[youtube http://www.youtube.com/watch?v=mdoln7hGZYk&w=480]
There’s been much ado about climate sensitivity — the amount of warming we expect for a doubling of CO2 in the atmosphere — in the last month or two. A couple of recent papers, and an expected slight adjustment to the likely range in the upcoming IPCC fifth report1, has led to speculation that we might have less to worry about, or more time to get emissions cuts in place. It would be great if it were true, but it isn’t. In this excellent short video, Andrew Dessler, professor of atmospheric sciences at Texas A&M university, explains why atmospheric physics means it’s very unlikely that the climate sensitivity can be below 2ºC.
For lots of other reasons why the most likely value remains about 3ºC, see this Skeptical Science post.
- From 2ºC to 4.5ºC in AR4 to 1.5ºC to 4.5ºC in AR5, with the most likely value still around 3ºC [↩]
There is a lot going on and a lot of uncertainty about the likely outcome. 3C would be a disaster to food production and lead to mass starvation and population movement. I was just reading about the uncertainty about methane hydrates in the Arctic, http://www.theguardian.com/environment/earth-insight+world/arctic
Its not looking good.
Richard Alley spoke on climate sensitivity in the talk he gave to the recent AGU Chapman conference on Communicating Climate Science. The AGU posted the video up on Youtube, here.
He discussed climate sensitivity at minute 11:42. He went over the very large body of evidence that has led him and many others to conclude climate sensitivity is in the range 2.2 – 4.8 K for doubled CO2 “which agrees with IPCC estimates”. He said: “you will hear a lot of noise from people who pick out one bit out of all this evidence”.
He discussed the work of the PALAEOSENS project, which he said was a very large group of people who came together to try to figure out what paleoclimate data indicates sensitivity is. He pointed out that the most probable value in the PALAEOSENS distribution is 3 C for doubled CO2.
“They get essentially the same answer as everyone has been getting all the time by pulling together the full suite of paleoclimate evidence”.
He pointed out that of all the studies that fed into the PALAEOSENS project, one was seized upon by high level security and political types, bloggers and reporters, etc. It was the lowest one. “Its fairly clear to a lot of us its a lowball study”.
Later on in the conclusion of his talk, around minute 42:21, he said: “Climate science remains robust. I don’t see any serious reason to change sensitivity….”