May 2018 was the fourth warmest May, and the period March-April-May was the third warmest Northern Hemisphere spring in 138 years of modern record-keeping, according to a monthly analysis of global temperatures by scientists at NASA’s Goddard Institute for Space Studies (GISS) in New York.
Last month and N.H. spring were respectively +0.82 °C and +0.86 °C warmer than the corresponding averages of the 1951-1980 period. Only May 2016 (+0.91 °C), 2017 (+0.88 °C) and 2014 (+0.85 °C) were warmer than the past month and only the springs of 2016 (+1.10 °C) and 2017 (+0.97 °C) surpassed this year’s spring.
The monthly analysis by the GISS team 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. Monthly analyses are sometimes updated when additional data becomes available, and the results are subject to change.