Last month was the second-warmest May in 137 years of modern record-keeping of average global temperatures, according to NASA.
The two top May temperature anomalies have occurred during the past two years. 2016 was the hottest on record, at 0.93 degrees Celsius warmer than the May mean temperature.
Last month was 0.88 degrees Celsius warmer than the mean May temperature from 1951-1980.
This year's May temperature was 0.05 degrees Celsius cooler than last year. It was just 0.01 degrees Celsius warmer than the third warmest May, which occurred in 2014.
The monthly analysis by scientists at NASA's Goddard Institute for Space Studies (GISS) is assembled from publicly available data acquired by about 6,300 meteorological stations around the world, ship- and buoy-based instruments measuring sea surface temperature, and Antarctic research stations.
The modern global temperature record begins around 1880 because previous observations didn't cover enough of the planet.