Arctic tundra now emitting more carbon gases than it absorbs, annual report says

For millennia, the tundra regions of the Arctic drew in carbon from the atmosphere and locked it in permafrost.

That is the case no more, according to an annual report issued on Tuesday by the National Oceanic and Atmospheric Administration.

The tundra regions have become a net carbon source rather than a carbon sink, the result of permafrost warming, increased wildfires and other effects of climate change, said the 2024 Arctic Report Card, a NOAA project with nearly 100 collaborating scientists from different organizations in Alaska and elsewhere.

The sink-to-source switch means that carbon-based plant and animal matter that has been stored in permafrost for thousands of years now streams into the air because of warmth-induced decomposition, said Brendan Rogers, a scientist with the Woodwell Climate Research Center and one of the Arctic Report Card’s co-authors.

The fear is that the change will exacerbate the warming caused by carbon gases that envelop the planet and hold in warmth, creating what is called a greenhouse effect, Rogers said on Tuesday.

“There is a concern, of course, with the amount of carbon that’s stored, especially in permafrost. As climate warms, as those soils warm, that could be released. The scientific consensus is that some of that will be released. It could be the equivalent, for example, to a major greenhouse gas-emitting country,” Rogers said at a news conference, held by NOAA at the American Geophysical Union’s annual meeting in Washington, D.C.

The annual report card describes changes in a region of the world that has warmed up at nearly four times the global rate.

The tundra regions’ switchover from sink to source has occurred over at least the last two decades, according to the report card. While there have been some recent years when the tundra region functioned as a net carbon sink, on average it is a net carbon emitter, Rogers said at the news conference.

Permafrost, wildfires and the relationship between them have converted the tundra regions, according to the report.

In Alaska, average permafrost temperatures across an array of long-term monitoring stations were the second highest on record, the report card said. The temperatures were the highest ever recorded at about half of the Alaska sites, the report card said.

Permafrost need not be thawed to emit carbon gases, Rogers said in an interview prior to the report’s release. As soil warms, even if temperatures remain below freezing, microbes become increasingly active and increase their expulsion of carbon dioxide, he said. Such carbon gas respiration is a byproduct when microbes break down organic matter.

Wildfire as a direct and indirect carbon emitter

Wildfires factor into the sink-to-source switchover because of their direct emissions and their effect on permafrost, the report card said.

Wildfires in circumpolar regions have emitted an average of 207 million metric tons of carbon annually since 2003, it said. Those fires are getting more intense, and this year’s fires north of the Arctic Circle emitted the second-highest amount of carbon yet recorded, the report card said.

Wildfires are normal in the boreal forest, which can regrow and absorb carbon from the air through photosynthesis, Rogers said at the news conference.

“What’s the challenge right now is, of course, in areas of permafrost, that those fires will remove the insulating soil organic matter. That permafrost can thaw and lead to longer-term emissions,” Rogers said. “And we’re just seeing this general intensification of wildfires since the mid-20th century, so that they’re emitting that carbon into the atmosphere.”

Concerns about fire unlocking permafrost carbon prompted a new policy in one area of Alaska, the Yukon Flats National Wildlife Refuge. Through consultation with the Woodwell Climate Research Center, a Massachusetts-based research organization, the refuge identified about 1.6 million permafrost-laden acres where fires, if they broke out, would draw responses to limit their burning. Past practice in those areas was to allow fires to burn naturally. The sites put into that classification were identified as holding a type of ice-rich permafrost called yedoma that is considered particularly vulnerable to thaw.

There was no fire suppression this year on any of those newly identified yedoma sites, but one fire that did draw a response burned over a separate area that does likely contain that type of ice-rich permafrost, said Jimmy Fox, the refuge’s superintendent. The Ed Berg Slough Fire flared up in June at a site that had not burned in recent years, and a quick response by firefighters limited it to about 4 acres.

The site would have qualified for the new classification had it not already been designated for what is considered a “modified” firefighting response, Fox said.

“Fortunately, although the fire did not start in a new yedoma protection area, researchers will likely be able to evaluate the event and what effect the suppression may have in protecting yedoma and at what cost,” Fox said by email.

Ted Schuur, a permafrost expert at Northern Arizona University and one of the report’s co-authors, emphasized the long-term nature of the switch.

“What we’re describing is a long-term, 20-year trend towards this increasing source from the tundra region,” he said at the news conference. That trend will be sustained even if there are occasional years when the tundra does soak up more atmospheric carbon than it emits, he said.

