The general strategy of conservatives and some business interests has been to try to increase uncertainty about global warming in order to defeat climate change legislation. And if recent polls are accurate, the public has been listening to their arguments.
But they should not. The argument from uncertainty in fact strengthens rather than weakens the case for strong action on climate change.
Let’s assume, for the sake of the argument, that global warming predictions are as uncertain as conservatives claim.
The IPCC predicted an increase in global mean temperature of roughly 3.5 degrees Celsius as the most likely scenario. At this level of warming, if left unchecked, the National Resource Defense Council estimates that this would cause a loss of 3.6% of GDP by 2100 in the U.S. with more significant losses elsewhere in the world. And of course this does not include non-economic effects which may be considerable.
Given the uncertainties of climate modeling, and the inherent difficulty of predicting the behavior of complex chaotic systems, there is some possibility that conservatives are correct. Perhaps there will be no warming. But uncertainty does not apply in only one direction. A margin of error sufficiently large such that a prediction of 3.5 degrees C could yield a possibility of no warming entails an equal possibility that global warming could be as bad as a 7 degree increase in global mean temperature. In other words, in the absence of auxiliary hypothesis that would skew the distribution, the margin of error is equal on both sides of the prediction. Assuming a confidence level equivalent to no warming on the left side of the distribution, the possibility of catastrophic warming is as likely as no warming. [h/t to John Quiggin at Crooked Timber for making this point.]
And in fact there are a variety of auxiliary hypothesis that lead to the conclusion that the IPCC prediction is too low.
The belief that uncertainty must mean that things can only be less bad than predicted is purely wishful thinking, not science.
This has profound implications for policy proposals. When considering the expected consequences of proposals to mitigate global warming, we must also consider the expected consequences of doing nothing which must include the costs of doing nothing if the worst case scenario develops. An increase in global mean temperature of 7 degrees C would according to some estimates produce massive ecosystem collapse and the deaths of billions of people.
Thus, taking account of uncertainty, the expected costs of doing nothing overwhelm any reasonable account of the expected costs of mitigating climate change, which as Paul Krugman argues will be minor.
There is utterly no case to be made for inaction and a strong case to be made for developing mechanisms to quickly ratchet up reductions in emissions if, as we reduce the uncertainty of the science, we find catastrophic warming becoming more likely.
There is lots of uncertainty in the science and economics of global warming but that uncertainty is an argument in favor of action now.
