In the estimable Mr. Ridley’s essay published by the GWPF he provides 10 questions that he says need to be answered before he is convinced that current policy is more or less sane.
Yesterday we looked at his first test. I finished the exercise believing that we could in fact convince Mr. Ridley, given time and attention, that the question was answerable in a way that would support green policy measures to some extent. (Not everyone agrees with me–see the comment thread.)
Today we’re on to Mr. Ridley’s second question–”Despite these two contaminating factors, the temperature trend remains modest: not much more than 0.1 C per decade since 1979. So I would need persuading that water vapour will amplify CO2’s effect threefold in the future but has not done so yet. This is what the models assume despite evidence that clouds formed from water vapour are more likely to moderate than amplify any warming.”
This is the toughest question for ardent activists to answer and I have posed variations of it here on this blog–as have many other scientists, reporters and bloggers.
Because we don’t know at all what the sensitivity of the atmosphere is to a doubling of the concentrations of CO2, we cannot show Mr. Ridley a mathematical proof, a historical record or even accurate model outputs. So far we express our estimates of sensitivity as a range–the IPCC sets the parameters of this range at between 1.5C and 4.5C. If Mr. Ridley insists on one certain value we should just say frankly that we cannot persuade him and wish him well going forward.
As someone who believes that we require something in the way of a green policy oriented towards global warming (even if my ideal might differ dramatically from what’s on offer today), I would try and continue the conversation with Mr. Ridley if he were willing.
Taking the temperature since 1979 captures one period of rapid warming and one period of stasis. Averaged together they show a very tolerable level of warming if continued throughout the century. And this record certainly is not convincing evidence of a high level of sensitivity of the atmosphere.
However, given the multitude of forces that interact to move atmospheric temperatures up, down and sideways, we’ve always known that average temperatures could stall for an extended period between rises–they can even dip. As has happened during the Age of Thermometers. So I would look at more of the past and spend time trying to look into the future.
This isn’t a problem of theory–which strongly suggests that there is some level of sensitivity to rises in CO2–it’s a problem of attribution. How much of the rise from 1979 to 1998 is due to CO2, how much of the stasis since then is due to ENSO periodicity and strength, etc. We don’t know the answer to that. And if uncertainty invalidates any action for Mr. Ridley then he will end up an opponent of green policies. And again, that doesn’t make him an enemy of the human race or a bad person. He’s just an opponent in a political struggle.
Almost every scientist who has tried to calculate sensitivity of the atmosphere to CO2 has come up with a positive number for it, from Svante Arrhenius (who I think actually came up with 4 values in 4 different calculations, ranging from 2.1C to more than 6C) to James Hansen to self-proclaimed skeptic Richard Lindzen (who has variously estimated sensitivity at between 0.5C and 0.8C). Those most inclined to be activists found higher values, those most inclined to either Lukewarm or skeptical status found lower values. But that it is a positive is the norm.
I remain worried by almost any positive value and this is why. I’ve done quite a bit of number-crunching of energy consumption figures for this century and come to the dismaying conclusion that the estimates for energy consumption developed by others (particularly the U.S. Department of Energy’s Energy Information Administration) are far too low to take into account the rapid development of countries like China and India.
I have spent the last year documenting this over at my other weblog and I invite all to look through what I’ve written there–hopefully one of you will find my great mistake and I can cease worrying about this.
Until that happy day I will remain of the opinion that in 2075 the world will be using six times the energy that we used in 2010 and that most of it will be provided by burning coal. In addition to the problems of conventional pollution and black soot this will cause, it will also emit incredible volumes of CO2.
And my fear is that even with a low sensitivity, when combined with a confluence of upward movements in the other various cycles affecting our temperatures ranging from ENSO to solar cycles to even our progression through Milankovitch cycles, that there will be a pronounced effect on temperatures.
So I would say to Matt Ridley that he has identified the area of weakness that must be addressed if climate science is to provide definitive answers instead of provocative questions. I don’t have the hard answers he may require to enlist his support in efforts to contain our contributions to climate change, and I honestly don’t think anyone else does, either.
But if he is unwilling to make even a modest provision for an uncertain future, given what little we do know, that will make Mr. Ridley, much as I respect him and admire what he’s written, my political opponent in this struggle.