Do we have to expect another self-reinforcing effect of climate change? Last year, the hot summer in Siberia not only released greenhouse gases from the biomass of the thawing soil, but also probably mobilized methane from limestone formations, researchers report. This emerges from spatial and temporal comparisons of methane concentrations in the air in Northern Siberia with geological maps. Further investigations are now intended to further explore the significance of this potential danger for the development of the global climate.
Many studies in recent years have shown that global warming is particularly noticeable in the northern latitudes of our planet. In addition to the continuous increase in the annual average values, more frequent extreme events are also to be expected. An example of this was apparently the summer of 2020 in Siberia: The temperatures reached values that were well above the long-term peak temperatures. For climate researchers, the question arises as to how this has affected the release of greenhouse gases from the thawing permafrost in the region. Because the so-called permafrost greenhouse gas climate feedback is a critical factor in the further development of human-induced global warming.
Self-reinforcing greenhouse effect
Due to the loss of the stabilizing effect of the ice, the effect of the thawing of the permafrost is already clearly visible in many places: the soil is losing its hold and the landscape is changing. Due to the lack of a “freezer effect”, the biomass stored in the soil is available for decomposition by microorganisms. During this biological degradation process, they release carbon dioxide and the much stronger greenhouse gas methane. “Methane only occurs in low concentrations, but it is particularly dangerous because its warming potential is many times higher than that of CO2,” explains Nikolaus Froitzheim from the University of Bonn. Most previous projections, however, have shown that the greenhouse gases from thawing permafrost will contribute “only” about 0.2 degrees Celsius to global warming by 2100.
The results of Froitzheim and his colleagues now call this assumption into question. In previous studies, scientists have mostly dealt exclusively with the emissions that arise from the decomposition of the biomass in the permafrost soil itself. As part of their study, however, the team chose an investigation strategy that enables a large-scale overview: Using satellite-based spectroscopy, they recorded the methane concentrations in the Siberian air in the summer of 2020. They then compared the data obtained with maps of the region, which provided information about the condition emerge from the subsurface.
As they report, the evaluations of the satellite data in two areas of northern Siberia revealed astonishingly high concentrations of methane, which were apparently caused by the high summer temperatures. It was the Taymyr fold belt and the edge of the Siberian platform. According to the scientists, these two elongated areas have two geological peculiarities: The ground is only thinly covered by biomass layers and the subsoil is characterized by limestone formations from the Paleozoic, which were formed around 541 to around 251.9 million years ago. So the question arose: Why did so much methane rise from the ground there, of all places?
A danger in sight
“The soils in the observed areas are very thin or completely absent, which makes the decomposition of organic matter as a source of methane unlikely,” says Froitzheim. In addition, the increased methane concentration was evident for months after the heat in the region, according to the results. As the scientists explain, a non-biological source for the methane is therefore obvious: They fear that, as a result of the warming, fractures and cave systems in the limestone previously filled with ice and gas hydrate have become permeable. “As a result, natural gas, which consists mainly of methane, found its way to the surface of the earth from deposits in the permafrost and below the permafrost,” explains Froitzheim.
However, as he and his colleagues point out, more research is needed to confirm this explanation. Using on-site measurements and model calculations, they now want to investigate whether, how quickly and to what extent ground warming could have released natural gas in the region. In conclusion, Froitzheim says: “The amounts of natural gas that are suspected to be underground in Northern Siberia are enormous. If parts of it were released into the atmosphere through the thawing permafrost, this could have a dramatic impact on the earth’s already overheated climate, ”says the scientist.
Source: Rheinische Friedrich-Wilhelms-Universität Bonn, specialist article: PNAS, doi: 10.1073 / pnas.2107632118