I have just been involved in a lengthy exchange on Facebook over my criticism of the claim that warming on the scale projected by
the IPCC for 2100 can be expected to have large net negative consequences. The
response I got was that the person I was arguing with was not interested in my arguments. He does not know enough
to judge for himself whether the conclusion is true, so prefers to believe what
the experts say.
Accepting the views of experts on a question you are not competent to answer
for yourself, assuming that you can figure out who they are and what they
believe, is often a sensible policy, but one can sometimes do better. Sometimes
one can look at arguments and evaluate them not on the basis of the science but
of internal evidence, what they themselves say. Here are three examples:
The widely cited 97% figure is based mostly on Cook et. al. 2013, which is
webbed. It is often reported as the percentage of climate scientists who
believe that humans are the main cause of warming and that warming will have very
bad effects. Simply reading the article tells you that the second half is
false. The article is about causes of warming and offers no evidence on
consequences. Anyone who says it does is either ignorant or dishonest, and
other things he says can be evaluated on that basis.
If you read the article carefully you discover that the 97% figure, which is a
count of article abstracts not scientists, is the percentage of abstracts which
say or imply that humans are *a* cause
of warming (“contribute to” in the language of one example). The corresponding
figure for humans as the principal cause, which is not given in the article but
can be calculated from its webbed data, is 1.6%. That tells you that anyone who
reports the 97% figure as the number of articles holding that humans are the
main cause of warming is either ignorant or dishonest. One person who has done
so, in print, is John Cook, the lead author of the article. John Cook runs
skepticalscience.com, which is a major source for arguments for one side of the
global warming dispute, so knowing that he is willing to lie in print about his
own work is a reason not to believe things on that site without checking them. [My old blog post giving details]
One of the
economists who has been active in estimating consequences of warming is William
Nordhaus. He is, among other things, the original source for the 2° limit. A
few years ago, he published an article in the New York Review of Books attacking a Wall Street Journal piece that argued that climate was not a
catastrophic threat that required an immediate response. In it, he gave his
figure for the cost of waiting fifty years instead of taking the optimal steps
now—$4.1 trillion dollars—and commented that “Wars have been started over
smaller sums.” What he did not mention was that that sum, spread out over the
rest of the century and the entire world, came to about one twentieth of one
percent of world GNP. He was attacking the WSJ authors for an argument which
his own research, as he reported it, supported.
In a recent Facebook
exchange on the consequences of AGW for agriculture, someone linked to an EPA
piece on the subject. Reading it carefully, I noticed that the positive effects
of warming and CO2 fertilization were facts, with numbers: “The yields for some crops,
like wheat and soybeans, could increase by 30% or more under a doubling of CO2
concentrations. The yields for other crops, such as corn, exhibit a much
smaller response (less than 10% increase).” The negative effects were vague and
speculative: “some factors may counteract these potential increases in yield.
For example, if temperature exceeds a crop's optimal level or if sufficient
water and nutrients are not available, yield increases may be reduced or
reversed.” The same pattern held through the article.
careful reader might also notice that the piece referred to the negative
effects of extreme weather without any attempt to distinguish between extreme
weather that AGW made more likely (hot summers), less likely (cold winters), or
would have an uncertain effect on (droughts, floods, hurricanes). It was reasonably
clear that the article was designed to make it sound as though the effects of
AGW would be negative without offering any good reason to believe it was true.
One telling sentence: “Overall, climate change could make it more difficult to
grow crops, raise animals, and catch fish in the same ways and same places as
we have done in the past.” With most of a century to adjust, it is quite
unlikely that farmers will continue to do everything in the same ways and the
same places as in the past.
are three examples of arguments for one side of the climate controversy by a
source taken seriously by supporters of that side. Each can be evaluated on
internal evidence, what it itself says, without requiring any expert knowledge
of the subject. In each case, doing so gives you good reasons not to trust
either the source or the conclusion.
may reasonably suspect that I too am biased. But nothing I have said here
depends on your trusting me. In each case, you can look at the evidence and
evaluate it for yourself. And all of it is evidence provided by the people
whose work I am criticizing.