New research published in Science Advances indicates that northern permafrost regions will transition from a carbon sink to a carbon source as early as the 2050s. This shift contradicts previous Intergovernmental Panel on Climate Change (IPCC) projections, which relied on models assuming these lands would continue to sequester carbon through 2100. The findings suggest that current global climate targets may significantly overestimate the remaining carbon budget available to humanity.
Why current climate models are missing deep carbon deposits
Most global climate models, including those within the CMIP6 framework, rely on the CENTURY model, a system originally designed in the 1980s to simulate grassland soils. According to the Science Advances study, this framework uses conceptual carbon pools based on turnover time rather than physical depth. Because it ignores the physical reality of Arctic terrain, the model fails to account for massive deposits of Yedoma—ice-rich, organic-rich soil—and deep peat layers.
The northern permafrost region covers 15% of the Northern Hemisphere’s land surface but holds approximately one-third of the Earth’s total soil organic carbon.
Researchers updated the ORCHIDEE-MICT model to incorporate up to 20 meters of Yedoma and 10 meters of peat carbon. By integrating these previously excluded depths, the team found that preindustrial organic carbon stocks were 226 petagrams (Pg C) higher than previously estimated. Crucially, this additional carbon is concentrated in “active” and “slow” pools, making it highly vulnerable to decomposition once thawing occurs.
When will permafrost become a net carbon source?
Under the updated ORCHIDEE-MICT model, the northern permafrost region is projected to become a net carbon source by approximately 2055 under high-emission scenarios. This marks a sharp departure from the old model, which predicted the region would remain a net sink, ending the century with a gain of up to 65 Pg C. The new projection suggests a net loss of 3 to 32 Pg C by 2100.
The research team notes that these figures represent a conservative lower bound. The model does not currently account for several accelerating factors, including:
- Abrupt thaw: The formation of thermokarst lakes that rapidly expose deep soil.
- Wildfire interactions: Increased burning of the Arctic landscape.
- Methane release: Ongoing emissions that are not fully captured by current simulations.
- Nutrient cycling: Feedback loops that could further destabilize soil carbon.
How this pattern of underestimation affects global policy
The discrepancy in permafrost modeling mirrors a recurring trend in climate science where initial estimates failed to capture the speed of environmental change. Similar to the permafrost findings, updated ocean models now suggest the Atlantic Meridional Overturning Circulation (AMOC) could collapse between mid-century and 2100—a scenario previously deemed highly unlikely by IPCC-class models. Likewise, early ice sheet models underestimated sea-level rise from Antarctica until researchers integrated data on hydrofracturing and Marine Ice Cliff Instability.
These revisions consistently reveal that previous environmental benchmarks were too optimistic. As the Amazon rainforest has also shifted from a carbon sink to a source due to drought and deforestation, the cumulative effect of these “conservative” model errors forces a re-evaluation of the 2 degrees Celsius warming target. If northern soils turn into carbon emitters decades earlier than expected, human-driven emissions must be reduced more aggressively to compensate for the loss of this natural buffer.
Frequently Asked Questions
What is Yedoma?
Yedoma is an ice-rich, organic-rich deposit found in northern permafrost regions. It contains massive amounts of carbon that have been frozen for thousands of years and is highly susceptible to rapid decomposition when it thaws.
Why did older models treat permafrost as a carbon sink?
Older models, specifically those using the CENTURY framework, predicted that rising temperatures would increase plant growth in the Arctic. They assumed this increased vegetation would absorb enough carbon dioxide to offset the carbon released by thawing soil.
Are these projections definitive?
No. The researchers emphasize that their 2050 timeline is a conservative estimate. Because the model excludes factors like methane emissions and abrupt thaw, the transition to a carbon source could occur even sooner.
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