Nicholas Thompson, "Terrible News About Carbon and Climage Change", The New Yorker 5/12/2013:
We’ve got more carbon dioxide in the atmosphere now than at any point since the Pliocene, when there were jungles in northern Canada. And the number hurdles ever upward, as ocean levels rise and extreme weather becomes routine. Three-fifty was the old target; four-fifty is the new one. But what indication is there that we’ll stop at five hundred, six hundred, or even more?