The Arctic is warming at an accelerating pace. As permafrost thaws across vast areas and wildfires become more frequent, large amounts of methane (CH4) are being released. Together, these changes are reshaping the region's greenhouse-gas emissions and further intensifying climate change.
In a study published in Science on August 6, an international team led by Prof. LIU Yi from the Institute of Atmospheric Physics (IAP) of the Chinese Academy of Sciences investigated how CH4 emissions in Siberia are evolving under climate change, showing how atmospheric circulation promotes wildfire activity and methanogenesis and thereby drives the recent sharp rise in CH4 emissions.
Although Siberia accounts for only ~5% of global CH4 emissions, sparse observations and complex environmental conditions have made its emissions difficult to quantify, resulting in widely varied estimates. Under these conditions, researchers have long struggled to understand changes in the region's emissions and the role played by temperature, making Siberia an important source of uncertainty in the global CH4 budget.
Using a methane flux inversion system developed by Dr. ZHU Sihong from IAP, first author of this study, researchers integrated measurements from the Greenhouse Gases Observing Satellite (GOSAT) with data from a global network of near-surface monitoring stations, including tall-tower observations in Siberia. This approach reduced uncertainties in estimates of both Siberian CH4 emissions and their growth trend to roughly 10%.
Researchers found that annual CH4 emissions in Siberia rose by 12.0 ± 1.9 teragrams (Tg) between 2010 and 2023, increasing by an average of 1.1 ± 0.1 Tg each year. Notably, this rate of increase was equivalent to 92% of the increase in emissions from wetlands worldwide, which account for nearly one-third of global CH4 emissions.
"We first detected the upward trend in Siberian CH4 emissions in 2021," Prof. LIU said. Rather than draw a conclusion, the researchers raised two questions: "How could we independently validate a finding derived from satellite remote sensing? And what physical mechanisms were driving the Siberian CH4 emission increase?"
The researchers then spent several years on a two-pronged verification effort. First, they tested the result against multiple observational data sets and independent methods. Second, they examined the atmospheric processes that connect climate change to methane emissions.
The researchers found that the Yenisei River marks a divide between two emerging climate regimes: Western Siberia is becoming wetter, while eastern Siberia is becoming warmer and drier. The mechanisms driving the growth in CH4 emissions differ sharply between the two regions.
In western Siberia, the dominant influence is the wintertime Scandinavian pattern of atmospheric circulation. Stronger transport of heat and moisture warms the land surface and alters the thermal and hydrological conditions of permafrost and wetland ecosystems. Those changes favor methanogenesis and CH4 release, causing emissions to rise at a rate of 0.4 ± 0.1 Tg CH4 yr-2.
In eastern Siberia, the increase is more closely associated with Arctic Oscillation-related high-pressure anomalies. Persistent warm and dry conditions under these systems raise the likelihood that wildfires will ignite and spread, boosting fire-related CH4 emissions at a rate of 0.7 ± 0.1 Tg CH4 yr-2.
Moreover, researchers found that CH4 emissions exhibited an accelerating, weakly nonlinear response to temperature maxima. Employing an emergent constraint approach—which uses real-world observations to refine climate-model projections—they narrowed the uncertainty in model projections of regional warming.
Under the high-emissions SSP5-8.5 scenario, the projected increase of Siberian CH4 emissions in 2050, relative to the 2010–2023 mean, would be comparable to the anticipated rise in global wetland methane emissions and could offset about 20% of the anthropogenic methane reductions required to meet climate targets. Eastern Siberia is projected to account for most of this increase.
"If we ignore these regional, nonlinear feedbacks, estimates of the global methane budget could be seriously biased. Changes in natural sources could also offset part of our mitigation efforts," Prof. LIU said. "Global climate assessments therefore need to account for such 'overshoot' effects and adopt more conservative assumptions about the future."
The study quantitatively identifies the mechanisms driving rising CH4 emissions from Siberian permafrost regions under rapid Arctic warming, providing scientific evidence for global methane-mitigation policies and research into regional climate thresholds. It is another advance by Prof. LIU's team in understanding greenhouse-gas budgets and their climate and environmental effects, following its 2020 Nature study quantifying greenhouse-gas sources and sinks.
