Global map of the March 2017 LOTI (land-ocean temperature index) anomaly shows that Europe and all of Russia (especially north central Siberia) were again much warmer than the 1951-1980 base period. Much of the United States was also relatively warm, but Alaska was instead cool.
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.
For more information on NASA GISS’s monthly temperature analysis, visit data.giss.nasa.gov/gistemp.