As Arctic permafrost thaws, microbes can break down long-frozen organic matter and release carbon dioxide (CO2) and methane (CH4). Those emissions add to warming, which can drive further thaw—a climate feedback. But the story is not simply a steady leak of methane: carbon also moves through fires, rivers and vegetation, and the balance varies by place and period.
What is released when permafrost thaws?
Permafrost is ground that stays frozen for at least multiple years. It contains old organic carbon that can remain undecomposed while frozen. When the ground warms, microbes can break down that material, releasing CO2 and, in some conditions, methane. The added greenhouse gases contribute to warming, which can expose more frozen ground and reinforce the cycle.
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Not all carbon follows the same route. It may enter the atmosphere as CO2 or methane, travel in meltwater into rivers, or be taken up by expanding or more productive vegetation. The dominant pathway depends on local landscape and conditions.
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What do recent Arctic observations show?
NOAA’s 2024 tundra assessment
NOAA’s 2024 Arctic Report Card says the Arctic tundra region has shifted to a CO2 source when wildfire emissions are included, and remains a consistent methane source. This is a regional finding, not a claim that every Arctic location emits more carbon than it absorbs. NOAA Arctic Report Card 2024
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Alaska permafrost temperatures and Arctic fires
In the same report, permafrost temperatures in 2024 were the highest on record at nearly half of Alaska’s long-term monitoring stations. Averaged across Alaska, 2024 had the second-warmest permafrost temperatures on record. The report also gives average circumpolar wildfire emissions since 2003 as 207 teragrams of carbon per year; 2024 was the second-highest wildfire-emissions year north of the Arctic Circle. These are wildfire figures, not measurements of emissions from thawing permafrost alone. NOAA Arctic Report Card 2024
A broader study covering 2000–2020
NASA’s summary of research spanning 7 million square miles (18 million square kilometers) of northern permafrost terrain from 2000 to 2020 found that forests took up slightly more CO2 than they released. That uptake was largely offset by emissions from lakes, rivers and fires; lakes and wetlands were methane sources. Across the period, the net greenhouse-gas change contributed to warming. This is an assessment of that geography and period, not a direct measurement of the current year. NASA’s summary of the 2000–2020 analysis
Why the way permafrost thaws matters
Gradual thaw
In gradual thaw, the seasonally thawed active layer—the ground that thaws in summer and refreezes in winter—deepens. That can expose more old organic material to microbial decomposition.
Abrupt thaw and thermokarst lakes
Ice-rich ground can also collapse abruptly, forming features such as thermokarst lakes. In waterlogged, low-oxygen soils, decomposition can produce methane. NASA’s account of a 2018 study reports that abrupt thaw increased estimated permafrost-derived greenhouse warming by 125 to 190 percent compared with gradual thaw alone. That is a study estimate, not a universal percentage for Arctic terrain or a forecast of total planetary warming. NASA’s account of the 2018 abrupt-thaw study
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Is Arctic methane rising everywhere?
No single methane trend applies to every Arctic landscape and time period. A NOAA summary of Barrow measurements published in 2016 reported that the methane record it examined did not show a long-term increase, although it included spikes associated with short-term temperature variation. NOAA cautioned that this did not mean thawing permafrost released no carbon: the carbon could emerge as CO2 or follow other pathways. That historical Barrow finding should not be read as a current, Arctic-wide trend. NOAA’s summary of the Barrow methane measurements
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why different carbon assessments can differ
Whether a region is described as a carbon source or sink depends on what is counted: which greenhouse gases and landscapes, whether wildfire emissions are included, and the years under review. NOAA’s 2024 tundra assessment includes wildfire emissions; NASA’s broader analysis covers northern permafrost terrain from 2000 to 2020 and accounts for multiple land and water pathways. They describe different scopes and periods, not conflicting measurements of precisely the same quantity.
The evidence supports a warming feedback, but it does not establish one precise global forecast for future permafrost warming. The contribution depends on gas, landscape, thaw process, wildfire, vegetation response and the comparison period. The findings do not show that a catastrophic methane release is imminent.
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