The math the planet relies on isn’t adding up right now

As over 150 nations assemble to sign the Paris climate agreement in New York on Friday, reams of new analysis are pouring out from the planet’s vital number-crunchers, who look at the fundamental relationship between how much carbon we put in the air and how much the planet’s temperature increases as a result.
And it’s adding up to a somber verdict: We seem closer to must-avoid climate thresholds than we thought — and crossing them may have bigger consequences than we recognize.