Higher estimates of methane emissions from melting permafrost could accelerate climate ‘tipping points’, says report
By Gerard Wynn
Thawing permafrost in the northern hemisphere will lead to relatively more methane than carbon dioxide emissions, which could lead to more serious climate impacts than previously thought, a study said.
Thawing peatland emits CO2 and methane, as new plants grow and microbes digest the newly available organic matter.
Whether they emit proportionally more methane or CO2 is important, because methane is more than 30 times more powerful as a greenhouse gas on a 100-year timescale.
Thawing permafrost could lead to significant greenhouse gas emissions, creating an unstoppable momentum, where emissions led to more warming in turn accelerating the thaw, in a series of positive feedbacks also called a tipping point.
Northern peatlands are already a net source of methane emissions, a powerful greenhouse gas, equivalent to 6–12% of annual fossil fuel emissions of CO2, estimated the new study published in the U.S. Proceedings of the National Academy of Sciences.
The authors tested the process of methane emissions from thawing permafrost at a site in northern Sweden.
They calculated that, as permafrost thawed, a gradual subsidence and flooding led to relatively more emissions of methane than CO2, as a result of a shift in chemical reactions as the peat thawed and flooded, and as different plant communities flourished.
“This impact of permafrost thaw on organic matter chemistry could intensify the predicted climate feedbacks,” said the authors from various US and European universities and research centres, describing previous estimates as “conservative” in the light of the new findings.
A continuing permafrost thaw, and especially rising methane emissions, can have potentially significant climate impacts.
Peatlands in the permafrost zone of the northern hemisphere contain an estimated 277 billion tonnes of carbon, equivalent to 1,017 billion tonnes of carbon dioxide (CO2), the paper reported.
That compares with annual manmade carbon dioxide emissions from burning fossil fuels of 34.5 billion tonnes of CO2.
And it is roughly equal to the 1 trillion tonnes of CO2 that humankind can emit over the course of this century and still limit global average warming to no more than 2C, which is deemed a level that will avoid the most dangerous floods, droughts and short-term sea level rise.