Last year shattered 2014’s record to become the hottest year since reliable record-keeping began, two U.S. government science agencies announced Wednesday in yet another sign that the planet is heating up.

 

2015’s sharp spike in temperatures was aided by a strong El Niño weather pattern late in the year that caused ocean waters in the central Pacific to heat up. But the unusual warming started early and steadily gained strength in a year in which 10 of 12 months set records, scientists said.