Bryan Caplan  

Global Warming: The Experts Speak

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Yes, I'm an elitist: When laymen and experts disagree, my presumption is that the laymen are wrong and the experts are right. Whether the subject is economics, toxicology, or global warming, that's my starting point (though not always my ending point). With global warming much in the news, I've been curious about the experts consensus - and I've gotten a lot of value out of Bray and Storch, The Perspectives of Climate Scientists on Global Climate Change.

My overall impression: Given skeptics' weak interest in taking reasonable bets, I'm surprised by the moderation of scientific opinion. The experts almost always lean in the way Al Gore says they would, but they rarely lean strongly. Even on "We can say for certain that global warming is a process already underway," the median answer on a 1-7 scale (1="strongly agree"; 7="strongly disagree") is only 3.

How reliable is this survey? Well, on the one hand, climate change skeptics like it. But on the other hand, the authors aren't happy with how skeptics are using their survey. Personally, I wish the survey measured the political views of the respondents, allowing us to test for ideological bias - but it doesn't look like it did. Alas - this is definitely an issue where I'd like a nonpartisan perspective.

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COMMENTS (16 to date)
James A. Donald writes:

I recommend

This guy is a real scientist, who specializes in auditing global warming papers - mostly checking whether reported results actually represent the data.

And he has found a huge number of examples of unscientific practice that is close to fraud, or arguably fraud.

As a result of Steve's work, the case for Global Warming now resembles the case of Uri Geller's psychic powers. Maybe Uri Geller really can bend spoons with his mind. He has been caught bending them with pliers a few times, but what about all the times he was not caught

That does not prove that global warming is fictitious - but it does prove that the case for Global Warming has been made by means that were grossly improper.

Dr. T writes:

I'm a medical doctor/scientist, not a climatologist, but I actually read the full IPCC report on climate. That report contained more garbage than a large city's landfill. Here's my take on this issue:

Both ocean and land temperature measurements used to track year-to-year temperatures are so inaccurate that the readings are nearly worthless. Haven't climate people heard of standardized thermometers?

No one really knows how to combine land, ocean, and atmospheric temperature readings to get a true global temperature.

Sea level measurements at different points around the globe are even less accurate than temperature measurements.

Satellite studies of the arctic and antarctic produce unreliable data about ice thickness.

Global temperature models (used to predict future temperatures) range from bad to awful. The IPCC created a meta-model by combining 24 individual models. The meta-model was better than any individual model (which isn't saying much). The meta-model was tested by putting in many years of real data and then predicting 1991-2000 temperatures. The IPCC bragged that 95% of the modeled zones had annual mean temperatures within 2 degrees centigrade of the real values. What they failed to publicize is that most of the areas where the meta-model failed were near the poles, and that the meta-model gave arctic and antarctic temperature predictions that were 6 degrees warmer than the real values. Even though the IPCC knew its meta-model did poorly near the poles, and even though the IPCC knew that the polar regions are major factors in global climate, it still used the meta-model to predict future climate. Naturally, the predictions showed massive melting of the ice caps, rapidly rising sea levels, and disastrous flooding of coastal regions.

The claim that increased atmospheric CO2 (supposedly from burning fossil fuels) produces a greenhouse effect that contributes to global warming is not supported by the data. Instead, the data indicates that warmer temperatures (caused by increases in solar output) result in CO2 being released from water (the same way that warm soda loses CO2). The other fact that global warming scare mongers forget to mention is that even if the greenhouse effect was real (it isn't, because the world is not a closed system sealed under glass), CO2 contributes little. The atmosphere does contain 'greenhouse gases.' The predominate 'greenhouse gas,' accounting for 95% of the greenhouse effect, is water vapor.

I could continue ranting about the pseudoscience behind the 'man is causing global warming that will destroy the world' movement, but this is the wrong forum.

General Specific writes:

Do ensure you report all the results from their survey (selection bias?):

From Wiki: "The same survey indicates a 72% to 20% endorsement of the IPCC reports as accurate, and a 15% to 80% rejection of the thesis that "there is enough uncertainty about the phenomenon of global warming that there is no need for immediate policy decisions.""

Therefore, what Bray and Storch tell us is that the experts significantly endorse the IPCC and significantly believe that something should be done.

Also note that their analysis was performed using an internet survey that was subject to abuse.

Jeffrey Rae writes:

I am surprised that a Hayekian would generally side with expert over lay opinion. Surely it has to depend on the precise question that is being posed and on who hold the information that is relevant to the answer.

Just because we are economists, we economists are not better than the rest of the population at forecasting the future course of the economy. If we were, I would expect that most of us would be fabulously rich. As far as I can see we are not, unfortunate as that undoubtedly is!

I can see no reason why climate modelers would be able to predict the future course of the global climate over the next 100-200 years any better than macroeconomic modelers could predict the course of the global economy over the same period.

I believe the same holds true for other professions in areas of their professional competence: lawyers forecasting court decisions in cases on which they are not represented, for example.

As for the IPCC Report I would make a the following observations. (1) the Summary for Policymakers was NOT written by climate scientists but by government bureaucrats. (2) the extremely large amounts of government funding for climate research is likely to affect what individual scientists are willing to say on the subject. (3) there is evidence of a 'party line' being enforced on independently minded scientists by threats to their employment, reputation or research funding.

