Hansen: "if humanity wishes to preserve a planet similar to that on which civilization developed and to which life on earth is adapted, paleoclimate evidence and ongoing climate change suggest that CO2 will need to be reduced from its current 385 ppm to at most 350 ppm."
McKibben goes on:
Hansen cites six irreversible tipping points -- massive sea level rise and huge changes in rainfall patterns, among them -- that we'll pass if we don't get back down to 350 soon; and the first of them, judging by last summer's insane melt of Arctic ice, may already be behind us.
Two weeks ago came the news that atmospheric carbon dioxide had jumped 2.4 parts per million last year -- two decades ago, it was going up barely half that fast. And suddenly, the news arrives that the amount of methane, another potent greenhouse gas, accumulating in the atmosphere, has unexpectedly begun to soar as well.
Apparently, we've managed to warm the far north enough to start melting huge patches of permafrost and massive quantities of methane trapped beneath it have begun to bubble forth.
A beetle, encouraged by warmer temperatures, has already managed to kill 10 times more trees than in any previous infestation across the northern reaches of Canada this year. This means far more carbon heading for the atmosphere and apparently dooms Canada's efforts to comply with the Kyoto Protocol, already in doubt because of its decision to start producing oil for the U.S. from Alberta's tar sands. . .In an earlier piece, McKibben wrote as follows:
for the past twenty years, the period during which greenhouse science emerged, most of the effects of heating on the physical world have in fact been more dire than originally predicted. The regular reader of Science and Nature is treated to an almost weekly load of apocalyptic data, virtually all of it showing results at the very upper end of the ranges predicted by climate models, or beyond them altogether.
Compared with the original models of a few years ago, ice is melting faster; forest soils are giving up more carbon as they warm; storms are increasing much more quickly in number and size.