To prevent the projected 3-degree-Celsius temperature increase, greenhouse-gas emissions would need to have ceased entirely between 1960 and 1970, the model found. In that sense, Earth blew by a climactic point of no return 50 years ago — before much of the public understood the realities of climate change.
Earth's temperatures are already on track to blow past the Paris agreement's goals. Last year was the second warmest on record for surface temperatures and the hottest ever for oceans. Polar melting is on track to raise seas 3 feet by 2100 and threatens to displace hundreds of millions of people.