particular its incorporation into models. An example of the latter is found in Schmidt et al 2006, which includes extensive evidence based on physical principles and empirical data. Much also remains to be learned, but the evidence refutes the absolutist proposition that our ignorance is total.
(b) Is there acknowledgment by modelers that they adjust the aerosol forcings for the purpose of matching observed trends? One source on this issue is Gavin Schmidt, in both an exchange on collide-a-scape 334-378 and in the details of how aerosol forcing is developed in the GISS E model described in Schmidt et al 2006 (with coauthors who include modelers Jim Hansen and Andy Lacis). It’s hard to read what Gavin Schmidt wrote without concluding that he flatly rejects any motivation designed to match trends, and that he rejects the notion that such a motivation exists as a general phenomenon among the modelers. (A similar point has been made elsewhere specifically regarding GFDL and CCSM models – see Chapter 5 in the 2008 USCCSP report). What Gavin Schmidt says about how he and other modelers incorporate aerosol forcing into models contradicts Lindzen’s claim about their motivation, unless Gavin is either lying or engaged in self-delusion. His statements of course can’t exclude the possibility of exceptions among a few modelers that Schmidt et al are unaware of.
(c) Are the aerosol parameterizations modelers make justifiable on some empirical basis or are they “arbitrary”? The empirical basis was illustrated in the Schmidt et al reference cited above.
d) Is there independent evidence that can only be reasonably interpreted to mean that the adjustments are made to match observed trends? An important argument that there is some, perhaps unconscious, choice of aerosol parameters made with trends in mind among some modelers comes from papers by Kiehl 2007 and Knutti 2008, both of which report an inverse correlation (a weak one) between model climate sensitivity and total anthropogenic forcing in models that simulate 20th century trends fairly well – a low total forcing reflects primarily strong negative aerosol forcing. Certainly, one explanation for this might be a choice of aerosol forcings made with an eye toward matching observed trends. Since we have statements cited above that trend matching isn’t done, this creates a conflict that would be difficult to resolve if there were not other plausible explanations for the reported inverse correlation. We can explore this possibility.
At least two mechanisms might explain the correlation without invoking specific choices designed to match observed trends. The first is based on the principle that models are parameterized to match existing climatology in the absence of an imposed perturbation such as CO2-mediated forcing. This includes seasonal changes, for example, whereby temperature variation must be explained on the basis of forcings (including aerosols that affect albedo) and feedbacks (which affect climate sensitivity). It is conceivable that different modelers have made choices that permitted that matching but which varied inversely in the relative strengths of forcing and climate sensitivity ,and which then carried over into the trend simulations even though that was not the reason for the choice of parameters. In fact, it is possible that a choice involving a single parameter set could affect both aerosol forcing and sensitivity. For example, Knutti points out that in the case of aerosol indirect effects, both climate sensitivity and these indirect effects depend to some extent on a common hydrology, so that parameterization in that realm could create a correlation of the type observed.
A second mechanism that might contribute to the inverse correlation independent of modeler choice is selection bias. Many models have attempted to hindcast 20th century temperature trends. Those reported by Kiehl 2007 and the subset of CMIP3 models cited by Knutti 2008 do a fairly good job in this regard, but almost certainly others do less well. If, for example, the pairing of climate sensitivity strength and total aerosol forcing in models occurred in a random manner, those that paired them in the same direction (both high or both low) would do poorly and those that paired them inversely would perform better. In preferentially citing the latter, possibly because the poor simulations were less available, these authors have ensured that this type of randomness, if it occurred, would lead to the selective citing of the models that happened to “come out right” even if all models – skillful and unskillful combined – made their pairings at random, or at least independent of observed trends. It would be incumbent on anyone claiming deliberate, non-random pairing to provide direct evidence for that claim, particularly in light of the contradictory statements (see b above) that such deliberate choices were not part of model design. Note, however, that if some models matched temperature trends accurately “by chance”, the apparent accuracy probably overstates the actual skill of the models to make future predictions unless the same compensating errors exist in future simulations.
