And climate advocates wonder why the public is confused about global warming. Thus writes David Biello in SciAm:
Despite decades of effort, scientists do not know precisely what temperatures or greenhouse gas concentrations in the atmosphere constitute a danger.
Biello goes on to survey leading climate scientists on various threshold levels, who bascially throw up their hands, (except, of course, James Hansen). Among others quoted, Columbia University's Wallace Broecker continues to talk about the inevitably of some frightening numbers:
We're at 387 now and we're going up at two ppm per year. That means 450 is only 30 years away. We'd be lucky if we could stop at 550.