The Volokh Conspiracy
Mostly law professors | Sometimes contrarian | Often libertarian | Always independent
When it comes to climate change, there is an amazing confluence of policy preferences and scientific assessments. Those who generally favor aggressive regulatory interventions to address environmental concerns are convinced global warming is a serious (if not catastrophic) environmental concern, while those who generally oppose governmental interventions in the marketplace are skeptical of mainstream climate science. Each side of the policy debate has adopted a view of the science that confirms—or at least conforms with—its policy preferences.
It would be nice if reality lined up just so, but that's not the world in which we live. As I wrote in 2008:
Given my strong libertarian leanings, it would certainly be ideologically convenient if the evidence for a human contribution to climate change were less strong. Alas, I believe the preponderance of evidence strongly supports the claim that anthropogenic emissions are having an effect on the global climate, and that effect will increase as greenhouse gases accumulate in the atmosphere. While I reject most apocalyptic scenarios as unfounded or unduly speculative, I am convinced that the human contribution to climate change will cause or exacerbate significant problems in at least some parts of the world. For instance, even a relatively modest warming over the coming decades is very likely to have a meaningful effect on the timing and distribution of precipitation and evaporation rates, which will, in turn, have a substantial impact on freshwater supplies. That we do not know with any precision the when, where, and how much does not change the fact that we are quite certain that such changes will occur.
Over at Reason, Ronald Bailey points out that the cumulative evidence in support of the basic proposition that human emissions of greenhouse gases are contributing to a gradual warming of the atmosphere is substantial—even if it is inconvenient for a libertarian to admit. He reaches this conclusion without relying upon the conclusions drawn by computer models or contested studies, such as Michael Mann's infamous "Hockey Stick." That is, even ignoring such studies, the evidence is quite strong. Writes Bailey:
It might be that it … just so happens that natural climate variability has boosted global temperatures and the trends discussed above are occurring coincidentally at the same time the concentrations of carbon dioxide are 30 percent above their highest levels in the past 800,000 years. Correlation does not imply causation. The data cited (and uncited) do not prove beyond a reasonable doubt that man-made climate change is real. However, in my best judgment the preponderance of the evidence suggests that the greenhouse gases produced by humanity are warming the climate and that it could be a significant issue later in this century.
As I've written elsewhere, it's long past time that self-professed libertarians and others on the political right consider climate change to be a serious problem. (See also here.) The Niskanen Center's Jerry Taylor makes a similar point here. Alas, many libertarians and conservatives reject evidence of humanity' effect on the global climate system for fear such evidence will be used to justify climate policies libertarians and conservatives rightly dislike.
The right's general posture on climate science leads Bailey to quote F.A. Hayek's seminal essay, "Why I Am Not a Conservative":
Personally, I find that the most objectionable feature of the conservative attitude is its propensity to reject well-substantiated new knowledge because it dislikes some of the consequences which seem to follow from it-or, to put it bluntly, its obscurantism. I will not deny that scientists as much as others are given to fads and fashions and that we have much reason to be cautious in accepting the conclusions that they draw from their latest theories. But the reasons for our reluctance must be rational and must be kept separate from our regret that the new theories upset our cherished beliefs.
To restate: The existence of man-made warming does not mandate any particular policies. So back to the headline question: If generally rising temperatures, decreasing diurnal temperature differences, melting glacial and sea ice, smaller snow extent, stronger rainstorms, and warming oceans are not enough to persuade you that man-made climate is occurring, what evidence would be?
It is a question worth answering.