Humans can emit about 1,000 more gigatons of carbon dioxide before we lock in a global average temperature increase of more than 2C from before the Industrial Revolution, the threshold beyond which scientists warn that changes to the climate get dangerous. A higher-than-2C planet might trigger runaway effects that would make things even worse.
The new year will arrive with the average temperature already up about 1.2C. More than halfway there. Every year, we’re releasing more than 35 gigatons of CO₂ and pushing up its concentration in the air by about 2.5 parts per million. Keeping our collective fever under the 2C targeted by signatories to the Paris Agreement or even better, below the 1.5C they’d prefer—is already looking very difficult.