Yale Environment 360: The latest report from the Intergovernmental Panel on Climate Change (IPCC) for the first time sets a cap on the amount of carbon emissions we can allow into the atmosphere before calling a complete and permanent halt -- if, that is, we are serious about keeping global warming below two degrees Celsius. That cap was set last month at a trillion tons of carbon. We are something over half way there, with time fast running out.
But where did this figure come from; why has a measure of cumulative...