e) If choices are made that are not clearly justified by the evidence, are they in the direction of exaggerated aerosol cooling? Remember that one of the implications of Lindzen’s “arbitrary adjustments” claim is that they were needed to make the model simulations come out cool enough to match trends without requiring low climate sensitivity. However, if one looks at one of the choices that most significantly affects simulations, it was that most of these older models did not incorporate indirect aerosol effects into their negative forcing estimates. These effects are thought almost universally to be real, albeit fairly small. However, failure to include them makes the models run too warm, contrary to the implication by Lindzen that modelers are trying to overstate climate sensitivity by exaggerating aerosol cooling. Including the indirect effects cools the simulation, and so their absence in the majority of the models implies that the actual climate sensitivity might be higher than estimated from the earlier models. Whatever the practical reasons for excluding indirect aerosol effects, it is hard to see how it could have been motivated by a desire to exaggerate cooling. The omission of indirect effects is likely to be rectified in the current group of models. The absence of indirect effects in most models and their inclusion in others renders interpretation of model/observational relationships problematic. It’s not clear to me that we would see the same inverse relationship if all models had incorporated indirect aerosol effects.
Based on all the above, I find the most plausible interpretation to be the following. (1) Lindzen’s claim that modelers “arbitrarily” adjust “unknown” aerosol forcings to exaggerate the cooling effect of aerosols is unsupportable. (2) There is no convincing reason to doubt claims from modelers (e.g., Schmidt et al) that choices of aerosol parameters are based on available empirical evidence and are not designed to affect the trend simulations. However, the possibility of exceptions to this generalization among some modelers can’t be excluded. (3) The omission of indirect aerosol effects from models is a choice that would understate rather than exaggerate aerosol cooling. (4) Correlations between aerosol forcing and climate sensitivity are difficult to interpret from model simulations that include indirect effects is some cases but exclude them in others (the majority)*. (5) To the extent the inverse correlation would persist even if indirect effects were uniformly included, it can be explained at least in part without invoking deliberate choices by modelers designed to make simulated trends match observed ones. The assertion by modelers that they don’t engage in that type of “tuning” is not refuted.
*In an email conversation with Dr. Knutti, he informs me that the data from many models are inadequate to determine exactly what went into their forcings, and so categorizing the models may not be possible. Dr. Knutti repeats the inference he drew in his paper that some but not all models were guided by observed trends. My conclusion, based on the above analysis, is that at least many were not, and the possibility that some were is still unproven.
________________________________________
I asked Fred Moolten, whose carefully argued and exhaustively researched comments are a highlight of Climate, Etc, for permission to reproduce his comment on Lindzen as a post. This makes him our first guest poster at IT. Very exciting!
Some relevant links:
(1992), Climate forcing by stratospheric aerosols, Geophys. Res. Lett., 19(15), 1607–1610, doi:10.1029/92GL01620.
Consistency Between Satellite-Derived and Modeled Estimates of the Direct Aerosol Effect,Science 10 July 2009: 325 (5937), 187-190.
I thought it might be worthwhile to examine more carefully evidence related to a centerpiece of Lindzen’s claim that climate models overstate climate sensitivity by means of “fudge factors” involving aerosols. . . .
In communicating with the public about Climate Change, Richard Lindzen has consistently claimed that climate scientists are overestimating the warming potential of CO2. Central to this claim is his assertion, unqualified by any caveats, that aerosol forcing is “unknown” but is “arbitrarily adjusted” in climate models to make them match observed trends. In particular, he suggests that most often the adjustments deliberately overstate the cooling effect of aerosols to bring the model trends down to the observed trends. We can therefore ask the following relevant questions: (a) Is aerosol forcing “unknown”? (b) Is there acknowledgment by modelers that they adjust the aerosol forcings for the purpose of matching observed trends? (c) If not, are the aerosol parameterizations they make justifiable on some other basis or are they “arbitrary”? (d) Is there independent evidence that can only be reasonably interpreted to mean that the adjustments are made to match observed trends? (e) If choices are made that are not clearly justified by the evidence, are they in the direction of exaggerated aerosol cooling? The answers can help us decide if what Lindzen states as fact is indeed a fact or if Lindzen’s claim in this regard is untruthful.
Before proceeding, it’s worth noting that there is no way to conclusively exclude the possibility that some model choices have on occasion been influenced, perhaps subconsciously, by an intent to match observed temperature trends. We can, however, ask whether this is likely to be true in general, and more importantly whether stating it as an established fact rather than a conjecture can be supported. I suggest that the evidence, taken in total, refutes Lindzen’s statement with high probability.
