Coyote Blog has a bit I missed on the latest IPCC report (2007) on climate change.
It is silly to argue whether CO2 in the atmosphere can cause global warming: It clearly does. The issue is not "if" but "how much". The warming from man's CO2 might be 8 degrees in a century, as Al Gore might argue, in which case man's CO2 would be incredibly disruptive. Or it might cause just a few tenths of a degree of warming, which might be unnoticeable within the noise of natural climate variation.Well Coyote has a nice chart. It shows that IPCC estimates for the amount of "heating" CO2 does to the global climate system has been declining with each report. And yet the warnings get more dire with each report. How can that be?
Interestingly, the key to understanding this issue of the amount of warming does not actually lie in greenhouse gas theory. Most scientists, skeptics and alarmists alike, peg the warming directly from CO2 at between 0.3 and 1.0 degrees Celsius for a doubling in CO2 levels (this notion of how much temperatures would increase for a doubling of CO2 levels is called climate sensitivity). If this greenhouse gas warming was the only phenomenon at work, we would expect man-made warming over the next century even using the most dire assumptions to be less than 1C, or about the same amount we have seen (non-catastrophically) over the last century. Warming forecasts of this magnitude would not in any way, shape, or form justify the draconian economic impacts of many current government carbon reduction proposals.
The key, as I have written before (and here), lies not in greenhouse gas theory itself but in the theory that the earth's climate is dominated by positive feedback. This theory hypothesizes that small changes in temperature from greenhouse gas increases would be multiplied 3,4,5 times or more by positive feedback effects, from changes in atmospheric water vapor to changing surface albedo.Well isn't that interesting. Climate catastrophe is based on positive feedback. And yet...
Let me emphasize again: The catastrophe results not from greenhouse gas theory, but from the theory of extreme climactic positive feedback. In a large sense, all the debate in the media is about the wrong thing! When was the last time you saw the words "positive feedback" in a media article about climate?
So how confident are we in these feedback effects? Well, it turns out we are not even sure of the sign! As Monckton writes:So the most important factor in the greenhouse catastrophe scenario is not understood. No wonder why it isn't discussed.The feedback factor f accounts for at least two-thirds of all radiative forcing in IPCC (2007); yet it is not expressly quantified, and no “Level Of Scientific Understanding” is assigned either to f or to the two variables b and κ upon which it is dependent....Given the importance of feedback to their forecasts, the treatment in the latest IPCC report of feedback borders on the criminal. I have read the relevant sections and it is nearly impossible to find any kind of discussion of these issues. A cynical mind might describe the thousands of pages of the IPCC report as the magician grabbing your attention with his left hand to hide what is in his right hand. And what is being hidden is that ... there is nothing there! Feedback is the pivotal point on which the whole discussion of drastic carbon abatement should turn and there is nothing there.
Indeed, in IPCC (2007) the stated values for the feedbacks that account for more than two-thirds of humankind’s imagined effect on global temperatures are taken from a single paper. The value of the coefficient z in the CO2 forcing equation likewise depends on only one paper. The implicit value of the crucial parameter κ depends upon only two papers, one of which had been written by a lead author of the chapter in question, and neither of which provides any theoretical or empirical justification for the IPCC’s chosen value. The notion that the IPCC has drawn on thousands of published, peer-reviewed papers to support its central estimates for the variables from which climate sensitivity is calculated is not supported by the evidence.