”Bubbles from lakes are one of the largest transport paths for the greenhouse gas methane to move between the land and the atmosphere, but bubbles are also the hardest path to measure. By linking methane bubbling with incoming sunlight, we connect methane bubbling to something much easier to measure, and something we can use to estimate bubbling over longer periods of time—both in the past and in the future,” says Brett Thornton, a researcher at Stockholm University, who led the study recently published in Geophysical Research Letters.

The researchers have used predictions of how much of the year the lakes will be ice-free in the future, and then made calculations of how much methane will bubble from the lakes up to the year 2079.

”This result is important for making large-scale estimates of how much methane reaches the atmosphere from lakes in Sweden, and over the whole Arctic, no matter what the future temperatures are,” says Brett Thornton.

The research group at Stockholm University has studied lakes in Stordalen Mire, near Abisko in northern Sweden. These lakes are typical of those found in arctic and subarctic climates; they are relatively shallow and embedded in a peat and wetland landscape. The amount of methane released annually via bubbles in the studied lakes in Sweden has grown 24 percent since 1916. By 2079, the total predicted increase is 80 percent.

Last year the research group published work which combined data on methane bubbles with measurements of sunlight during each ice-free summer season. The results were surprising; the amount of methane bubbling from the lakes was strongly coupled to available sunlight.

With this new information, the researchers combined existing longer-term measurements of incoming sunlight in Abisko with information on when the lakes in the area became ice-free, and their own recent measurements of methane in bubbles. The results have allowed reliable back-estimates of methane bubbling from shallow lakes in northern Sweden as far back as 1916.

Facts on methane

Methane is an important greenhouse gas which, over long timescales of about a century, has a higher global warming potential than carbon dioxide. Researchers have cautioned that rising temperatures in the Arctic may release carbon that has long been stored in permafrost, and some of this carbon could eventually reach the atmosphere as methane. This potential release of carbon and methane from permafrost around the Arctic has attracted a large amount of scientific attention in recent years.

A research group led by Patrick Crill at Stockholm University’s Department of Geological Sciences has studied methane release from Stordalen Mire for several years. The group measures methane release from wetlands and several lakes in the mire.

Link to article in Geophysical Research Letters.