Arnold Kling  

Who Are the Climate Scientists?

New Working Papers of Interest... Political Long Tail, Revisited...

Before I get to that, here is a BBC rebuttal to climate skeptics.

The statement that water vapour is "98% of the greenhouse effect" is simply false. In fact, it does about 50% of the work; clouds add another 25%, with CO2 and the other greenhouse gases contributing the remaining quarter. Water vapour concentrations are increasing in response to rising temperatures, and there is evidence that this is adding to warming, for example in Europe. The fact that water vapour is a feedback is included in all climate models.

This is to counter the alleged skeptic argument that "Water vapour is the most important greenhouse gas, accounting for about 98% of all warming."

What I have read is that (a) water vapor is 98 percent of all greenhouse gases, not that (b) it accounts for 98 percent of all warming. So it is not clear to me whether they mean to refute (a) or (b). In principle, water vapor could be 98 percent of all greenhouse gases and CO2 emissions could account for 100 percent of all the warming.

My view of the water vapor issue is that it makes models of global warming highly sensitive to assumptions about how water vapor responds to an exogenous rise in CO2. If you assume a positive response, then you will get a lot more global warming in response to emissions than if you assume that water vapor remains constant.

Bruce Charlton points me to this analysis of contributors to the latest IPCC report.

Of the 51 UK contributors to the report, there were 5 economists, 3 epidemiologists, 5 who were either zoologists, entomologists, or biologists. 5 worked in civil engineering or risk management / insurance. 7 had specialisms in physical geography (we gave the benefit of the doubt to some academics whose profiles weren't clear about whether they are physical or human geographers). And just 10 have specialisms in geophysics, climate science or modelling, or hydrology. But there were 15 who could only be described as social scientists. If we take the view that economics is a social science, that makes 20 social scientists.

...Of the 70 US contributors, there were 7 economists, 13 social scientists, 3 epidemiologists, 10 biologists/ecologists, 5 engineers, 2 modellers/statisticians, 1 full-time activist (and 1 part time), 5 were in public health and policy, and 4 were unknowns. 17 worked in earth/atmospheric sciences.

I'm thinking that my scientific qualifications to discuss global warming are about on par with those of the median contributor to the IPCC report. To be fair, there could be hundreds or even thousands of climate scientists who did not contribute to the IPCC report but who support its findings.

Actually, I don't need a lot of scientists to convince me to buy into the IPCC report. It might only take just one. All I ask is that one climate scientist give me a list of the empirical findings that are persuasive that CO2 emissions are the cause of global warming. So far, all I am getting is the broad trend of higher CO2, the rise in temperatures since 1980, and the climate models that link the two by design.

UPDATE: A commenter finally points me to something helpful, namely

UPDATE 2: See below (more citations added).

this history of climate science.

A final nail in the skeptics' coffin came in 2005, when a team compared computer calculations with long-term measurements of temperatures in the world's ocean basins (it was not in the air but the massive oceans, after all, that most of any heat added soon wound up). In each separate ocean basin, they showed a close match between observations of rising temperatures at particular depths, and calculations of where the greenhouse effect should appear. This was telling evidence that the computer models were on the right track. Nothing but greenhouse gases could produce the observed ocean warming — and other changes that were now showing up in many parts of the world, as predicted.

AHA! Something that sounds like evidence for a greenhouse effect, as opposed to solar activity or somesuch.

Another commenter recommends this chapter of the IPCC report. I wish the writing were punchier, as in the report described below.

this paper, recommended by another commenter, is an alternative reading of the state of climate science today, from the Fraser Institute, a Canadian think tank that leans libertarian. This excerpt from the alternative report captures my concern with much of the evidence as presented in the IPCC chapter cited above:

The term “attribution” means consistency with a climate model-generated scenario, rather than formal proof of causality. The same data could be consistent with contradictory hypotheses, including large or small greenhouse warming.

