USENET has an extremely deserved reputation as a refuge for nasty, cranky, crazy and porn, still there are prescient voices of wisdom and good information to be had. Eli would like to point out that the recently "discovered" idea that one has to take into account the asymmetry of possible outcomes from climate change is an old one to those who used to practice on such groups as sci.environment, and not a recent discover of Weitzman, newly taken up by Anthoff, Tol, Yohe and others. True this offers them an elegant out so they don't have to say Stern was right and we were wrong. Michael Tobis, yes, that guy, put it best:
My beliefs regarding the costs and benefits of:
1) Global mean temperature is a mere proxy measure of change, and very large climate shifts with very small global mean temperature change are admissible, while the opposite case is meaningless. So focusing on mean temperature shifts already has a neutral to overly optimistic outcome.
2) As everyone is constantly pointing out, current understanding of climate as embodied in dynamic climate models is relatively crude. The result is indeed that the models are unreliable. However, contrary to what I have seen anywhere in the popular press, this means that the models are biased to produce results similar to contemporary climate using contemporary boundary conditions. They therefore tend to be undersensitive to perturbations. Again, this implies that the median modeling result may be an underestimate.
Another problem is that the real world has more degrees of freedom than any model, so modes not accounted for in models may be excited in reality. Again this causes model projections to be conservative regarding change estimates.
3) As has been stated recently, human institutions are built around prevailing conditions. Therefore any change occurring more rapidly than the optimum replacement time for these institutions has considerable costs. The example of building near sea level is the most obvious, though here it seems that the relevant time constants are long (several centuries rather than several decades). Regarding climate change itself, the dominant time constants are those of the atmosphere and the upper ocean, respectively a month or so (effectively instantaneous) and roughly 20 to 30 years. So the non-sea-level related changes are not imponderably distant in time.
4) It is clear enough that a change of 20 C would be cataclysmic, whether that change is a warming or a cooling. It is also clear enough that a change of 0.2 C is of little consequence, and may be on net beneficial. There is no reason to believe that this function is linear. The contemplated changes (~2 C) are large enough that we can not have total confidence that the impacts will not be catastrophic.
5) There is no plausible argument that any particular climate change will have a beneficial impact comparable to the worst plausible case negative impact.
6) The risk-weighted cost of unrestrained anthropogenic perturbation must therefore be dominated by the fact that the plausible worst cases have more cost than the plausible best cases have benefit.
7) I believe that resources should be dedicated not only to best models of current climate but to explorations of plausible worst case scenarios, precisely because these dominate the risk-weighted cost. This is the main way in which science can directly relate to the rational mitigation response strategy, if there's a sensible way to do it. I have heard of no efforts in this direction. Climate science as currently performed can provide much more of use to adaptation strategies, which are local, than to mitigation strategies, which are global.
8) The magnitude of the best estimate temperatureto anthropogenic inputs is not likely to change unless new global scale processes become active. The current global temperature sensitivity is well understood barring such changes, despite what you read in the press.
Point 2 above implies that at longer time scales, model changes are more likely to be underestimates than overestimates. For the foreseeable future the global picture is not likely to change.
9) Most of our knowledge points to the changes being larger than appear in nature. Meanwhile our ignorance prevents us from knowing at what level these changes become intolerable. The potential risk is enormous. The potential benefit is modest.
10) There is no *guarantee* that the climate shift will not be advantageous. There are reasons to suspect otherwise. There are *strong* reasons to suspect that *sufficiently rapid* changes are disadvantageous and it's perfectly obvious that *sufficiently large* changes are disadvantageous. The most important point, though, is that plausible negative outcomes have much larger costs than plausible positive outcomes have benefits.
11) The correct level and strategy of response are difficult to establish, and intelligent and vigorous discussion is warranted. Delay is not. The time constants of the human system that causes the perturbation and the time constants of the climate response don't offer any zone of comfort. Indeed it is difficult to eliminate the prospect of very serious consequences of the perturbation that has already taken place or will unavoidably occur before effective policies can be implemented.
12) The most likely time for catastrophic consequences not involving sea level change is in the next century. This is neither in the typical political time frame nor so far in the future that the matter can be treated as merely theoretical.
OK, this is sort of cheating, but as far as Eli can see Michael has not put this up on Only in it for the Gold and it needs to be repeated again and again. We can negotiate if he wants to put it up on