The Corner

Sensitivity

The Economist has got hold of part of a draft of the “fifth assessment” that is shortly due from the IPCC (the Intergovernmental Panel on Climate Change) and notices that it implies that the climate’s sensitivity to CO2 emissions may be somewhat less than had previously been thought.

Properly enough, the magazine throws in some substantial caveats:

The table comes from a draft version of the report, and could thus change. It was put together by the IPCC working group on mitigating climate change, rather than the group looking at physical sciences. It derives from a relatively simple model of the climate, rather than the big complex ones usually used by the IPCC. And the literature to back it up has not yet been published.

To be clear, The Economist is not leaping off the anthropogenic-global-warming bandwagon, but it is suggesting (not for the first time) that the planet may have more room to maneuver than had previously been thought:

[O]ver the past year, several other papers have suggested that views on climate sensitivity are changing. Both the 2007 IPCC report and a previous draft of the new assessment reflected earlier views on the matter by saying that the standard measure of climate sensitivity (the likely rise in equilibrium temperature in response to a doubling of CO2 concentration) was between 2°C and 4.5°C, with 3°C the most probable figure. In the new draft, the lower end of the range has been reduced to 1.5°C and the “most likely” figure has been scrapped. That seems to reflect a growing sense that climate sensitivity may have been overestimated in the past and that the science is too uncertain to justify a single estimate of future rises.

If this does turn out to be the case, it would have significant implications for policy. Many countries’ climate policies are guided by the IPCC’s findings. They are usually based on the idea (deriving in part from the IPCC) that global temperatures must not be allowed to increase by more than 2°C above pre-industrial levels, and that in order to ensure this CO2 concentrations should not rise above 450 ppm. The draft table casts doubt on how solid the link really is between 450 ppm and a 2°C rise. It remains to be seen whether governments conclude from this that it is safe to let CO2 concentrations climb even further, or whether (as some will doubtless argue) a 2°C rise was too much anyway and it is now possible to aim for less.

Interesting, but in some ways I was even more interested to read this response to The Economist’s piece over at Skeptical Science (“getting skeptical about global warming skepticism”). Its author argues that The Economist has misinterpreted the data, and goes on to explain why (take a look and judge the merits for yourselves). To argue that The Economist has “screwed up” is, of course, fine, but the writer for Skeptical Science goes further, describing what the magazine has written as “irresponsible,” an adjective that, in this highly politicized context, strikes me as being just the teeniest bit authoritarian. The writer then draws on an earlier incident to say that “you shouldn’t report on draft documents that are subject to change,” a comment that not only comes across as a little bossy, but overlooks the fact that the way in which IPCC reports have “evolved” has been a matter of considerable interest (Climategate and so on) for some time.

In any event, since when can you have too much discussion of the science? Trying to shoot down the arguments made by The Economist is one thing, but seeming to suggest that they should never have been made is something else altogether, and it reveals an attitude that is, unfortunately, all too common amongst a good number of those most committed to current AGW orthodoxy.

In The Age of Global Warming (note to editors: the review is almost done) Rupert Darwall notes this:

For [Karl] Popper [Yes, him again], intolerance and lack of respect for dissenting opinions were antithetical to the precepts of an open society. Dissent is also linked to the success of science in expanding scientific knowledge because criticism is the engine of the growth of knowledge . . . The growth of scientific knowledge came not from the accumulation of observations, Popper argued, but from the repeated overthrow of scientific theories and their replacement by better or more satisfactory ones.

Creative destruction, you might call it, although I believe the term has been taken.

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