(a) Is aerosol forcing unknown? A frequent fallacy in blogosphere and some media criticism of mainstream scientific conclusions is the implication that if we don’t know everything, we know nothing. Clearly, if we knew nothing about aerosol forcing, any choices in models would necessarily be “arbitrary”. In fact, however, much is known about aerosol data in general, and in particular its incorporation into models. An example of the latter is found in Schmidt et al 2006, which includes extensive evidence based on physical principles and empirical data. Much also remains to be learned, but the evidence refutes the absolutist proposition that our ignorance is total.
(b) Is there acknowledgment by modelers that they adjust the aerosol forcings for the purpose of matching observed trends? One source on this issue is Gavin Schmidt, in both an exchange on collide-a-scape 334-378 and in the details of how aerosol forcing is developed in the GISS E model described in Schmidt et al 2006 (with coauthors who include modelers Jim Hansen and Andy Lacis). It’s hard to read what Gavin Schmidt wrote without concluding that he flatly rejects any motivation designed to match trends, and that he rejects the notion that such a motivation exists as a general phenomenon among the modelers. (A similar point has been made elsewhere specifically regarding GFDL and CCSM models – see Chapter 5 in the 2008 USCCSP report). What Gavin Schmidt says about how he and other modelers incorporate aerosol forcing into models contradicts Lindzen’s claim about their motivation, unless Gavin is either lying or engaged in self-delusion. His statements of course can’t exclude the possibility of exceptions among a few modelers that Schmidt et al are unaware of.
(c) Are the aerosol parameterizations modelers make justifiable on some empirical basis or are they “arbitrary”? The empirical basis was illustrated in the Schmidt et al reference cited above.
d) Is there independent evidence that can only be reasonably interpreted to mean that the adjustments are made to match observed trends? An important argument that there is some, perhaps unconscious, choice of aerosol parameters made with trends in mind among some modelers comes from papers by Kiehl 2007 and Knutti 2008, both of which report an inverse correlation (a weak one) between model climate sensitivity and total anthropogenic forcing in models that simulate 20th century trends fairly well – a low total forcing reflects primarily strong negative aerosol forcing. Certainly, one explanation for this might be a choice of aerosol forcings made with an eye toward matching observed trends. Since we have statements cited above that trend matching isn’t done, this creates a conflict that would be difficult to resolve if there were not other plausible explanations for the reported inverse correlation. We can explore this possibility.
At least two mechanisms might explain the correlation without invoking specific choices designed to match observed trends. The first is based on the principle that models are parameterized to match existing climatology in the absence of an imposed perturbation such as CO2-mediated forcing. This includes seasonal changes, for example, whereby temperature variation must be explained on the basis of forcings (including aerosols that affect albedo) and feedbacks (which affect climate sensitivity). It is conceivable that different modelers have made choices that permitted that matching but which varied inversely in the relative strengths of forcing and climate sensitivity ,and which then carried over into the trend simulations even though that was not the reason for the choice of parameters. In fact, it is possible that a choice involving a single parameter set could affect both aerosol forcing and sensitivity. For example, Knutti points out that in the case of aerosol indirect effects, both climate sensitivity and these indirect effects depend to some extent on a common hydrology, so that parameterization in that realm could create a correlation of the type observed.
A second mechanism that might contribute to the inverse correlation independent of modeler choice is selection bias. Many models have attempted to hindcast 20th century temperature trends. Those reported by Kiehl 2007 and the subset of CMIP3 models cited by Knutti 2008 do a fairly good job in this regard, but almost certainly others do less well. If, for example, the pairing of climate sensitivity strength and total aerosol forcing in models occurred in a random manner, those that paired them in the same direction (both high or both low) would do poorly and those that paired them inversely would perform better. In preferentially citing the latter, possibly because the poor simulations were less available, these authors have ensured that this type of randomness, if it occurred, would lead to the selective citing of the models that happened to “come out right” even if all models – skillful and unskillful combined – made their pairings at random, or at least independent of observed trends. It would be incumbent on anyone claiming deliberate, non-random pairing to provide direct evidence for that claim, particularly in light of the contradictory statements (see b above) that such deliberate choices were not part of model design. Note, however, that if some models matched temperature trends accurately “by chance”, the apparent accuracy probably overstates the actual skill of the models to make future predictions unless the same compensating errors exist in future simulations.
