During the 2020 heatwave in Siberia, thawing permafrost released methane emissions from deep limestone deposits that date back hundreds of millions of years, according to a new study.
A team of geologists at the University of Bonn set out to investigate the effects of the 2020 heatwave by comparing the spatial and temporal distribution of methane concentrations in the air across northern Siberia.
The researchers found that increased methane levels after the heat wave were linked to limestone formations dating back to the Paleozoic era – from about 541 million to 251 million years ago.
Frozen permafrost soil covers large areas of the northern hemisphere. The permafrost will continue to thaw as temperatures rise, releasing CO2 and methane emissions that will amplify the greenhouse gas effect and drive further warming.
“Methane is particularly dangerous here because its warming potential is many times higher than that of CO2,” explained Dr. Nikolaus Froitzheim.
Previous studies have predicted that greenhouse gas emissions from thawing permafrost will only contribute about 0.2 degrees Celsius to global warming during this century. The new research suggests that the current calculations of greenhouse gas emissions associated with thawing permafrost are highly underestimated.
While previous research only accounted for emissions from the decay of organic matter in the permafrost soil, the current study looks at methane concentrations in the air.
Using satellite-based spectroscopy and geological maps, the team found significantly elevated methane concentrations in two areas of northern Siberia – the Taymyr Fold Belt and the rim of the Siberian Platform. In these regions, limestone formations are up to 541 million years old.
The elevated concentrations in these two areas appeared during the extreme heatwave in summer 2020 and persisted for months after. Next, the experts needed to determine the source of the methane.
“The soil formations in the observed areas are very thin to nonexistent, making methane emission from the decay of organic soil matter unlikely,” said Dr. Froitzheim.
The researchers propose that fracture and cave systems in the limestone, which had been clogged by a mixture of ice and gas hydrate, became permeable upon warming.
“As a result, natural gas being mainly methane from reservoirs within and below the permafrost can reach the Earth’s surface,” explained Dr. Froitzheim.
“The estimated amounts of natural gas in the subsurface of North Siberia are huge. When parts of this will be added to the atmosphere upon thawing of the permafrost, this could have dramatic impacts on the already overheated global climate.”
The study is published in the journal Proceedings of the National Academy of Sciences (PNAS).