Globally, May was 0.63 degrees Celsius warmer than the average May between 1981 and 2010, making it the warmest May in this data record, the Copernicus Climate Change Service said.
May’s increase follows a clear trend recorded by Copernicus over the past year. In the last 12-month period up to May, global temperatures were 0.7 degrees Celsius warmer than average — matching the previous year-long high between October 2015 and September 2016.
Europe generally was slightly colder than average, but with sharp geographical differences, the report said.
The most striking spike was in Siberia, the typically freezing region that spans much of Russia, which was up 10 degrees Celsius on average levels.
An environmental group has described the damage as “catastrophic,” and the concentration of contaminants in nearby waters has already exceeded permissible levels tens of thousands of times over, according to Russian environmental agency Rosprirodnadzor.
Two thirds of Russia sits on permafrost, which is degrading rapidly, puncturing places with giant sinkholes.
It follows a remarkably warm winter in Russia, which would usually be blanketed in snow at the start of a year.