e) If choices are made that are not clearly justified by the evidence, are they in the direction of exaggerated aerosol cooling? Remember that one of the implications of Lindzen’s “arbitrary adjustments” claim is that they were needed to make the model simulations come out cool enough to match trends without requiring low climate sensitivity. However, if one looks at one of the choices that most significantly affects simulations, it was that most of these older models did not incorporate indirect aerosol effects into their negative forcing estimates. These effects are thought almost universally to be real, albeit fairly small. However, failure to include them makes the models run too warm, contrary to the implication by Lindzen that modelers are trying to overstate climate sensitivity by exaggerating aerosol cooling. Including the indirect effects cools the simulation, and so their absence in the majority of the models implies that the actual climate sensitivity might be higher than estimated from the earlier models. Whatever the practical reasons for excluding indirect aerosol effects, it is hard to see how it could have been motivated by a desire to exaggerate cooling. The omission of indirect effects is likely to be rectified in the current group of models. The absence of indirect effects in most models and their inclusion in others renders interpretation of model/observational relationships problematic. It’s not clear to me that we would see the same inverse relationship if all models had incorporated indirect aerosol effects.
Based on all the above, I find the most plausible interpretation to be the following. (1) Lindzen’s claim that modelers “arbitrarily” adjust “unknown” aerosol forcings to exaggerate the cooling effect of aerosols is unsupportable. (2) There is no convincing reason to doubt claims from modelers (e.g., Schmidt et al) that choices of aerosol parameters are based on available empirical evidence and are not designed to affect the trend simulations. However, the possibility of exceptions to this generalization among some modelers can’t be excluded. (3) The omission of indirect aerosol effects from models is a choice that would understate rather than exaggerate aerosol cooling. (4) Correlations between aerosol forcing and climate sensitivity are difficult to interpret from model simulations that include indirect effects is some cases but exclude them in others (the majority)*. (5) To the extent the inverse correlation would persist even if indirect effects were uniformly included, it can be explained at least in part without invoking deliberate choices by modelers designed to make simulated trends match observed ones. The assertion by modelers that they don’t engage in that type of “tuning” is not refuted.
*In an email conversation with Dr. Knutti, he informs me that the data from many models are inadequate to determine exactly what went into their forcings, and so categorizing the models may not be possible. Dr. Knutti repeats the inference he drew in his paper that some but not all models were guided by observed trends. My conclusion, based on the above analysis, is that at least many were not, and the possibility that some were is still unproven.
________________________________________
I asked Fred Moolten, whose carefully argued and exhaustively researched comments are a highlight of Climate, Etc, for permission to reproduce his comment on Lindzen as a post. This makes him our first guest poster at IT. Very exciting!
Some relevant links:
(1992), Climate forcing by stratospheric aerosols, Geophys. Res. Lett., 19(15), 1607–1610, doi:10.1029/92GL01620.
Consistency Between Satellite-Derived and Modeled Estimates of the Direct Aerosol Effect,Science 10 July 2009: 325 (5937), 187-190.
Another examples of how models are bad, bad, bad, unless they say something a "skeptic" wants to hear.
Hey nice job Fred. I'll be back to poke holes in it later. Congratulations Robert on your first guest post and now your first comment ever.
ReplyDelete"now your first comment ever."
DeleteYou show your usual command of the facts, Bill.
Why do you think deniers struggle so much to distinguish what is true from what they simply wish were true? An enduring psychological mystery, indeed.
There is also the possibility that there is a deeper connection between climate sensitvity and aerosol forcing via the model's hydrological cycle. Faster/slower aerosol wash out could be linked to a more or less sensitive hydrological cycle. I think that was mentioned in Knuttis Paper somewhere and there are some people working on this.
ReplyDeleteAnyhow, great job!
Nice post. The one thing it lacks is, perhaps, a link to some paper that summarizes the best _experimental_ estimates of net aerosol forcing (since some contrarians don't believe model results at all): but again, those would show that Lindzen's assumption of zero effect is unsupportable, and my guess is that it would show that models all fall within the experimental bounds, and moreover that the models are not biased towards either the upper or lower end of those bounds (with the exception of models that don't include indirect effects).