General Specific writes:

"(1) the Summary for Policymakers was NOT written by climate scientists but by government bureaucrats."

From what I understand, the report was watered down by the political arm to make it more politically palatable--read economically palatable--not the opposite.

"I can see no reason why climate modelers would be able to predict the future course of the global climate over the next 100-200 years any better than macroeconomic modelers could predict the course of the global economy over the same period."

All depends on what you're predicting. If you're predicting the path of a space craft, rely on experts. For more complex systems, the data can only say so much. Was a time one couldn't predict even a space craft's position. We'll sooner predict climates than economies. Humans are more complicated.

In general, I find that people rely on experts when the experts agree with them. On subjects like global warming and peak oil, the experts are speaking pretty clearly but it's not politically or economically palatable to do anything--or even accept the science.

So when that happens, the people who rely on experts become experts on how experts shouldn't be used.

Rich Berger writes:

Dr. T-

Where did you get the report? How much does it cost?

broadly focused writes:

A big problem with the mathematical and physical models for climate prediction is that well accepted and verified models do not exist for the complete system. As Arnold pointed out, Freeman Dyson put it very well

The models solve the equations of fluid dynamics, and they do a very good job of describing the fluid motions of the atmosphere and the oceans. They do a very poor job of describing the clouds, the dust, the chemistry and the biology of fields and farms and forests. They do not begin to describe the real world that we live in. The real world is muddy and messy and full of things that we do not yet understand. It is much easier for a scientist to sit in an air-conditioned building and run computer models, than to put on winter clothes and measure what is really happening outside in the swamps and the clouds. That is why the climate model experts end up believing their own models.

There is no doubt that parts of the world are getting warmer, but the warming is not global. I am not saying that the warming does not cause problems. Obviously it does. Obviously we should be trying to understand it better. I am saying that the problems are grossly exaggerated. They take away money and attention from other problems that are more urgent and more important, such as poverty and infectious disease and public education and public health, and the preservation of living creatures on land and in the oceans, not to mention easy problems such as the timely construction of adequate dikes around the city of New Orleans.

Well put.

aaron writes:

Rich, you can download it in parts from IPCC:

Here's the Working Group 1 report.

Acad Ronin writes:

Kesten Green and J. Scott Armstrong have a paper forthcoming in Energy and Environment arguing that with respect to forecasting what we have is a large number of forecasts by scientists but no scientific forecasts. That is, they argue that the forecasts we have violate basic rules and guidelines for good forecasting practice, and hence are of no value. To see the paper go to:

A second point one might make is that Philipp Tetlock's recent book, " Expert Political Judgment: How good is it? How can we know?", is pretty scathing re the value of forecasts by experts. Tetlock finds that experts beat informed amateurs by a little, but both are pretty poor. For a review of Tetlock published in the International Journal of Forecasting, see:

broadly focused writes:

A comment on expert predictions . . .

Also from Dyson's recent book, "A Many-Colored Glass", he makes reference to the ability of 'experts' to predict the future. A classic example is provided by John Von Neumann -- a true genius of physics, mathematics, and computing -- who, when asked how many computers the nation would ultimately need, replied with something like "10". Of course he was not pretending to base this prediction on "scientific consensus" or a sophisticated simulation, it was just the opinion of one of the world's foremost experts on computing, and based on his detailed understanding of the foreseeable uses for computers. It is easy to laugh about this now, but, at the time, there was no one I would have trusted more than him on this topic.

Bob Hawkins writes:

Speaking of the IPCC AR4 WG1 report linked above, scroll down to section Parameter Choices and ‘Tuning’. Note the second requirement:

"2. The number of degrees of freedom in the tuneable parameters is less than the number of degrees of freedom in the observational constraints used in model evaluation. This is believed to be true for most GCMs... but no studies are available that formally address the question."

Think about that for a while.

As to skeptics being unwilling to bet on future warming, how is that to be measured? The surface global averages are Godless farragoes of dodgy statistical methods. The satellite MSU temperatures are pretty good, until the surface people torture them to bring them into pseudo-agreement. If someone won't bet on a fight being promoted by Don King, that may indicate he knows something about the fight game.

aaron writes:
ZAG writes:

For 10 years I conducted contract research at a large university. I can assure you that if someone gave $100K to find out if a monkey's urine is blue, there will be some researcher who will find a colony of blue urinating monkeys.

That said, science is not determined by consensus. Recall that these same "scientists" were warning of a gobal ice age in tahe 1970s.

TGGP writes:

This reminds me of your dismay that economists are too even-handed when they have an outlet to the public.

Speaking of expert predictions, what do you guys think of this on Bruce Beuno de Mesquita?

Dr. T writes:

To Rick Berger:

The (unfinished) report was free. It was the last draft before release (without the "executive summary"). You had to register on a web site and then request a password to be able to download the report and its graphs. The stated purpose of the free, though difficult, access was to get comments from scientists who were not involved in the project. The download link disappeared after the comment period was over.

The full final report is available at the IPCC web site:

The report is broken into sections, so you'll have to download numerous PDF files to get the entire report.

vicky writes:

im doing a school project and i was wondering id you could email me your thoughts on the effects global warming has on the ecosystems


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