Typically, the IPCC chapter will show a graph comparing the actual results to model simulations with and without a CO2 effect, with the latter fitting the data better. That strikes me as closer to proof by assumption than proof by empirical evidence.

Here is an analogy: Suppose, hypothetically, that ability is what affects earnings, and once you control for ability education does nothing. But your model only includes education, which is also correlated with ability, which you don't include. You can say that model simulations that incorporate education work better than simulations that don't. Ergo, education matters. But that is a relationship you imposed on the data, by not including ability.

The IPCC attribution methodology only works if the models have included and properly specified all of the factors affecting temperature that have a positive trend in the last thirty years. It is unlikely that the models are so complete.

Below are some more excerpts from the contrarian report. I feel badly not giving equal time to the IPCC chapter, but as I said, the writing there is more turgid. Substantively, the IPCC chapter might be as good or better than the contrarian report. It would be interesting to see the issues debated.

studies have shown that the spatial pattern of warming trends over land correlate strongly with the distribution of industrial activity, even though such a correlation is not predicted by climate models (e.g., de Laat and Maurellis 2004, 2006).

...There is no significant warming in the tropical troposphere, which accounts for half the world's lower atmosphere. This is where models that assume a strong influence of greenhouse gases forecast some of the most rapid warming should occur.

...The Third Assessment Report drew attention to the declining Diurnal Temperature Range (DTR) as evidence of global warming (Working Group 1 Summary for Policymakers, page 1). The decline in the DTR has now ceased, and appears to be growing in most places.

...There are differences in linear trends of tropospheric temperatures between the high latitudes of the Northern and Southern Hemispheres that are not consistent with computer model projections.

...At the global scale, some broad predictions made 30 years ago about the possible response to increased CO2 concentration in the atmosphere, namely increased average tropospheric temperature, decreased average stratospheric temperature and a more rapid hydrological cycle, are consistent with data that have emerged since then

...Models tuned to “perfectly” reproduce an observed mean climate state have nonetheless shown only a weak ability to predict subsequent climatic conditions. It is not possible to say which, if any, of today’s climate models are reliable for climate prediction and forecasting.

...Quantitatively, individual climate models are typically unable to reproduce the observed mean surface temperature to better than +/- 3 kelvin, with worse performance near the poles. They are also unable to reproduce the onset of ice ages. The margin of present-day error is similar to the size of the projected global warming trend over a century.

Comments and Sharing

COMMENTS (24 to date)
Matt writes:

This link has a good historical view of the relationship between CO2 and water gas in climate. The important point to remember is that we do not have on homogeneous atmosphere but a layered atmosphere, the two gases act at different levels.

David writes:

[Comment removed for providing false email address. Please email the to request restoring this comment. A valid email address is required to post comments to EconLog.--Econlib Ed.]

Ajay writes:

And I suspect that's all you'll get, Arnold, as you no doubt imply.

Chandan writes: know whether CO2 really heats up environment, simply go to a green house lab/plant, stay there for couple of hours, and measure changes in mercury!

Kevin Dick writes:

@David. You should click through to the source for the quote. It's a response to Andrew Dessler claiming that the climate skeptics are not qualified scientists. The point is that many of the IPCC contributors don't clear the bar that Dessler sets for the skeptics.

Buzzcut writes:

The statement that water vapour is "98% of the greenhouse effect" is simply false. In fact, it does about 50% of the work; clouds add another 25%,

Uhh, clouds are water vapor.

Like, duh.

So water vapor is 75% of the greenhouse effect, not 98%. It's still a WHOLE LOT MORE than CO2.

Jim writes:

"All I ask is that one climate scientist give me a list of the empirical findings that are persuasive that CO2 emissions are the cause of global warming."

You say this like you've actually asked some climate scientists and they've refused to answer. Can you tell us who? Or have you stuck to these chin-stroking blog posts in the expectation that climate scientists would rush to furnish you with the evidence? I don't expect economists to personally supply me with evidence - I go and find it myself. Has it not occured to you to maybe read a few articles on the subject?

