Scientists worked on the Tibetan Plateau, analysing 50 rivers in the headwaters of Asia's largest river basins. ©L.Zhang
An EPFL study shows that permafrost thaw not only releases large amounts of carbon but can also trigger processes that remove it from the atmosphere. The study's findings will help improve climate models.
Permafrost thaw is generally seen as a significant source of greenhouse gas emissions. But a study published in Nature shows that it can also trigger processes that remove carbon dioxide (CO₂) from the atmosphere, revealing a more complex picture of the Earth's climate system.
Permafrost - permanently frozen ground - covers roughly a quarter of the Earth's land surface, mainly in the Arctic, but also in Antarctica and mountainous regions such as the Alps. As temperatures rise, thawing permafrost releases ancient carbon that has been locked away for millennia. Some of this carbon is converted into either CO₂ or methane (CH₄), both of which are released into rivers and the atmosphere, further intensifying global warming. Scientists refer to this as a positive feedback mechanism - a process that amplifies its original effect. This is why permafrost is often described as a "ticking time bomb."
A new study, however, finds that several biological and geological processes associated with permafrost thaw can also help remove CO₂ from the atmosphere. Working in rivers on the Tibetan Plateau, an international team of researchers - including scientists from EPFL's River Ecosystems Laboratory (RIVER) - discovered an effect that remains largely overlooked in climate models and could partly counteract this positive feedback mechanism. The effect in question is rock weathering, by which the physical and chemical properties of rocks are altered when they come into contact with water and its constituent substances.
Rock weathering offsets 78% of river CO₂ emissions on average
As the climate has warmed, minerals trapped within and beneath frozen soils have been released, in turn influencing the carbon cycle. The researchers found that this process acts as a substantial carbon sink, offsetting between 15% and 100% - for an average of 78% - of river CO₂ emissions.
"We were surprised by the scale of the effect," says Tom Battin, director of the RIVER laboratory and co-author of the study. "Another unexpected result was the extent to which organic and inorganic carbon fluxes interact." Until now, scientists lacked detailed measurements showing how biological and geological processes work together to influence CO₂ dynamics in rivers across permafrost regions. "In our study, we carefully quantified how the ratio between CO₂ sequestration and release changes when permafrost melts," adds Battin.
The team of researchers from Germany, China, Sweden, Switzerland, the United Kingdom and the United States examined how rivers across the Qinghai-Tibet Plateau - the world's largest continuous cryosphere outside the Arctic and Antarctica - exchange CO₂ with the atmosphere.
Rock weathering becomes stronger as permafrost thaws
The scientists combined CO₂ measurements with chemical and isotopic analyses from 50 rivers in the headwaters of Asia's largest river basins - an area spanning roughly 780,000 square kilometers, at elevations ranging from 1,650 to 4,820 meters above sea level.
In some locations covered by the study, permafrost is continuous. In others, it is patchy or has disappeared altogether. The researchers analyzed the spatial distribution of their data to examine how permafrost thaw had shaped the biogeochemistry of rivers across the Tibetan Plateau over timescales of several centuries. They found that carbon fluxes generated by chemical weathering could play an increasingly important role as permafrost thaws, potentially exceeding the CO₂ emissions produced when organic carbon is converted within rivers.
"Across the region we studied, weathering-driven carbon sequestration offsets 35% of CO₂ emissions from rivers," says Liwei Zhang, a biogeochemist at East China Normal University, who led the study with Aaron Bufe, a professor of sedimentology at Ludwig Maximilian University of Munich (LMU). "What's particularly striking is how strongly this ratio is linked to permafrost degradation."
In areas with continuous permafrost, weathering offsets only about 15% of emissions. By contrast, in places where permafrost only exists sporadically, this figure can increase to more than 100%, suggesting that rock weathering plays an increasingly important role as the rate of permafrost thawing increases.
The outcome also depends on which minerals are released. Across much of the Qinghai-Tibet Plateau, silicate-rich rocks dominate. There, weathering can help offset carbon released from permafrost soils. The opposite can happen where sulfur-bearing minerals such as pyrite are present, as their weathering may increase CO₂ emissions.
A powerful effect, but not a climate fix
The findings from the Qinghai-Tibet Plateau offer new insights into how permafrost thaw influences the balance between carbon sources and carbon sinks. So could rock weathering ultimately counteract human-driven climate change?
"Unfortunately, the answer is no," says Bufe. "Human activity emits around 100 times more CO₂ each year than silicate weathering removes from the atmosphere. Even if permafrost thaw causes a slight increase in weathering rates, the effect will remain far too small. The only real solution is to drastically cut our emissions."
"Rock weathering can counteract river CO₂ emissions induced by permafrost thaw," published on 17 June 2026 in Nature.
