Arnold Kling  

Empiricism and Global Warming

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I am reading Frederick Crews' The Follies of the Wise, which collects essays he has written over the years attacking creationists, UFO believers, Freudians, and others. The common thread is his unrelenting empiricism.

Greg Mankiw exposed my skepticism on Global Warming to his audience, and got a couple of predictable comments.

One interesting comment points to an article on wagers made by scientists on global warming. Read the whole article.

One person wrote,


Questioning the validity of scientists on global warming is like questioning the validity of economists on the economy.

I would say that it is more like questioning the validity of creation scientists on creation science. You could argue that Crews, a literature professor, has no right to criticize the people that he does. But he argues as an empiricist. So do I.

Another commenter chides Mankiw,


Review the scientific literature. Don't be lazy. Inform yourself. This is too important an issue for smart and influential people like you to remain ignorant about.

I felt the same way, which is why I looked into the literature, and why I came out the way that I did. Readers who have not been following my thought process can browse the energy-environment archive.

Basically, I believe that the best evidence for global warming is global warming. That is, the rise in observed temperatures is the most important data.

That rise began around 1900, and amounted to about 0.3 degrees centigrade by 1940. Temperatures leveled off until 1980, and since then they are up 0.4 degrees centigrade.

Much, much more of the human activity that would cause global warming has occurred in the last 20 years than took place between 1900 and 1940. Also, much, much more of the greenhouse gas layer on earth consists of either water vapor or pre-industrial levels of carbon dioxide.

Thus, the link between human activity and global warming depends not on simple, obvious relationships in the data. It depends entirely on climate models of how these tiny (relative to the overall volume of greenhouse gases) human activities produce "feedback loops" on the rest. They are models of how much less than one percent of a phenomenon affects the entire phenomenon. They are much more faith-based than empirical.

It is possible that the models underestimate human-caused global warming. However, I believe that this is far less likely than that they over-estimate the human causal factor.

I believe that average temperatures have been rising. I have no reason to believe that they will stop rising. However, the most sensible position an empiricist can take is that human activity is not going to make much difference to global warming, one way or the other.


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COMMENTS (7 to date)
bing writes:

Arnold, as someone who is trained in the sciences I share your skepticism around global warming. There are a number of issues that must be confronted in an open manner.

First, are we not defining the problem in operational terms. That is, do we not define global warming as global warming. From earth-based temperature readings we can infer that the temperature has risen in the last 100 years about 1 degree. However, the facts also show that the temperature has also fallen about half a degree over the past forty years when we use satellite-based measurements (Yes, the satellite measures record atmospheric temperatures versus earth based measures.). Net, while we have basis for inferring that the temperature is increasing we cannot rule out that we may have systematic measurement error associated with how we measure.

Second, we have the issue as to how to define what the Earth’s normal temperature should be. Even if we could agree that the temperature has increased, we cannot seem to come to grips with whether is it outside a normal range for Earth. Using history as a guide we cannot conclude that the temperature is moving outside of historical norms. Temperatures are well within historical and pre-man (I use man and should say white man given they are the culprits) levels. Thus, here again it is hard to get worried that we have a major problem.

Third, there is no clear theory on global climate change. That is, we have no clear causal mechanisms in place that pass a battery of tests. All the theories pass a few simple tests. None withstand the rigor we employ in other areas or science. The models to date are driven by a limited subset of all the known variables contributing to global climate change. One can argue that all models are subsets which is more than fair. However, the omission of key variables such as solar activity that attenuate the amount of solar radiation absorbed by the Earth is material. The failure to capture the Iris effect is another material omission. A further problem confronting a number of the larger models is that they are terrible at explaining historical data patterns. This is a material defect and should lead investigators to sparingly infer anything from such models.

Forth, what is the consequence of global warming? Here we have no clear answer. We have some hypotheses that suggest that we will have increased rain fall others less rain fall and yet others arguing both. We then have those hypothesizing rising sea levels and coastal flooding. There are yet others hypothesizing for more extreme weather. I do not want to forget those who claim increased hurricane activity ( My peers are very skeptical of this claim.). We have another group forwarding improved growing conditions. Global warming alarmists do agree on one conclusion that we should be very concerned. I for one conclude that we should continue our study.

Fifth, we have no real use of benefit/cost analysis to frame the discussion of alternatives and their potential outcomes. It is not surprising given that we do not really understand the causal mechanism nor the consequences. We just have a belief that global warming is “bad” and we must stop its. This is a terrible problem.

Sixth, and more serious than the others issues I have is that anyone who questions the “facts” is attacked. This is really sad and serious. I have colleagues who are afraid to express skepticism publicly for fear of retribution. This is a new development in the sciences. If not challenged it will destroy our Universities.


In summary, I think your skepticism is well founded and fact-based. In addition, I applaud your willingness to honestly and in a fact-based manner challenge the self-righteous. Good job!

Steve writes:

Global warming is either significantly the result of human activity or it isn't. If it is, then human activities such as aquaculture, which would produce a carbon sink by seeding the oceans (and producing private rights to the high seas in the process) would resolve the problem. If it isn't, then curbing human activities will not solve the problem.

Either way, Kyoto is a bad idea. It either robs people of weath and does nothing positive, or it robs people of the wealth to do something positive.

Jon writes:

Much of the value of the scientific enterprise is to make predictions about an uncertain future. If all science just stopped at describing the results of a benchtop experiment, it would not be of much use. Engineers use this science and quickly learn the limits of science when they scale things up to a useful size. Unfortunately in this case, the useful size is the whole planet. If we screw up, we don't get to build another prototype.

There actually is a lot of testable science underlying global warming. We can measure and test the absorption spectra of various gas, such as CO2 and methane.We can measure the reflectivity and absorption spectra of various materials in the planet. All of this is testable. The only thing things that are much more difficult to test are: 1) Are there feedback mechanisms (possible increase in cloudiness or plant activity), other human activities (i.e. dust producing) or non-anthromorphic (future volcanic eruptions) which will counter the greenhouse effect, and 2) precisely how various regions will be affected by global warming.

The real religion here is by libertarian economists--they have a set of facts that implies a need for something that goes against their belief. That something is government intervention into the economy.

Roger M writes:

It's legit to argue that nonspecialists in a field exercise a little humility when criticizing specialists. Nonspecialists make a lot of mistakes that even amateurs wouldn't. I see this a lot when scientists or economists discuss philosphy. So climatologists should get more respect than economists when discussing global warming.

However, climatologists can't expect us to treat them like high priests. They should be able to explain their positions in ways that educated people, at least, can understand and evaluate. If they believe that humans are causing global warming, they should be ble to present the evidence in such a way that economists and other intelligent people can examine their evidence and agree or disagree with them. So far, the evidence that they have offered, to some degree their methodolgy, and their conclusions, are suspect. But they insist that we accept their conclusions because they are the climatologists and we're not.

Just as no one should accept the word of an economist just because he's an economist, we can't accept the word of scientists just because they're scientists. Those scientists who believe in human-caused global warming are going to have to do a better job presenting the evidence for their conclusions and defending their methodology, and less effort on appealing to their priestly authority.

dearieme writes:

"A further problem confronting a number of the larger models is that they are terrible at explaining historical data patterns": in which case we should bin them as worthless. The have failed the only meaningful test of such models.

Rick writes:

So climatologists should get more respect than economists when discussing global warming.

By extention, economists should get more respect than climatologists when discussing climate change policy.

rmark writes:

http://www.clearlight.com/~mhieb/WVFossils/greenhouse_data.html

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