A Different Climate Risk

Current controversies involve a series of claims about climate known with decreasing levels of certainty. The first is that, for about the past century, global temperature has been trending up. So far as I can tell, that is well established. The second is that one cause of that increase is increased CO2 in the atmosphere due to human activity. That seems plausible as a mechanism and fits the rough pattern of what has happened. 

A third claim is that human activity is the main cause of current changes in earth's climate. The support for that is less clear. There have been two periods during the past century when the level of CO2 in the atmosphere has continued to rise for over a decade but surface temperatures have been close to constant. The first was from about 1940 to 1975; we are currently in the second. That suggests that there are causes sufficiently powerful, when they happen to be pushing in the other direction, to balance the effect on global temperature of increasing CO2 . The failure of global climate models to predict the current pause implies that such causes were not adequately taken account of in those models.

Anthropogenic global warming is a scientific theory but it is also a publicity campaign. Central to that campaign is the claim that the science is entirely settled, hence that anyone who rejects any part of the conclusion is either ignorant or corrupt. The rhetorical strategy that supports that claim, one example of which was discussed in a previous post, consists of blurring the distinctions among the claims used to support the conclusion that unless something is done to sharply reduce world output of CO2, very bad things will happen. Anyone who criticizes any link in the chain is labeled a "denier," with the implication that he denies one or both of the most solidly supported claims—that temperatures are trending up or that humans are in part responsible.

In past posts I have criticized what I regard as the weakest part of the argument, the claim that warming on the scale suggested by the IPCC models would produce large net negative effects. This post deals with a risk if the step before that is seriously wrong, if the models turn out to be much less reliable than their proponents claim.

Suppose the current pause in warming continues for another twenty years. I do not believe that the attempts to explain away the current mismatch between theory and data can be successfully maintained for that long a period. If the publicity campaign to convince the public that all scientists agree with the IPCC version of truth is successful and it then becomes clear that that version was false, it will become considerably harder to persuade the public to take seriously scientific opinion in other fields.