This year's Arctic fire season - yes, that's now a thing - began two months earlier than in the past, driven by 'zombie fires' from the year before that hadn't completely gone out, scientists say.
The "unprecedented" burning is now taking place in parts of the Arctic previously thought immune to wildfires, including "dwarf shrubs, sedges, grass, moss, even surface peats".
"Wet landscapes like bogs, fens, and marshes are also becoming vulnerable to burning," University of Colorado at Boulder scientists said this week.
"It's not just the amount of burned area that is alarming," said Merritt Turetsky, fire and permafrost ecologist at the University of Colorado Boulder. "There are other trends we noticed in the satellite data that tell us how the Arctic fire regime is changing and what this spells for our climate future."
Many of the blazes are "on permafrost with a high percentage of ground ice".
"Nearly all of this year's fires inside the Arctic Circle have occurred on continuous permafrost, with over half of these burning on ancient carbon-rich peat soils," said study co-author Thomas Smith, fire scientist at the London School of Economics and Political Science.
"The record high temperatures and associated fires have the potential to turn this important carbon sink into a carbon source, driving further global heating."
Climate models which scientists use to predict the future don't typically include carbon sequestered in permafrost - they're meant to be permanently frozen, after all.
But fires from last year's devastating Arctic fires stayed smouldering underground over the northern hemisphere winter, roaring back into life this recent summer.
"We know little about the consequences of holdover fires in the Arctic," said Dr Turetsky, "except that they represent momentum in the climate system and can mean that severe fires in one year set the stage for more burning the next summer."
There were early signs of the sheer scale of this year's wildfires, which are on course to outpace last year's record-setting season.
"We know that temperatures in the Arctic have been increasing at a faster rate than the global average, and warmer/drier conditions will provide the right conditions for fires to grow when they have started," Mark Parrington, senior scientist at the European Union's Copernicus Atmosphere Monitoring Service, said earlier this month.
"Data... shows that typically fires in the Arctic Circle occur in July and August, so it has been unusual to see fires of this scale and duration in June."
The total carbon output of this year's blazes will be about a third higher than 2019's, which were also called "unprecedented" at the time. This year's fires appear to have gone more under the radar, with the world facing a more immediate problem in the coronavirus pandemic.
But unlike COVID-19, climate change won't be fixed via a vaccine. Another study published this week, this one out of the University of Buffalo, concludes more of Greenland's ice will melt this century than any other in the past 12,000 years.
Depending on how global efforts to stem climate change go, they predict between 8.8 trillion and 35.9 trillion tonnes of ice will melt, reversing 4000 years of constant growth.
If Greenland's ice sheet completely melts - as the scientists say it is likely to in the next 1000 years - it will contribute six metres to sea level rises.
In August, scientists said it was likely the ice melting was beyond the point of no return, and a study late last year found it was melting seven times faster now than in the 1990s.
