Polar bears play on the Arctic sea ice. Photo: VCG

Temperatures soared 10 C above average across much of permafrost-laden Siberia in June, which was tied for the warmest June on record globally, the European Union's climate monitoring network said on Tuesday.

The 12-month period to June 2020 was also tied for the warmest to date across the planet, on a par with the ones ending in May and September 2016, an exceptional El Nino year, the Copernicus Climate Change Service (C3S) reported.     

That means Earth's average surface temperature for July 2019-June was 1.3 C above preindustrial levels, the standard benchmark for global warming.

The 2015 Paris climate treaty calls for capping the rise in temperature to "well below" 2 C. In 2018, however, the UN's climate science panel (IPCC) concluded in a landmark report that 1.5 C - only two-tenths of a degree above the new 12-month high - is a far safer guardrail.

In the Arctic, meanwhile, an hourly temperature record for June - 37 C - was set on June 21 near Verkhoyansk in northeastern Russia, where a weather station logged a blistering 38 C on the same day. The previously registered Arctic hourly highs in 1969 and 1973 were at least 1 C cooler.

Freakishly warm weather across large swathes of Siberia since January, combined with low soil moisture, have contributed to a resurgence of wildfires that devastated the region in the summer of 2019, C3S reported. Both the number and intensity of fires in Siberia and parts of Alaska have increased since mid-June, resulting in the highest carbon emissions for the month - 59 million tons of CO2 - since records began in 2003.

"Last year was already by far an unusual, and record, summer for fires in the Arctic Circle," said Mark Parrington, senior scientist at the EU's Copernicus Atmosphere Monitoring Service, warning of "intense activity" in the coming weeks. Copernicus has said that "zombie" blazes that smoldered through the winter may have reignited.

Globally, June 2020 was more than 0.5 C warmer than the 1981-2010 average for the same month, and on a par with June 2019 as the warmest ever registered. Siberia and the Arctic Circle are prone to large year-on-year temperature fluctuations, but the persistence of 2020's warm spell is very unusual, said C3S director Carlo Buontempo. 

"What is worrisome is that the Arctic is warming faster than the rest of the world," he said in a statement.

Across the Arctic region, average temperatures have risen by more than 2 C since the mid-19th century, twice the global average.

Despite lower-than-average temperatures in its western reaches, the whole of Siberia was more than 5 C above normal for June, according to C3S satellite data.

The softening of once solid permafrost - stretching across Siberia, Alaska and northern Canada - has upended indigenous communities and threatens industrial infrastructure.