RAYMOND ZHONG and KEITH COLLINS / NEW YORK TIMES – The numbers are in, and scientists can now confirm what month after month of extraordinary heat worldwide began signaling long ago. Last year was Earth’s warmest by far in a century and a half.

Global temperatures started blowing past records midyear and didn’t stop. First, June was the planet’s warmest June on record. Then, July was the warmest July. And so on, all the way through December …