This drastic shift is detailed in NOAA's 2024 Arctic Report Card, which revealed that annual surface air temperatures in the Arctic this year were the second-warmest on record since 1900.

"Our observations now show that the Arctic tundra, which is experiencing warming and increased wildfire, is now emitting more carbon than it stores, which will worsen climate change impacts," said NOAA Administrator Rick Spinrad.

Climate warming has dual effects on the Arctic. While it stimulates plant productivity and growth, which remove carbon dioxide from the atmosphere, it also leads to increased surface air temperatures that cause permafrost to thaw.

When permafrost thaws, carbon trapped in the frozen soil is decomposed by microbes and released into the atmosphere as carbon dioxide and methane, two potent greenhouse gases.

Human-caused climate change is also intensifying high-latitude wildfires, which have increased in burned area, intensity, and associated carbon emissions.

Wildfires not only combust vegetation and soil organic matter, releasing carbon into the atmosphere, but they also strip away insulating soil layers, accelerating long-term permafrost thaw and its associated carbon emissions.

Since 2003, circumpolar wildfire emissions have averaged 207 million tons of carbon annually, according to NOAA. At the same time, Arctic terrestrial ecosystems have remained a consistent source of methane.

"The climate catastrophe we're seeing in the Arctic is already bringing consequences for communities around the world," said Brenda Ekwurzel, a climate scientist at the Union of Concerned Scientists.

"The alarming harbinger of a net carbon source being unleashed sooner rather than later doesn't bode well. Once reached, many of these thresholds of adverse impacts on ecosystems cannot be reversed."