Thawing permafrost may release billions of tons of carbon by 2100
Among the many effects of global warming this century, the melting of permafrost stands out. Permafrost, found beneath 15% of the northern hemisphere, is composed of frozen organic material that has stored carbon for millennia.
Rising global temperatures prompt questions about how much permafrost will thaw and how much carbon it will release.
The role of permafrost in the carbon cycle
Permafrost is soil, rock, or sediment that has been frozen for two or more consecutive years. It is typically found in polar regions, such as the Arctic, and at high altitudes. In regions where temperatures dip below -5°C, it remains frozen permanently.
During the Last Glacial Maximum, permafrost covered vast areas, but today’s warming – especially in polar regions – threatens its stability.
The Arctic has been warming almost four times faster than the global average since 1979, raising concerns about thawing permafrost releasing carbon dioxide and methane, which would worsen global warming.
Modeling thawing permafrost
Understanding permafrost’s future involves complex modeling. A recent study published in the journal Earth’s Future combines observational data with a biogeochemical model to predict how much carbon thawing permafrost might release.
Study lead author Lei Liu from Zhengzhou University and colleagues incorporated processes such as deep-soil carbon decomposition up to six meters below the surface, doubling the depth of previous studies.
The model also used detailed profiles of soil organic carbon derived from observational datasets. It estimates that the Northern Hemisphere’s permafrost contained 563 gigatons (Gt) of carbon between 2010 and 2015, spread over an area of 14.4 million square kilometers.
Scenarios of permafrost thaw
The study considered two scenarios based on Shared Socioeconomic Pathways (SSPs):
- SSP126: An optimistic scenario limiting global warming to 2.0°C.
- SSP585: A pessimistic scenario assuming continued fossil fuel reliance.
Under SSP126, 119 Gt of carbon would thaw by 2100, reducing permafrost ecosystem carbon by 3.4 Gt. In contrast, SSP585 would see 252 Gt of carbon thawed, with a 15 Gt reduction in ecosystem carbon.
The study projects that only 4% to 8% of this thawed carbon will release into the atmosphere by 2100. This translates to a maximum of 10 Gt of carbon under SSP126 and 20 Gt under SSP585. For context, human activities in 2023 emitted 11.3 Gt of carbon.
While significant, the projected emissions from permafrost thawing remain smaller than annual human emissions.
Carbon release due to permafrost thaw
Thawing permafrost contributes to the carbon cycle in multiple ways. Decomposing organic matter releases nitrogen, which plants can absorb, stimulating growth.
The team’s model showed that nitrogen availability could increase vegetation nitrogen stocks by 10 to 26 million tons and carbon stocks in plants by 0.4 to 1.6 Gt under the two scenarios.
However, this increased plant growth does not fully offset carbon losses from thawed permafrost. Furthermore, thawing alters plant species composition and ecosystem dynamics, with broader implications for the carbon and nitrogen cycles.
The study highlights deeper complications, such as abrupt thaw events, root deepening, and microbial activity – which could accelerate carbon release.
Mitigation challenges and uncertainties
The study highlights the need for decisive action. For warming to cease, human emissions must drop to zero.
As long as warming persists, more permafrost will thaw, creating additional challenges for climate change mitigation. High-latitude and high-altitude regions remain areas of significant uncertainty, where warming impacts and feedback mechanisms are more difficult to predict.
While models like this one improve our understanding, they remain projections that are dependent on socioeconomic choices made by humanity. Will we pursue aggressive climate action or continue with business as usual? The fate of permafrost – and its carbon – rests largely in human hands.
Limiting permafrost thaw
The thawing of permafrost presents a dual challenge: it is both a consequence and contributor to global warming.
While current models suggest limited carbon release this century, the potential for long-term impacts remains significant. Mitigation efforts must intensify to reduce warming, limit permafrost thaw, and minimize its feedback on the climate system.
As Lei Liu’s study highlights, understanding permafrost dynamics is crucial in preparing for a warming world.
The study is published in the journal Earth’s Future.
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