Thawing permafrost could tip Earth’s carbon balance

Large parts of the North rest on frozen ground known as permafrost. This ground has remained locked for centuries, holding almost twice as much carbon as today’s atmosphere. But the ice is warming.

As the permafrost thaws, greenhouse gases escape. The big question is whether it will keep absorbing carbon or begin driving more warming.

Researchers from the Chinese Academy of Sciences pulled together results from 1,090 sites across the Northern Hemisphere. The analysis shows warming by around 2°C (3.6°F) splits permafrost into winners and losers. Arctic systems pull in more carbon, while alpine systems weaken as sinks and leak more gases.

“We integrated data from 1,090 independent sites with measured carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) responses to experimental warming across the Northern Hemisphere permafrost regions,” said Bao Tao, first author of the study.

Warming unlocks nitrous oxide surge

High-mountain permafrost is naturally dry. Warming dries it further. Less water means weaker plant growth and faster breakdown of organic matter.

Carbon dioxide emissions rise while carbon uptake falls. Methane absorption increases in these soils, but not enough to cancel out the losses. Nitrous oxide emissions spike sharply, adding another powerful warming agent to the mix.

Nitrous oxide deserves special attention. Although it escapes in smaller amounts, its heat-trapping potential is nearly 273 times stronger than carbon dioxide over a century.

Even modest increases shift the climate balance. In alpine regions, where soils become drier and nitrogen becomes more available, warming unlocks conditions for nitrous oxide to surge.

Arctic plants balance carbon loss

Arctic soils are wetter and packed with vegetation. When warmed, these soils gain even more subsurface water. Plants capture more carbon dioxide, partly balancing what microbes release.

Methane emissions, however, climb in these soggy conditions. The Arctic acts as both a brake and an accelerator in the climate system.

Prolonged warming boosts Arctic vegetation further. More leaves, taller grasses, and denser shrubs drive stronger photosynthesis. That growth helps offset permafrost losses from thawed soils.

Yet methane, produced in waterlogged layers without oxygen, keeps bubbling upward. The result is a tug-of-war in which one gas cancels out part of another’s effect.

Permafrost warming and water’s role

Short-term warming can sometimes boost carbon sinks in alpine permafrost, but longer warming strips those benefits away, leaving weakened soils and rising emissions.

In the Arctic, extended warming allows plants to thrive and strengthen carbon uptake, even as methane and nitrous oxide seep out of thawing layers.

Soil moisture plays the deciding role: dry soils release carbon dioxide but absorb methane, while wet soils lock in more carbon through plants yet pump out methane and nitrous oxide.

Small changes in water balance can shift entire regions from sink to source – and on a warming planet, those shifts will only grow sharper.

Abrupt thaw unlocks hidden carbon

Gradual warming is not the only risk. Abrupt thaw events, like landslides or ground collapse, can suddenly expose deep carbon layers in permafrost. Such events may strike less than a fifth of permafrost regions but could release almost half the stored carbon.

Wildfires add another blow. Flames clear vegetation, deepen permafrost thaw, and spark microbes that release greenhouse gases.

“Keeping additional warming below 2°C (3.6°F) in permafrost regions can help avoid a widespread positive permafrost–climate feedback in general,” said Xu Xiyan, corresponding author of the study.

“However, measures to mitigate warming in alpine permafrost ecosystems are urgent to preserve their fragile carbon sink.”

Future warming hinges on permafrost

The Intergovernmental Panel on Climate Change lists permafrost feedbacks as a major unknown in global carbon budgets. “We aim to uncover the patterns and mechanisms of greenhouse gas responses to warming in permafrost ecosystems, providing crucial data for improving climate projections,” said co-author Jia Gensuo.

Yet gaps remain. Most experiments simulate modest warming, not the much higher levels the Arctic is already facing.

Many studies track only summer months, ignoring autumn and spring, when microbes remain active and can release large amounts of methane. Abrupt permafrost thaw and wildfire effects are also underrepresented in experiments.

To prepare for the future, scientists argue for year-round fieldwork, more extreme warming tests, and closer study of fragile alpine systems. The frozen north is no longer silent. Its response will shape how fast the world warms, and how much harder the fight against climate change becomes.

The study is published in the journal Science Advances.

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