Hidden geological process offsets carbon emissions from thawing permafrost

A study published in Nature suggests that thawing permafrost may have an unexpected effect on the carbon cycle. While melting frozen ground is widely known for releasing greenhouse gases, researchers found that it can also strengthen a natural process that removes carbon dioxide (CO₂) from the atmosphere.

The research was conducted by scientists from Umeå University in Sweden and East China Normal University in China.

Thawing Permafrost Can Increase CO₂ Removal

As global temperatures rise, permafrost is thawing across many regions, exposing long-frozen organic matter. Microbes break down this ancient carbon and release greenhouse gases, leading many scientists to view thawing permafrost primarily as a growing source of emissions.

However, the new study points to another process taking place at the same time. As frozen ground degrades, previously buried minerals become exposed and water interacts more extensively with rock surfaces. These changes accelerate chemical weathering, a process that can consume atmospheric CO₂.

According to the researchers, this weathering-driven carbon uptake can significantly reduce the amount of CO₂ released by rivers. In some cases, it can even completely offset those emissions.

To investigate the phenomenon, the team studied 50 rivers across the Qinghai-Tibet Plateau, the world's largest high-altitude cryosphere outside the polar regions. They analyzed river CO₂ emissions, dissolved carbon, isotopic tracers, and geochemical models to better understand how thawing permafrost affects carbon cycling.

Their results showed that thawing landscapes enhance chemical weathering, moving carbon into dissolved inorganic forms while simultaneously removing CO₂ from the atmosphere.

Carbon Uptake Can Surpass River Emissions

"We found that river CO₂ emissions decline while carbon uptake through rock weathering increases as permafrost cover decreases," said Liwei Zhang, biogeochemist at East China Normal University. "In some catchments where permafrost has become patchier, weathering-driven carbon uptake was large enough to offset or even exceed river CO₂ emissions."

Across the study area, the researchers estimated that rock weathering offsets about 35 percent of river CO₂ emissions on average.

The effect varied depending on the extent of permafrost coverage. Areas with continuous permafrost showed only modest offsets. In contrast, regions with discontinuous or isolated permafrost sometimes experienced weathering-driven carbon uptake that exceeded 100 percent of river CO₂ emissions. These findings indicate that carbon removal through geological processes can, in some situations, rival carbon release from biological activity.

Geological and Biological Carbon Cycles Interact

The study challenges the idea that thawing permafrost functions only as a source of carbon emissions.

When frozen soils thaw, rivers receive large amounts of ancient organic carbon. Microorganisms then convert some of that material into greenhouse gases that enter the atmosphere. The new findings suggest that geological processes occurring alongside these biological processes may help offset part of those emissions.

The researchers emphasize that rock weathering should not be viewed as a simple or permanent solution to climate change. Carbon cycling in thawing environments is highly complex, and some weathering reactions can release CO₂ depending on the minerals involved.

Instead, the study highlights an important mechanism that is not fully represented in many climate and carbon cycle models.

"Our findings show that biological and geological carbon cycles are tightly linked," says Jan Karlsson, professor at Department of Ecology, Environment and Geoscience at Umeå University. "To understand whether thawing permafrost ultimately amplifies or dampens climate warming, we need to consider both the carbon released from ancient soils and the carbon consumed through rock weathering."

The researchers say future climate assessments should look beyond biologically driven carbon emissions alone and account for geological sources and sinks that emerge as frozen landscapes continue to thaw.