If you’re worried about global warming, here’s some more bad news. The National Oceanic and Atmospheric Administration reports that May 2014 had the highest combined global average temperature (both land and ocean) ever recorded for that month at 59.93 degrees F.

That was 1.33 degrees above the 20th Century average for May, a bump that’s tied for the highest increase ever for any month of the year in temperature records, which go back to 1880.

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While a temperature record in a single month isn’t necessarily proof of long-term climate change, this one is part of an increasingly alarming pattern. Four of the five warmest Mays on record have occurred in the past five years: 2010 (second warmest), 2012 (third warmest), 2013 (fifth warmest), and 2014 (warmest); currently, 1998 has the fourth warmest May on record.  And the entire March-to-May spring season was the second-hottest in the global temperature records, exceeded only by 2010.

If you’re wondering how scientists figure out average temperatures for the entire planet, the data is compiled with the help of the Global Historical Climatology Network, an array of more than 75,000 weather stations in 180 countries and territories across the planet.

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In addition to recording low and high temperatures in those locations each day, the stations also gather data on precipitation. (Some of the older stations have been keeping records since the early 1800s.) That data is augmented by NOAA’s constellation of orbital satellites, which gather weather information from space.

Photo: This map shows how temperatures in various locations across the globe diverged in May from the norm for 1981-2010. Credit: NOAA