I just finished reading through the second part of the GISS-E climate modelling paper. I’ll write a summary later, either a technical one for or a non-technical one for here, but that’s going to take a while, and this is important.
Everyone, you need to read this document carefully, specifically sections 6-8, including the figures. Those sections require not much more than knowing what a standard deviation is and that a “climate forcing” means “any input to the ecosystem that can affect climate.” The first five sections, short version, say that the model has proven pretty good at predicting global-scale climate change for 1880-2003, it’s not as good at predicting regional change, and its main weaknesses are an ocean model that doesn’t understand El Niño and a sea ice model that nobody really trusts. My professional opinion is that it’s definitely good enough to rely on its numbers for global-scale analyses, but it may underestimate ice melting. (And the authors freely admit the latter)
Sections 6-8 talk about their models for the period 2003-2100, according to five models: “alternative”, “2C”, and three from the Intl Panel on Climate Change.
I know this is a bit of a technical thing to be asking people to read, but this is probably the most important thing that’s crossed my desk in years, and we need to start planning urgently. Pay particular attention to figures 19, 20 and 22.
Ladies and gentlemen, we have a problem. This outweighs anything on the political arena short of global thermonuclear war. I don’t think I could summarize what IPCC scenario A2 would look like by 2100 and have you believe me; but I would say that that scenario implies a real chance of a major population collapse, up to and including extinction and certainly impacting the viability of civilization.
The good news is, the two best scenarios (Alt and 2C) would leave us coming out fairly OK, and both of those are reachable with modern technology and not too much trouble; getting from here to there seems to require policy changes rather than anything enormously terrifying. The figures in the paper describe what emissions goals we would have to hit.
I’ll write up a more detailed summary later, and try to pull the key information out of this document.