Winter emissions, which occur when there is little or no sunlight to enable plant photosynthesis, are particularly high, said Schuur, who has documented the phenomenon in the Denali National Park area and elsewhere in Alaska.

This year’s emissions of carbon dioxide and methane, both of which are greenhouse gases, hit a new record, primarily because of wintertime, Schurr said. He noted that wintertime carbon emissions from tundra had not gotten much study in the past. “So in places that we’re hardly paying attention, we see records being set, and we think it’s very important,” he said.

Continued warming in the air and water

Beyond explaining how the tundra regions have shifted from being net carbon sinks to net carbon emitters, the report card described a continuing long-term trend toward a warmer and wetter Arctic.

Arctic annual surface air temperatures for the 12 months ending in September 2024 ranked second warmest since 1900. An August heatwave set new daily records in several sites in northern Alaska and Canada, the report card noted. The last nine years in the Arctic were the nine warmest on record, the report card said.

The past summer was also the wettest in the Arctic on record, it said. Despite above-average snow accumulation in the past year across the Arctic, the snow season was compressed in some places. In parts of Arctic Canada, the snow season was the shortest in 26 years, and overall, Arctic snowmelt is occurring one or two weeks earlier than it did historically, the report card said.

The sea ice minimum extent reached in September was the sixth lowest in the satellite record. All 18 lowest annual minimums have happened in the last 18 years.

Arctic greening, a satellite-based measurement of the northward expansion of woody shrubs and other plants as the environment warms, was the second highest on record, the report card said. The greening trend has been measured since 1990. Even though that new plant growth results in more intake of atmospheric carbon dioxide during the growing season, that amount of absorption is outweighed by the amount of carbon emitted from the ground and from the plants themselves during the dark non-growing season, the report card said.

There were regional variations and outliers.

One was the Chukchi Sea off northwestern Alaska. Most areas in the seas around the Arctic Ocean had August sea surface temperatures that were 2 degrees Celsius to 4 degrees Celsius, or 3.6 degrees to 7.2 degrees Fahrenheit, warmer than the 1991-2020 August average. However, the Chukchi was 1 degree to 4 degrees Celsius, roughly 1.82 degrees to 7.2 degrees Fahrenheit, cooler than that past average.

Melt on the Greenland Ice Sheet was a bit of an anomaly from the more long-term trend. This year’s loss of Greenland ice was the smallest since 2013, the result of more snowfall than usual, the report card said.

Each year’s report card focuses on some specific Arctic species, and this year’s document described warming effects on tundra caribou and Alaska’s ice-dependent seals.

Uncertain future

NOAA has released the Arctic Report Card every year since 2006. Next year’s report is scheduled to be the 20th in the series. That means 2025 “will be a big event for the Arctic report card,” said Twila Moon, a lead editor of this year’s report and a scientist at the National Snow and Ice Data Center in Colorado.

That report is already in the works, she said at the news conference.

“The Arctic report card is a year-round effort, and we’ll be thinking about the next one as soon as we wrap up this one,” she said.

But the fate of the annual report card and NOAA itself are uncertain in the incoming Trump administration

NOAA, including its National Weather Service, is one of the federal agencies that may be slashed by the incoming administration. The conservative Heritage Foundation’s blueprint for remaking the federal government, called Project 2025, proposes deep cuts to NOAA and privatization of many of its functions, including those of the National Weather Service. There are fears among scientists that the incoming administration’s cost-cutting plan led by billionaire Elon Musk and former presidential candidate Vivek Ramaswamy will gut NOAA and its services.

President-elect Donald Trump has long opposed action to combat climate change, which in the past he called a hoax, and he has cast doubt on climate scientists’ reports.

NOAA Administrator Rick Spinrad, speaking at the news conference, expressed optimism nonetheless about the agency continuing its work to document climate change in the Arctic and elsewhere and to help people combat and adapt to it.

NOAA, he said, is a “mission agency” with science that responds to needs that continue to grow with intensifying events like wildfires, floods, drought and coastal inundation.

“In fact, the argument I would make is that now more than ever, the need, the requirement, the demand signal, if you will, is higher than ever before,” he said.

There can be changes to make the investments more efficient, but studies have shown that “the return on those investments is extraordinary, in many cases, 10-to-1 in terms of protection of lives and property,” he said.