ReplyDelete(and Lindzen's assumption of zero heat uptake is also unsupportable)
btw, while the major AOGCM models usually don't tune for historical temperature matching (they're just too big and unwieldy for that to work well, even if they wanted to... remember that they take weeks or months to do a 100 year simulation - there's a reason that most of the tuning/validation is done for current conditions where you only need to run a year or two), there are a couple of exceptions where modelers using less computationally intense models have done exactly that: see, eg, Forest et al.: http://globalchange.mit.edu/files/document/MITJPSPGC_Rpt157.pdf. Note that Forest et al. found a relatively low aerosol forcing and low heat uptake compared to other models, and yet found that climate sensitivity should still be between 2 and 5 degrees.
-MMM
"Nice post. The one thing it lacks is, perhaps, a link to some paper that summarizes the best _experimental_ estimates of net aerosol forcing"
DeleteGood idea. Let me see what I can find.
Good to see that this website is getting more input from other commenters rather than being merely a soap box for you Robert. It remains to be seen if this essentially pro-AGW site can handle divergent views and provide the reasoned sort of balance that Fred does so well.
ReplyDeleteFred,
ReplyDeleteI enjoy reading your comments.
In Hansen et al. 2011 (Earth’s energy imbalance and implications, Atmos. Chem. Phys., 11, 13421–13449, doi:10.5194/acp-11-13421-2011) it is conceded that improving observations of ocean heat content show that climate models are mixing heat heat too efficiently into the deep ocean and as a result underestimate the negative forcing of aerosols.
But why should a discovery that models mix heat too efficiently into the ocean tell us anything at all about the strength of aerosol forcing? Because, according to Hansen, we know from paleocalibration studies that climate sensitivity is 3 +/- 0.5 K per doubling of CO2. (And importantly, I think consensus is against Hansen that paleo studies constrain climate sensitivity more tightly than models.)
So do you not agree that Hansen et al. have arbitrarily adjusted the aerosol forcing in their analysis in order to save a preconceived theory about the climate sensitivity?
Alex - I agree that Hansen's claim - that negative aerosol forcing is higher than usually estimated - is somewhat arbitrary, but as far as I know, it's his personal opinion, and is not incorporated into the GISS models. In other words, he appears to believe that most models underestimate aerosol cooling rather than overestimate it as Lindzen suggests. This includes models that simulate temperature trends fairly well and have a climate sensitivity within the consensus range.
Delete"And importantly, I think consensus is against Hansen that paleo studies constrain climate sensitivity more tightly than models."
DeleteThat requires a pretty selective reading of the literature, Alex. For starters you need to be clear which sort of sensitivity is being discussed.
"Because, according to Hansen, we know from paleocalibration studies that climate sensitivity is 3 +/- 0.5 K per doubling of CO2."
DeleteThat's a big oversimplification of Hansen's thoughts on climate sensitivity. Hansen, like the rest of the people working in the field, seems to be moving towards a threefold estimate of climate sensitivity: transient climate sensitivity, true equilibrium climate sensitivity (which takes hundreds to thousands of years), and what for want of a better word can be called intermediate climate sensitivity, the response in the first few decades to a couple hundred years.
Intermediate climate sensitivity is about 3C. Transient is somewhat lower, depending on how transient you want it. True equilibrium climate sensitivity is higher, >5C. A lot of the apparent disagreement between studies has to do, I would argue, with the way the study methods are structured to show one or another of these different type of sensitivity.
Fred,
DeleteYou write,
"In communicating with the public about Climate Change, Richard Lindzen has consistently claimed that climate scientists are overestimating the warming potential of CO2. Central to this claim is his assertion, unqualified by any caveats, that aerosol forcing is 'unknown' but is 'arbitrarily adjusted' in climate models to make them match observed trends. In particular, he suggests that most often the adjustments deliberately overstate the cooling effect of aerosols to bring the model trends down to the observed trends."
I must object to this restatement of Lindzen's position - and in particular to the phrases "unqualified by any caveats", "aerosol forcing is 'unknown'", "'arbitrarily adjusted' in climate models to make them match observed trends", and "most often the adjustments deliberately overstate the cooling effect of aerosols to bring the model trends down to the observed trends." I think all of these subtly misrepresent Lindzen's actual statements.
