In May, surface temperatures in parts of Siberia were up to 10 degrees C above average, according to the EU's Copernicus Climate Change Service (C3S). Martin Stendel, of the Danish Meteorological Institute, said the abnormal May temperatures seen in north-west Siberia would be likely to happen just once in 100,000 years without human-caused global heating.
Freja Vamborg, a senior scientist at C3S, said that "it is undoubtedly an alarming sign, but not only May was unusually warm in Siberia. The whole of winter and spring had repeated periods of higher-than-average surface air temperatures."
"Although the planet as a whole is warming, this isn't happening evenly. Western Siberia stands out as a region that shows more of a warming trend with higher variations in temperature. So to some extent, large temperature anomalies are not unexpected. However, what is unusual is how long the warmer-than-average anomalies have persisted for," she said.
For her part, Marina Makarova, the chief meteorologist at Russia's Rosgidromet weather service, said that "this winter was the hottest in Siberia since records began 130 years ago. Average temperatures were up to 6 degrees C higher than the seasonal norms."
Meanwhile, on a global scale, the Siberian heat is helping push the world towards its hottest year on record in 2020, despite a temporary dip in carbon emissions owing to the COVID-19 pandemic.
Temperatures in the polar regions are rising fastest because ocean currents carry heat towards the poles, and reflective ice and snow are melting away.
Russian towns in the Arctic circle have recorded extraordinary temperatures, with Nizhnyaya Pesha hitting 30 degrees C on June 9 and Khatanga, which usually has daytime temperatures of around 0 degrees C at this time of year, hitting 25 degrees C on May 22.
Robert Rohde, the lead scientist at the Berkeley Earth project, said Russia as a whole had experienced record high temperatures in 2020, with the average from January to May 5.3 degrees C above the 1951-1980 average. "[This is a] new record by a massive 1.9 degrees C," he said.
In December, Russia's president, Vladimir Putin, had already commented on the unusual heat in the country: "Some of our cities were built north of the Arctic Circle, on the permafrost. If it begins to thaw, you can imagine what consequences it would have. It's very serious."
These freak temperatures have been linked to wildfires, a massive oil spill, and a plague of tree-eating moths that, at the same time, are the effect of global warming.