After trapping carbon dioxide in its frozen soil for millennia, the Arctic tundra is undergoing a dramatic change brought on by frequent wildfires that are turning it into a net source of carbon dioxide emissions, a US agency reported.
This abrupt change is detailed in the National Oceanic and Atmospheric Administration's Arctic Report 2024, which reveals that annual surface air temperatures in the Arctic that year were the second warmest since 1900.
"Our observations now show that the Arctic tundra, which is experiencing warming and increased fires, is now releasing more carbon than it is storing, which will exacerbate the effects of climate change," NOAA Administrator Rick Spinrad said.
The finding is based on averages of observations recorded between 2001 and 2020.
Climate warming is having a double impact on the Arctic. It boosts productivity and plant growth, which pull carbon dioxide out of the atmosphere, but it also causes surface air temperatures to rise, leading to permafrost thawing.
The thawing of permafrost releases carbon that was previously trapped in the frozen ground in the form of carbon dioxide and methane - two powerful greenhouse gases - through microbial decomposition.
The report states that in 2024, Alaska will record the second warmest permafrost temperature on record.
Human-caused climate change is also intensifying high-latitude wildfires, which are increasing in burned area, intensity and associated carbon emissions.
Forest fires not only burn vegetation and soil organic matter, releasing carbon into the atmosphere, but also destroy insulating soil layers, accelerating long-term thawing of permafrost and associated carbon emissions.
According to NOAA, emissions from wildfires in the circumpolar region have averaged 207 million tons of carbon per year since 2003. At the same time, Arctic terrestrial ecosystems remain a constant source of methane.
"Last year, 2023, was the biggest fire year on record due to Canadian wildfires burning more than twice in any other year in Canadian history," report co-author Brendan Rogers said at a news conference.
The fires have emitted nearly 400 million tonnes of carbon dioxide - more than two and a half times the emissions from all other sectors in Canada combined, he added.
Meanwhile, 2024 is the second-largest year for wildfire emissions within the Arctic Circle.
Asked whether the Arctic's shift from a sink to a source of carbon dioxide could be permanent, Rogers said that remains an open question. While boreal forests in the south still serve as carbon sinks, northern regions are more troublesome.
"There is definitely interannual variability," he stressed. "What I'm reporting here is the average condition we've seen over a 20-year period."
In response to the news, Brenda Ekwurzel, a climatologist with the Union of Concerned Scientists, stated that "the climate catastrophe we're seeing in the Arctic is already having consequences for communities around the world."
"The alarming harbinger of a net unleashing of carbon dioxide sooner rather than later does not bode well. Once reached, many of these thresholds of adverse impact on ecosystems cannot be undone."
As well as getting warmer, the Arctic is also getting wetter, with the summer of 2024 set to see the highest rainfall on record.
The trend is accelerating coastal erosion, threatening indigenous communities that depend on stable ice and traditional hunting practices.
Warmer temperatures are also having an impact on wildlife, with the report stating that tundra caribou numbers have declined by 65% over the past two to three decades - summer heat disrupts their movement and survival, along with changes in winter snow and ice conditions.
Surprisingly, however, Alaska's ice seal populations remain healthy.
The report found no long-term negative impacts on body condition, age at maturity, pregnancy rates, or pup survival of the four species of ice seals - ringed, bearded, spotted, and ribbon - inhabiting the Bering, Chukchi, and Beaufort seas. | BGNES