In 'Taking greenhouse warming seriously' (Lindzen, 2007) he writes,
"How then, can it be claimed that models are replicating the observed warming? Two matters are invoked. First, observe in Figure 6, that once one goes beyond the first three items, the terms are essentially unknown as illustrated by the large error bars (viz Anderson et al., 2003 and Schwartz et al., 2007, for aerosols). Indeed, a recent paper by Ramanathan et al., (2007) suggests that the warming effect of aerosols may dominate – implying that the sign of the aerosol effect is in question. Thus, they can be used to essentially arbitrarily cancel half the anthropogenic greenhouse forcing (or more) as seen in the last item in Figure 6."
So, firstly, he says "essentially unknown" and not "unknown" and it is not true that he gives no caveats. He means "unknown" in the sense that the uncertainty bars are large and the level of scientific understanding is low, and scientists like even Ramanathan are willing to consider forcings outside the IPCC range. Given all this, it would surely be more of an exaggeration to claim the opposite, and say that the aerosol forcing is "known". If we are forced to say it is somewhere within the IPCC range and because our understanding is low it also could be outside of this range, then it would be a bit ridiculous to claim that we "know" the value for aerosol forcing.
(continued)
DeleteSecondly, I think you interpret Lindzen's general complaint of arbitrary cancellation by aerosols as a more specific accusation of model tuning that he doesn't actually make. He is simply pointing to the fact that climate sensitivity and aerosol forcing compensate to keep climate sensitivity within the IPCC range. Models with low sensitivity DO use higher aerosol forcing; models with higher sensitivity DO use lower aerosol forcing. And, this is an uncontested fact (IPCC TAR; Kiehl, 2007; Knutti, 2008; Schwartz et al. 2010) and Lindzen is pointing to this fact and only this fact, and not to any specific unproven explanation of this fact. In point of fact, Kiehl, Knutti and the IPCC now agree that model developers may have tuned their models to reproduce the 20th century temperature record but Lindzen's point would stand even if this was not true, and Kiehl's result turns out to be caused by sheer accident.
I raise Hansen et al. 2011 because it shows, very clearly, that there is great freedom for scientists to pick and choose among values for the aerosol forcing without their understanding of the climate sensitivity to ever be contradicted. Schwartz 2012 finds that,
"the total forcings over the twentieth century employed in [Gregory and Forster, 2008; Padilla et al. 2011] were lower to considerably lower, 0.89 and 0.43 W m-2, than those obtained with the forcings from the studies examined here; the forcing data set employed by Gregory and Forster is less even than the lower bound of the 'very likely' range for forcing up to 2005 as given by the IPCC..."
I'll give you another example I spotted recently myself. The recent Schmittner et al. 2011 study finds a climate sensitivity of 2.3 K whereas another study around the same time Kohler et al. 2010 got 2.4 K per doubling of CO2. However, they both used completely different values for net forcing and net change in temperature at the LGM. Schmitter used a change in T of 3.8 K whereas Kohler used 5.6 K. To the extent that both studies agree, the agreement is, at best, fortuitous.
The fundamental problem is that with such uncertainty in forcing (from anthropogenic aerosols, volcanic aerosols, cloud effects, and solar irradiance) if the bias of the researcher is to find an answer for climate sensitivity within 2 - 4.5 K, it is very easy to do so.
Finally, you claim that Lindzen says that "most often the adjustments deliberately overstate the cooling effect of aerosols to bring the model trends down to the observed trends." Well, I don't think Lindzen to have ever said this.
I think one of the Lindzen's most important papers - important if you want to understand his views - is 'Climate dynamics and global change' (Lindzen, 1994). I would thoroughly encourage you to read that paper.
(continued)
DeleteREFS
Anderson, T.L., R.J. Charlson, S.E. Schwartz, R. Knutti, O. Boucher, H. Rhode, and
J. Heintzenberg, 2003: Climate forcing by aerosols - a hazy picture. Science, 300, 1103–1104.
Kohler, P. R. Bintanja, H. Fischer, F. Joos, R. Knutti, G. Lohmann, and V. Masson-Delmotte, 2010: What caused Earth’s temperature variations during the last 800,000 years? Data-based..., Quaternary Science Reviews, doi:10.1016/j.quascirev.2009.09.026.
Lindzen, 1994: Climate dynamics and global change, Annu. Rev. Fluid Mech., 26, 353-378.
Lindzen, 2007: Taking greenhouse warming seriously. Energy & Environment, 18, 937-950.