"the climate models that link the two by design."

If you're suggesting that the idea of CO2 as a significant greenhouse gas is some sort of sinister fiddle invented by conspiring climate scientists then I think you need to go back to school. If not, then exactly what kind of 'design' effect are you alleging? I'd appreciate some clarity on this point - vague insinuation isn't good enough.

If you're genuinely interested in assessing the empirical evidence then as a layman I suggest you might start here and report back to us.

ErikR writes:

Actually, clouds are not water vapor. Water vapor is an invisible gas (for example, on a humid day there is a lot of water vapor in the air but you cannot see it). Clouds are condensation (particles of liquid water) suspended in the air.

Al T writes:

Here's a link to the blog of one of the reviewers:

He often endorses the view of this websites:

aaron writes:

Do you know how long it would take the oceans to heat to the point they heated the air?! (and Ocean surfaces have been stable or cooling, see Pielke.)

aaron writes:

And, increasing water vapor could cause cooling. (Thawing and evaporation absorbe energy, condensation and freezing release it.)

Kevin Dick writes:


I think you'll have to settle for a more nuanced answer than simply whether CO2 increases temperature. From what I've seen, many if not most reputable skeptics accept that, all other things being equal, increasing CO2 will result in some temperature increase (see: It's an issue of what the actual response curve looks like, the amount of temperature variance explainable by CO2, and the ultimate ecological effects of the warming. Then there's issue of forecast accuracy of the models out 20, 50, and 100 years.

Imagine a rough economic analogy. All other things being equal, printing more money increases inflation, right? And too much inflation is bad, right? So will printing X dollars every year cause a huge depression in 20 or 50 years? What's the forecast for GDP 20, 50, and 100 years out with specific "loose" and "tight" policies? What do the error bars look like?

As for the specific instance of the models being right that you found, should this surprise you? Given any halfway decent macroeconomic model, can't you find some things it predicts correctly?

But does the model get the big things right? What did the 1995 models (2nd IPCC) predict about CO2 levels and temperatures today? That should at least allow us to calculate error bars for the far future forecasts.

Gary Rogers writes:

Doesn't the whole argument on the side of global warming come down to asking for hundreds of billions of dollars to fight a problem that, even if you believe in it, it is already too late to fix? Unless someone can think farther ahead than this, I am not ready to spend too much time arguing the details of whether or not it is water vapor or CO2 that should contribute more to the model. Maybe someone could propose a real solution to this problem, that they seem to understand so well. This would be so much better than trying to force everyone else into some arbitrary CO2 emission level that their own models say is an inadequate solution. When I weigh the costs of the solution against the probability that global warming is truly a problem, I still find the balance on the side of skepticism.

aaron writes:

[You'll really like where that leads, he factors education into warming trends.]

dearieme writes:

I'm not a "climate scientist", although I should add that if by "scientist" one means people who perform controlled experiments, there is no such thing as a climate scientist. Be that as it may, I have done quite a bit of mathematical modelling of chemico-physical processes, having started in 1967. Based on my experience, I laugh at the absurd lack of a sense of proportion that lets people claim that huge sums of money should be spent on the "evidence" of their mathematical modelling. But please don't think that I am a sceptic - I started as one, attributing the Global Warming nonsense to hubris and incompetence. I then became a cynic, however, when I learnt that there does seem to be a combination of recklessness and dishonesty being deployed. I suppose that I am now a Global Warming atheist - accepting that this business is now about Faith, not evidence. Heretics beware.

Jim writes:

"It is unlikely that the models are so complete."

