by Judith Curry
The recent controversies surrounding Kevin Trenberth deserve its own thread.
First, we have his preprint for his talk on Climategate for the forthcoming annual meeting of the American Meteorological Society can be found here. This is being discussed at WUWT and Lubos Motl. It will be interesting to see how the AMS responds to this (the AMS has many skeptics among its membership). Well, everyone is entitled to their opinion, but as a smart move in the politics of expertise, well this statement can’t rank very high, IMO.
Steve McIntyre chimes in with an historical perspective on Trenberth’s activities in the climate debate.
On the science front, Trenberth has stated in an article posted on Yahoo News about the Brisbane floods that “So it is easy to argue that 1 degree Celsius sea surface temperature anomalies gives 10 to 15 percent increase in rainfall.” This statement about the Brisbane floods follows his previous statements attributing the Pakistan floods and Russian heat wave to global warming.
He makes the argument in the AMS preprint that:
Given that global warming is “unequivocal”, to quote the 2007 IPCC report, the null hypothesis should now be reversed, thereby placing the burden of proof on showing that there is no human influence. Such a null hypothesis is trickier because one has to hypothesize something specific, such as “precipitation has increased by 5%” and then prove that it hasn’t. Because of large natural variability, the first approach results in an outcome suggesting that it is appropriate to conclude that there is no increase in precipitation by human influences, although the correct interpretation is that there is simply not enough evidence (not a long enough time series). However, the second approach also concludes that one cannot say there is not a 5% increase in precipitation. Given that global warming is happening and is pervasive, the first approach should no longer be used. As a whole the community is making too many type II errors.
So we frequently hear that “while this event is consistent with what we expect from climate change, no single event can be attributed to human induced global warming”. Such murky statements should be abolished. On the contrary, the odds have changed to make certain kinds of events more likely. For precipitation, the pervasive increase in water vapor changes precipitation events with no doubt whatsoever. Yes, all events! Even if temperatures or sea surface temperatures are below normal, they are still higher than they would have been, and so too is the atmospheric water vapor amount and thus the moisture available for storms.
Well, burning fossil fuels and other anthropogenic activities have undoubtedly changed the climate and even weather patterns, the butterfly flapping its wings in Brazil, and all that. Maybe the Brisbane floods would have been less severe without humans on the planet, but maybe the flood would be more severe, there is just no way to know about an individual weather system and it is a pointless question to ask. The kinds of statistical analyses of climate model simulations to come up with such statistics arent convincing IMO (the attribution of extreme events will be the topic of a future post.) The reason reporters ask this kind of question can probably be traced back to Trenberth’s statements in 2005 attributing 7% of the intensity of Hurricane Katrina to global warming, and that 7% of the intensity was just enough to breach the levees (or something to that effect.)
So back to the politics of expertise, which is the theme of this series. The skeptics are certainly having a go at Trenberth. Reactions from lukewarmers and IPCC supporters? Do you think Trenberth is helping or hindering public education and developing political support for the climate change issue?
Note: I hope to have time this weekend to do a technical post, will try to address the 10-15% increase in precip issue raised by Trenberth, or the issue of attribution of extreme events.
Moderation note: No rude words or personal insults. Criticize the statements or the strategy, but no personal insults, I will be deleting insulting statements that do not make substantive points.