Ramanathan, V., M.V. Ramana, G. Roberts, D. Kim, C. Corrigan, C. Chung & D. Winker, 2007: Warming trends in Asia amplified by brown cloud solar absorption, Nature, 448, 575–578, doi: 10. 1038/nature06019.
Schmittner, A. N.M. Urban, J.D. Shakun, N.M. Mahowald, P.U. Clark, P.J. Bartlein, A.C. Mix, and A. Rosell-Mele, "Climate Sensitivity Estimated from Temperature Reconstructions of the Last Glacial Maximum", Science, vol. 334, 2011, pp. 1385-1388.
Schwartz, S.E., R.J. Charlson, and H. Rhode, 2007: Quantifying climate change – too rosy a
picture? Nature Reports Climate Change, 2, 23–24.
Schwartz et al. 2010: Why Hasn’t Earth Warmed as Much as Expected?, J. Clim., DOI: 10.1175/2009JCLI3461.1.
Schwartz, 2012: Determination of Earth’s transient and equilibrium climate sensitivities from observations over the twentieth century: Strong dependence on assumed forcing, Surveys in Geophysics.
Alex - I'm afraid your statements are simply wrong. I quoted Lindzen exactly, and in context, for most of the words I used in quotation marks. He did say aerosol forcing was "unknown", without qualifying adjectives, and he did say it was "arbitrarily adjusted" to match temperature trends, and he did say that it was a "fudge factor", and he has said on many occasions that the adjustments were used to make the models run cooler because without them, climate sensitivity would be too high.
DeleteI think you should probably not spend your energy defending Lindzen, because regardless of some of the other realities I've discussed in my comment, Lindzen's claims aren't really defensible.
I agree that you have raised other points of interest, but I think most of these have already been addressed by me and others in Judy Curry's blog. If they come up again there, we can probably continue the discussion in that venue.
Hmm - I forgot the distinction between adverbs and adjectives. Lindzen said aerosol forcing was "unknown" without any qualifying adverbs, not adjectives, because "essentially" is an adverb.
DeleteFred,
DeleteI guess the question is are you making a strong claim that what Lindzen believes as understood from his published writings is wrong, or a weak claim that what he believes may or may not be wrong, but what he said specifically in the House of Commons slides is wrong. On the weak claim, I agree (after now reading it). He goes too far. And I don't think he accurately represents his own arguments there. While it is unfortunate that he would be loose in his statements in this presentation, the more interesting question is still his actual views as expressed in the peer reviewed literature. I don't think you have addressed this.
Alex - To summarize my post above and many comments I've made in Judy Curry's blog, I believe that what Lindzen said to the House of Commons was wrong, and that his views as expressed in the literature are ones I disagree with without being able to pronounce them "wrong".
DeleteThe myth about aerosol tuning was popularized by Judith Curry, despite people from the climate modeling community telling her she was wrong.
ReplyDeleteIt's pretty astounding that she continues to claim that "in the AR4 simulations, most of the aerosol “data” was generated by inverse modeling" even today, after her Uncertainty Monster paper was demolished by Hegerl et al.
Steve Bloom,
ReplyDeleteHansen is talking about equilibrium "fast-feedback climate sensitivity". "Fast feedbacks" are taken to be the water vapour, cloud, aerosol, and snow-ice-albedo feedback. He appears to exclude the vegetation feedback and GHG feedback as slow feedbacks. Hansen claims that "paleoclimate data constrain fast-feedback climate sensitivity to ... 3 ± 0.5°C for doubled CO2". This is in contrast to the IPCC which claims that the same quantity is constrained by all methods within 2 - 4.5°C.
To see that Hansen's view is an outlier you might look at the IPCC Fig. 9.20 which shows the ranges of climate sensitivity from a variety of methods in the literature.
The recent paper that I mentioned above - Kohler et al. 2010 - may be one of the most thorough reviews of the forcing data over the LGM period. It is cited frequently in the AR5 ZOD. These authors conclude that,
Climate sensitivity in our analysis is very likely in the range 1.4–5.2 K (5–95%), the most likely value is 2.4 K, well within the consensus range of 2–4.5 K based on multiple lines of evidence (Solomon et al., 2007; Knutti and Hegerl, 2008). Second, the uncertainties are large if all forcings and uncertainties are considered properly, and the LGM does not provide a strong constraint on sensitivity. Low values of climate sensitivities (i.e. almost no net feedbacks ... are unlikely but possible. ... Values above 6 K are not supported by this analysis, but the plausible range still exceeds the range covered by general circulation models (2.1–4.4 K).