What do you suggest is excluded? Please be specific - if your only criticism is that there must be 'unknown unknowns' it isn't going to be very convincing, in fact it would look exactly like the argument of last resort. Oh and please don't assume that your experience in economic modelling is necessarily relevant - it is clearly more than possible that modelling human societies will be far more difficult and unpredictable than modelling physical and chemical processes, so the uncertainty learned through experience in one needn't necessarily be applied with the same force to the other. Finally, I'd like to suggest again that you actually talk to some climate scientists about this rather then engaging in more empty speculation.

"I feel badly not giving equal time to the IPCC chapter, but as I said, the writing there is more turgid."

Oh come on. If you want your criticisms to be taken seriously, then make the effort. I'm honestly surprised you think so little of your readers to fob us off like this. You asked for a list of evidence, you got it, and now you're not interested?

"It would be interesting to see the issues debated."

It really, really would.

Brad writes:

I realize that 1998 was a hot year, but do the models predict we should have seen continued warming over the last decade? Is 10 years to short a time period to draw any conclusions? If we don't see any warming over the next 5 or 10 years do we begin to discount AGW? Can anyone point me in the right direction? Thanks

Geoffrey writes:

I read the top 10 counters to skeptics and was horribly unimpressed. I agree that I may be suffering by some confirmation bias.

Some counters they don’t even answer.

For example “with CO2 and the other greenhouse gases contributing the remaining quarter.”
The question was how important was CO2 and the authors lump it in the “other” category. When I give presentations at work anything in the “other” category is not that important.

#7 about the CO2 rise coming a hundred years after past temperature rises is unimportant!!!
Pleeease…How can they dismiss it like that. That’s a real big causality issue that they don’t seem to want to address (goes too directly to their core position)

I personally not all that hyped up that the current climate models have large error bars.
However please show me some evidence that the trends of increased CO2 increase global temperatures. I haven’t seen it..

(Note: I believe in some global warming. I am a skeptic on human caused global warming. I am a very very strong skeptic that mandated government cures for global warming will have any positive effect on human welfare; I believe a strong negative effect)

aaron writes:

Brad, sorry but I'm of little help. The thing is that things are much more ambiguous as popular culture would lead us to believe, the emperical evidence is very weak regarding feedbacks. Feedbacks are the basis for any significant amount of warming (and variance is much larger than the trend, including feedbacks). That's not to say they are impossible, it's just that they are not very likely (or more accuratly, very far from likely).

Visit, by Nir Shaviv. The effects of CRF on low cloud cover seems pretty solid. Here are some starters: CO2 or Solar; Cosmic rays and Climate; A Primer on Climate Sensitivity. This would explain away a lot of the forcing attributed to CO2.

I recommend reading the comments.

Also, in the recent past a paper was written that was presented as a discrediting the CRF link, however it did no such thing. It was entirely consistent with Shaviv's theory which was that CRF could explain over half (about 2/3 IIRC) of the warming in first half of the century, but only about 1/3 to half of the warming in the second half of the century. This comment may explain a bit of the misunderstanding. Critics also try to claim that there is little relationship by lumping all cosmic rays togher when the type of CR is crucial. The type of CR hitting the earth varies, it is the high energy rays that affect low cloud cover.

They are beyond my understanding but, somewhere Nir explains lags in the effect of the absense of low cloud cover (If my understanding is correct, the theory goes that periods of a dearth of low cloud cover have a cumulative affect on warming, and combinded with these lags, it's the unprecidented high solar activity over the past centruy that has driven temps up beyond the normal fluctuation, in addition to GHG warming and unknows-- the majority of climate change). And after CRF increased after 2000, we did see a flattening, and likely a slight cooling.

As for seeing no warming, I don't think that would mean much, but a cooling could mean a lot since the theory of global warming is dependant on the retention of heat emmitted from the earth (not absorption from incoming radiation). There are many factors that affect the absorption of solar radiation, some will be dependent on GHG warming and other not (most are probably random). There are also many variable factors that affect retention of heat that are much larger than AGHGs. There are also many possible feed backs, both for solar and CO2 factors. I believe that I've read for some unkown reason, the characteristics of many plants respond to slight increases in solar output (absorbing more enegy, and resulting much higher crops yeilds, noted by early economists). Plants also respond to higher concentrations of CO2 by darkening and absorbing more energy as well.

