Café Hayek has a couple of good posts on global warming, one by Don Boudreaux, the other by Russ Roberts. I especially liked this sentence from Boudreaux: “I am not so much a skeptic of global warming. But I am indeed a skeptic of combating global warming.” A crucial distinction. The global warming debate is too often cast as a simple dichotomy: either you believe global warming is real, human-caused, hugely destructive, and cause for massive political action… or you don’t, in which case you’re a skeptic. But the debate has many more facets than that.
I’ve been trying to create a taxonomy of all the questions that ought to affect our choices about dealing with global warming. The first three questions are all best directed toward atmospheric scientists. Since I’m not one, I’m inclined to defer to the experts on these, provided I don’t think they have institutional incentives to reach certain preconceived conclusions. My perception is that the debate has revolved almost entirely around the first two questions, with some (but insufficient) emphasis on the third. But the other questions are just as relevant and will become more important as we ponder policy responses.
Existence of global warming. Is there in fact a trend of rising global temperatures? My impression is there’s a great deal of agreement on this. Call it 95%+ confidence.
Human contribution to global warming. Has human activity contributed to that trend? My impression is that support for this proposition is somewhat lower; call it 90% confidence. But I’m still not sure how much of the effect scientists think is attributable to human activity, though it’s pretty clearly less than 100%. In any case, this question may not be terribly relevant; as David Friedman points out, even if warming were entirely caused by non-human factors, we might still want to try abating it if the harms were large enough and our responses efficacious enough.
Magnitude of the warming effect. How much warming will actually occur? According to the IPCCC report, the consensus seems to be that global average temperature will rise by a couple of degrees Centigrade, with a rise in sea levels of maybe 1.5 feet (with a confidence interval around both estimates, of course).
Net harms or benefits due to warming. The key word here is net. There will assuredly be some benefits from global warming, including longer growing seasons in some areas, lower heating bills, perhaps fewer deaths from cold winters, etc. It makes absolutely no sense to focus on harms only while ignoring benefits, yet I almost never hear anyone make this point in mainstream forums. Even if the harms are larger than the benefits – as they may well be – we still have to subtract out the benefits to determine the desirability of any proposed policy responses. After all, any policy that reduces global warming will reduce its benefits as well as its harms (though not necessarily to the same extent).
Extent of decentralized response. Given that the changes wrought by global warming will occur over the course of many decades, there is every reason to believe that individuals and markets will have time to respond to changing land values and resource uses. They won’t just wake up one morning to find that Florida’s coast line has disappeared and still be looking at the same old maps. Real estate prices will adjust, people will move, land uses will change. (Unless, of course, ill-advised government insurance programs give people an incentive to stay put in flood-prone areas.) Decentralized responses mean that harms of global warming are likely to be smaller than predicted by non-economists (or lousy economists). It also means that benefits will probably be larger, as entrepreneurial efforts lead to the exploitation of new opportunities created by global warming.
Marginal impact of collective abatement efforts. Supposing we could get all the nations of the world to cooperate, how much could we expect to reduce global warming? Humans have been burning fossil fuels at a high rate for at least a century, and climate change responds to the stock of greenhouse gases in the atmosphere, not just the current flow. So to a great extent, the damage has essentially already been done. If concerted global efforts could only reduce the expected rise in sea level by a couple of inches (a number I’m pulling out of thin air, since I have no idea what the real marginal effect would be), that should reduce the perceived desirability of policy responses.
Marginal impact of unilateral abatement efforts. Realistically, we cannot get all the nations of the world to cooperate. Some rapidly developing nations like China and India will at least be reticent to adopt growth-restricting policies. Given the political reality, how much effect will unilateral efforts – or efforts adopted by only some nations – have on global warming? Although this consideration would probably reduce the perceived desirability of policy responses, it could point the other way if additional response by some nations could make up for the inaction of others.
There are many more questions than these, particularly with regard to the range of policy responses, their differing marginal efficacy, and their differing costs. So my taxonomy is incomplete, but this list is at least a start. Contributions welcome.