And as I pointed out above, Kohler et al. get a much higher range of climate sensitivity than they would have got if they had considered Schmittner's method for estimating the LGM cooling. They also use a highly uncertain "scaling factor" that increases their climate sensitivity by about 10-20 % or so to account for the belief that climate sensitivity is state-dependent (meaning not the same now as it was at the LGM).
"Indeed, a recent paper by Ramanathan et al., (2007) suggests that the warming effect of aerosols may dominate – implying that the sign of the aerosol effect is in question."
ReplyDeleteI don't remember that from any of Ramanathan's paper. The reference you cite above only considers Asian effects - far from representative of global levels of aerosols. The famous "0.9 W/m2 warming from black carbon" Ramanathan and Carmichael paper actually finds a net negative all-aerosol forcing of -1.4 W/m2 (http://courses.washington.edu/pcc588/readings/ramanathan_carmichael_2008.pdf).
So it appears that Lindzen is wrong again. Somewhat unsurprisingly.
-MMM
Wisely, Professor Lindzen is entirely silent on the issue of aerosol forcing when speaking to an open-minded public such as our antipodean friends on the underside of the Earth:
ReplyDeleteJones:
If C02 caused warming, how could human production of C02 be catastrophic, when nature produces what, 32 times as much as human beings; 97% of C02 in the world is naturally produced.
Lindzen:
Well, yeah, you’re, you’re addressing the issue of how can one regard something essential to life as a pollutant, and, uh, I don’t know the answer to that, it seems absurd but on the other hand you can get many people to sign on to government control of uh, dihydrogen oxide, ah because they don’t know it’s water.
Jones:
That’s it. I mean just taking the maths of it, I mean you’re, you’re an eminent scientist; is it true that the proportion of the Earth’s annual production of C02 is about 3% produced by human beings and 97% roughly produced by nature?
Lindzen:
Well that’s correct, that’s correct; the (talkover) argument often is presented that the natural part is in balance and our contribution is imbalancing, unbalancing the system and so that’s leading to a rise. Uh, that’s an arguably possible situation but in point of fact there’s limited evidence of that and the merest uh misunderstanding of the 97% could easily overbalance man’s contribution but to be honest that is not an issue that is known at present and I would argue it’s not even the central issue.
Don't waste your precious mind worrying about aerosol forcing! Perorations on aerosols are to put the cart before the horse; we don't even know if we're changing the concentration of C02 in the atmosphere. So says the distinguished Professor Richard Lindzen, often found in worthy company of British Peers.
I admit to some sympathy. Who hasn't found themselves, in conversation with a friendly fellow-traveler, trying to gently correct their ignorance while finding the grains of truth in their words?
DeleteBut the London presentation, written, prepared, and delivered in cold blood, is another story. He lied deliberately, if we are to credit him with any competence in his own field. I and I think a lot of people are still a little stunned by how bad he's gotten
Thank you very much for sharing. nice post
ReplyDeleteac duct cleaning Lake Worth Corridor fl
This post is idiotic. Aerosol forcings are completely arbitrary in every model because aerosol levels are totally unknown in the past. How do models match up with the "pause" in warming from 1940-70. Aerosol levels are not known during the time period. Who cares if you now the sensivity. How do you know the actual amount of aerosol in the air that come from volcanos and particles. You don't.
ReplyDelete"Aerosol forcings are completely arbitrary in every model because aerosol levels are totally unknown in the past."
DeleteSo you think there is no trace of, say, volcanic eruptions that threw up aerosols in the past?
You don't think the aerosols maybe fell to earth eventually, and you might be able to learn about them by studying, say, ice cores, or lake sediments?
This is the classic problem with climate deniers: you project your own ignorance and stupidity upon the world, and specifically scientists.
When you say "You don't [know]" what you actually mean is that YOU don't know. Because you're ignorant. And not very bright. Fortunately, climate scientists are smarter than you. :)
Sunday, January 26, 2014
ReplyDeleteSettled Science: New paper finds effect of man on climate is "highly uncertain"
A new paper published in Science finds "the radiative forcing (that is, the perturbation to Earth's energy budget) caused by human activities is highly uncertain, making it difficult to predict the extent of global warming."