Summary
Now, there's a big margin of error when you are dealing with 35 million years ago: plus or minus 75 ppm, in this case. That means that the fatal number when all the ice disappears could be as high as 500 ppm -- or it could be as low as 350 ppm. If that is the range within which all the world's ice will eventually melt, and you like living in the Holocene, then you probably should not put all your money on a 450-ppm ceiling for CO2.
So [James Hansen] is spearheading a campaign to get 350 ppm recognized as the real long-term target we should be aiming at. Tricky, since we are already at 387 ppm and rising fast, but last week, when I spoke to him at the Tallberg Forum's annual conference in Sweden, he explained: "To figure out the optimum is going to take a while, but the fundamental thing about the 350 (ppm target), and the reason that it completely changes the ball game, is precisely the fact that it's less than we have now.""Even if the optimum turns out to be 325 or 300 or something else, we've go to go through 350 to get there. So we know the direction now that we've go to go, and it's fundamentally different. It means that we really have to start to act almost immediately. Even if we cut off coal emissions entirely, CO2 would still get up to at least 400, maybe 425, and then we're going to have to draw it down, and we're almost certainly going to have to do it within decades."See the full content of this document
Extract
Road to 35 Million Bc
Global-warming expert believes Earth has passed safe CO2 level
Gwynne Dyer'Damn! I think we just passed the last exit for the Holocene!""I'm sorry, honey, I wasn't looking.""We have to get off this highway. What's the next exit?""It's a long wa...See the full content of this document
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