On average, every additional degree of land warming leads to wetland methane emissions increase by approximately 24 million tons per year, and under a severe global warming scenario, emissions might rise by 50–60% by the 2090s compared to the 2010s levels. This conclusion was drawn by an international team of the researchers from the U.S. National Oceanic and Atmospheric administration, the Lawrence Laboratory, the UK Met Office, and the other research centers led by the scientists from the Chinese Academy of Sciences. In the largest study to date on global warming impact on methane emissions from wetlands, the scientists used seven state-of-the-art Earth biosphere models and the climate scenarios with high levels of warming. This has significantly reduced the uncertainty of predictions about how much wetlands will amplify the greenhouse effect in the 21st century.
Until now, the estimates of future wetland methane emissions have varied widely, ranging from 20% to 250% increase by 2100. Such a wide range made it extremely difficult to account for this natural factor in international climate projections.
To make their estimates more accurate, the scientists decided to investigate whether the current wetland response to warming is related to how much methane emissions would rise in the future. For this, they used data from long-term observations in 42 wetland areas around the world. Measurements were made using the eddy covariance method allowing direct tracking of how much gas the surface releases into the atmosphere.
Based on this data, the researchers calculated the temperature sensitivity of the wetlands: how much methane emissions increase as the average temperature rises. It turned out that the models in which wetlands are already much stronger reacting to warming today, also show a sharper increase in emissions by the end of the century. Thanks to this, scientists were able to compare climate models with actual observations and make significantly more reliable predictions.
After applying this approach, the range of forecasts narrowed by more than half – by 53%. The updated estimates show that global methane emissions from wetlands will increase by 50–60% by the 2090s compared to 2010 levels, reaching an average of about 352 million tons per year.
The largest increase in emissions is expected in the tropics – the Amazon, the Congo Basin, the Pantanal wetlands, and the Ganges Delta – where high temperatures and rising CO₂ concentrations most strongly stimulate vegetation growth. As a result, waterlogged soils accumulate more organics which feeds methane-producing microorganisms. The Tibetan Plateau produced unexpected results as well. According to scientists’ calculations, by the end of the century it could become a major new source of methane and, in terms of emission volume, even surpass the well-known northern wetlands of Western Siberia and the Hudson Bay region.
The most alarming finding of the study concerns the coming decades. Scientists estimate that by the 2030s, additional methane emissions from wetlands due to warming, with a 90% probability, will amount to about 10 million tons per year, which is equivalent to 8–10% of the volume of anthropogenic methane emissions that countries plan to reduce under the international Global Methane Pledge initiative.
So, nature itself could negate nearly one-tenth of human efforts to reduce methane emissions. Moreover, in the worst-case scenario, wetland emissions could offset as much as one-third of the planned reductions.
In Russia, active research into the role of Siberian wetlands in global climate change revealed that the key factors making an impact on methane emissions and carbon sequestration by Russian wetlands are seasonal climate fluctuations, as well as the degree of openness and forest cover.
“Different types of wetland ecosystems sequester between 40 and 110 g of carbon per square meter per year. However, this figure varies significantly from year to year due to weather conditions variability: temperature, groundwater levels, and precipitation,” says in an interview with Global Energy Elena Lapshina, Head of the UNESCO Scientific and Educational Center-Department Environmental Dynamics and Global Climate Change, D.Sc. in Biology, Professor.
“So, an annual net carbon dioxide uptake varies depending on the bog type: a ridge-hollow complex absorbs 109 g of carbon per m² per year, which is approximately 20% more than in a forested pine-sphagnum bog, where it is 87.6 g of carbon per m² per year,” E. Lapshina said in addition to this.
At the same time, these ecosystems are an important source of methane. According to the expert, the intensity of methane emissions varies significantly among bog types. “In forested bogs (pine-shrub-sphagnum bogs), the annual methane emissions are 2–3 g of methane per m² per year and in waterlogged open areas, they are significantly higher, reaching 10–13 g m²/year. In this way, methane emissions in a forested bog are approximately two to three times lower than in an open waterlogged complex,” she noted.
At the same time, being a universal driver, solar radiation exerts the strongest influence on sensible heat fluxes and net CO₂ exchange. Air temperature acts as the main regulator of methane emissions and latent heat flux associated with evaporation. “Energy fluxes are intertwined with each other and gas fluxes: for example, an increase in latent heat flux correlates with an increase in methane emissions,” clarifies E. Lapshina.
According to her, the Western Siberia wetlands play a key role in the global carbon cycle, serving both as a long-term reservoir of organic matter in the form of peat and a significant source of methane. Therefore, their study is essential for understanding the future climate change.
