Methane is a potent greenhouse gas, and much of it is trapped in permafrost, that is, permanently frozen ground in regions of arctic and subarctic tundra, where sub-zero temperatures prevail year-round. Rising temperatures are expected to thaw these frozen soils, leading to the release of large amounts of methane. This, in turn, will further boost the climate change.
That’s the bad news. The good news is that, according to new research from scientists in Sweden, the amount of methane released by thawing may be only a tenth of the amount previously predicted as a result of changes in hydrology, plant diversity, and microbial composition in the soil afterward. of frozen. thawed.
A team of researchers from various institutions across the Scandinavian nation measured methane release from two areas in northern Sweden: an area where permafrost disappeared in the 1980s and another where it disappeared 10 to 15 years later. His goal in doing this was to see what happens, how a landscape adapts to the absence of permafrost over time, and how changes affect the release of methane from the ground.
“The results show that the first area that lost its permafrost now has ten times lower methane emissions than the other site. This is due to gradual changes in drainage and the spread of new plant species”, report the scientists, who published your discoveries in the magazine Biology of Global Change .
The key to the new study
The main reason for the significant reduction in methane release in the affected areas is that with the disappearance of the permafrost, the water previously stored in the soil at the surface begins to drain.
“Permafrost acts like the bottom of a bathtub. When it melts, it’s as if the plug has been removed, allowing water to seep into the now-thawed ground. Drainage allows new plant species to establish themselves, plants that are better adapted to drier soil conditions. This is exactly what we are seeing in these places in Sweden,” explains Prof. Bo Elberling, a scientist at the University of Copenhagen’s Permafrost Center.
Another factor is the disappearance of grasses especially adapted to wetlands with sporadic permafrost. These plants have a straw-like system for transporting oxygen from their stems to their roots, and the straws also act as a conduit for methane from the soil that reaches the surface and from there to the atmosphere, scientists say.
However, when water disappears from the soil, these grasses are no longer able to thrive and are replaced by other plant species better adapted to dry soil conditions. “The combination of more oxygen in the soil and reduced transport of methane means that less methane is produced and that the methane produced can be better converted to CO2 within the soil,” the scientists note.
“As grasses are overtaken by new plants such as dwarf shrubs, willows and birch, the transport mechanism breaks down, allowing methane to quickly escape through the soil and into the atmosphere,” adds Elberling.
Also, drier soil with new plants growing in it creates more favorable conditions for soil bacteria that help break down methane. “When methane can no longer escape through the straws [de los pastos]Soil bacteria have more time to break it down and convert it to CO2,” says Elberling.
Neither methane nor CO2
However, this does not mean that this excess CO2 is released into the atmosphere and therefore causes climate change. But even if much of this CO2 escapes into the atmosphere, it is preferable to release methane in large quantities. “Critically, although methane ends up as CO2, it is considered less critical in the context of climate change, as methane is at least a 25% more potent greenhouse gas compared to CO2,” the scientists note.
There is still an unknown factor, which is how climate change will affect precipitation in the affected areas. While permafrost thawing makes it easier for water to drain from the ground, increased rainfall or poor drainage in a given area can prevent it from drying out. If this happens, a lot of methane will be released from the ground.
“The balance between precipitation and evaporation will be crucial for the release and absorption of greenhouse gases. However, the forecast for Arctic rains is fraught with uncertainty. In some areas we are seeing an increase in precipitation, while in others things are drying up, especially in the summer,” says Elberling.
Scientists also warn that more research will be needed to determine how areas with similar permafrost in countries like Canada and Russia will be affected by thawing in the coming years and decades. That said, the new research should lead to rethinking our view of tundra methane emissions in the face of a changing climate, say the scientists involved.
“In its most recent report on the future Arctic methane budget, the IPCC (Intergovernmental Panel on Climate Change) did not consider the conditions highlighted by us in the study. Our study reverses the general perception that thawing permafrost is consistently associated with higher levels of methane release,” says Elberling.
By Daniel T. Cross. Article in English