Also of interest, this post by Lubos Motl links to a paper by Stephen Schwartz that shows that climate sensitivity is likely to be about 1C for a doubleing of CO2. The analysis shows that lags in temperature increase following GHG increases are highly unlikely to excede 4-6 years.

Aside, I think the 5 year smoothing of the data that is done also blurs things, especially for the most recent data (I think the 1998 spike in heat may make recent temps look higher than they are). It should also be noted that all of the heat that was absorbed in 1998 quickly dissipated, this doesn't exactly support a strong greenhouse effect (thougth it doesn't disprove it). The smoothing and curve fitting also present make the climate look far more stable than we can be certain of. For the longer historical records, there are few data sets, the error bars are huge, the data points are really 100+yr. The curves are a bit misleading, we really don't know how much GHGs and temperatures may have fluctuated over short time spans.

[Being that the greenhouse effect is dependent on the retention of heat, I think a more proper analysis would be to look at the raw data and plot the trend in the low points in temperature fluctuations.]

At Jim: If you click the "more" link and read the updates, you will see a truncated list of specifics. One is that there is not good evedince of any significant increase in water vaper, but there does seem to be a speeding of the water cycle which would result in significant cooling. Just for one.

Daublin writes:

I second Kevin's response. The question is not the greenhouse effect. The question is how you get from the 1-degree greenhouse effect to a 5-degree or more scenario.

If the greenhouse effect is all that is involved, then CO2-control responses would be insane. The CO2-control responses are trying to hold us steady at a concentration of 600-1000 ppm, but at such a level the greenhouse effect of the CO2 is already mostly maximized. 1000ppm versus 2000ppm will both cause a 1 degree rise.

Thus, the positive feedbacks are critical to the case for control CO2 emissions.

Daublin writes:

Okay, I have read through the whole link now. It is a good thing to read for various reasons. Let me just point out one interesting thing: this article's worst case assumption is a 3 degree rise. Some of the people they quote say that a 2-degree rise is a more plausible worst case, and the article agrees that 2 degrees is nothing to be afraid of. The article differs from the IPCC's 5 degree not-even-worst case predictions, but it does not explain why.

Barkley Rosser writes:

To Geoffrey: CO2 concentration has been rising exponentially (keep in mind it leaves the atmosphere slowly) for a long time, global temperature has been rising since the mid-1970s.

A rather nice simplification that fits the data is provided by Patrick J. Michaels, an actual climate scientist, now at the Cato Institute after having been more or less forced out at State Climatologist of Virginia. He used to be a full skeptic on whethe warming was happening, but is now a more moderate skeptic, taking the line that it is happening, and there is some anthropogenic input, but that the lower end of the IPCC projections are more likely.

To be more specific, he observes that the increase in global temp since the mid-70s has been approximately a straight line, which he says is the best guess going forward for at least the near term (beyond that, too many uncertainties). Where does this linear trend come from? The exponential increase in CO2 concentration combined with an approximately logarithmic relationship between CO2 concentration and temperature, as forecast by the most established climate science. Of course there are a lot of other things going on, but this is a pretty straightforward story, consistent with the both the available data and accepted science.

(BTW, I think I posted this argument earlier here, if so, apologize for being boring.)

Ben Kalafut writes:

That's the way to do it, really. Pretend, by omission, that the attribution studies, that the climate simulations, don't constitute "empirical evidence".

"We know certain things about CO2's absorption and emission spectrum under atmospheric conditions, but god forbid we put them into our model and do some math to see what the model predicts!

If you quit dismissing models out-of-hand and really thought about the structure of this problem, you'll find that they're more convincing than the papers you cited today--not that those papers don't help.

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