In an area of Alaska, an unusual proliferation of methane leaks has recently been recorded at specific natural points in the subsoil. Methane is a gas with a more powerful greenhouse effect than carbon dioxide. A recent study investigated why methane is more likely to escape into the atmosphere from these locations than from others.
Natural methane emission “hot spots” in Alaska were first observed in 2017, using NASA’s next-generation spectrometer, the AVIRIS-NG (Airborne Visible/Infrared Imaging Spectrometer). Installed in the belly of a research plane, the instrument captures the interaction of sunlight with molecules located near the Earth’s surface, in the air, and has been used to measure and monitor dangerous phenomena ranging from oil spills to pests in agricultural fields.
About two million methane hot spots (defined as areas showing an excess of 3,000 parts per million of methane between the plane and the ground) were detected in about 30,000 square kilometers of Arctic territory. Regionally, the number of hot spot detections in the Yukon and Kuskokwim River Delta was abnormally high during surveys in 2018, with no cause identified.
The team led by Elizabeth Yoseph, from NASA’s Goddard Space Flight Center in the United States, focused on a region with high methane emissions located in a muddy area of the enormous delta. Yoseph and her colleagues used AVIRIS-NG data to locate hot spots across more than 1,780 square kilometers, and then, out of suspicion, compared the hot spot map to a map of recent large wildfires.
The bubbles emerging from the water of this Alaskan lake are methane. The lake is one of the sites monitored for its methane emissions. (Photo: NASA / Kate Ramsayer)
The comparison has revealed that there is a very clear and close relationship between fire history and the distribution of methane hot spots.
The relationship arises from what happens when fire burns away the carbon-rich frozen soil, or permafrost, underlying the tundra. Permafrost (a mixture of ice and other materials) traps carbon from the atmosphere and can keep it stored for tens of thousands of years. But when it thaws and decomposes in humid areas, there are microbes that feed on that old carbon and convert it into methane gas. Saturated soils around lakes and wetlands in general tend to be especially rich carbon reserves because they contain large amounts of dead vegetation and organic matter in general.
Methane “hot spots” in the Yukon and Kuskokwim river delta are primarily where recent wildfires have scorched the tundra.
In a vicious cycle, this release of methane can in turn accelerate global warming and fuel more wildfires in permafrost-rich tundra areas, where fires have historically been very rare.
Unfortunately, such fires will become more frequent due to global warming. According to some projections, the risk of fire in the Yukon and Kuskokwim River Delta area could increase four-fold by the end of this century due to rising temperatures and an increase in lightning storms. Whether or not these forecasts will be fulfilled, no one can know with certainty, but for now two of the largest fires in the Alaskan tundra of all those documented with sufficient rigor occurred last year, and more than a hundred burned in them. thousand hectares.
To what extent can emissions from Arctic permafrost influence the global climate? We can get an idea if we consider that the Arctic permafrost is estimated to host 1.7 trillion tons of carbon, approximately 51 times the carbon emitted into the atmosphere from the burning of fossil fuels in 2019.
The study is titled “Tundra fire increases the likelihood of methane hotspot formation in the Yukon–Kuskokwim Delta, Alaska, USA.” And it has been published in the academic journal Environmental Research Letters. (Source: NCYT from Amazings)
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