August 26, 2004 · Richard Posner
Good comments, and mostly supportive though some skeptical along the lines of climate models are complex, climate science is uncertain, the experts may be wrong. All true; but reading the skeptical literature, I am reminded of the debates in the 1960s over the effects of cigarette smoking on human health. The evidence for serious ill effects was already very strong, but there were skeptics, some financed by the tobacco industry, who said such things as: the evidence is statistical, the mechanism by which nicotine and tars cause changes in lung tissue, etc. is not well understood, and in short we can’t be certain that there are these effects–the implication being that we should do nothing. Similar points are made today, often by energy companies or persons in their pay, and similarly insinuating that, given uncertainty, we should do nothing.
That is a non sequitur. We rarely have the luxury of being able to act on certainties; you’d be a fool if, credibly informed that unless you had an operation to repair an aneurysm you had a 99 percent chance of dying within a week, you responded that you only act when you’re certain. In my last posting, I speculated that a 1 percent chance of criminal punishment might deter certain copyright violations, and I didn’t mean that only the irrational would be deterred.
What would be irrational would be to conclude, from the fact that a minority of scientists deride global warming fears, that we should ignore the problem. Indeed, if you look at their grounds for skepticism, you may become more alarmed about global warming rather than less so. Because what you will learn is that their skepticism is based mainly on the existence of profound uncertainties about climate, and those uncertainties cut both ways and by doing so imply added rather than diminished risk. For example, skeptics point out that in the earth’s prehistory there have been periods (one roughly 10,000 years ago) in which the concentration of carbon dioxide in the atmosphere spiked, even though cavemen didn’t drive SUVs. Yes, and if one of those non-human-induced spikes coincided with our human-induced spiking, we’ll be in real trouble.
I mentioned in passing, in the preceding posting, risk aversion. If you would rather pay $100 certain than run a 1 percent risk of a $9,999 loss, even though the expected cost of such a risk is only $99.99, then you’re risk averse (think of the $100 as an insurance premium). The greater the variance in possible outcomes, the more upset the risk averse are likely to be. The more uncertainty there is about climate, the greater the variance in possible consequences of increasing the atmospheric concentration of carbon dioxide (and of other greenhouse gases, such as methane, which is even more heat-retentive than carbon dioxide, and is being released into the atmosphere in increased quantity because of the melting of the Alaskan and Siberian permafrost–and you can see what a dangerous feedback effect is possible as more methane in the atmosphere raises surface temperatures which melts more permafrost releasing more methane…). So people who are risk averse, and that is most of us when we are facing potential disaster on the scale that global warming might inflict, will not be reassured by people who ground their global warming skepticism in nothing solider than a reminder that other things besides human activity affect climate; those other things seem as likely to exacerbate the effects of human activity as to offset them.