Arctic lakes may contribute to global warming more than previously thought

Researchers at UiT the Arctic University of Norway report that warmer Arctic lakes give off more methane, a greenhouse gas. They examined ten lakes, some on Svalbard and some in northern Scandinavia. They found that even a slight rise in temperature speeds up the growth of algae and of plants near the water. According to the team, the extra vegetation raises methane production in the lake sediments. Sediments are layers of mud and organic matter that build up over time.

Experts at iC3, the Centre for Ice, Cryosphere, Carbon and Climate, point out that methane warms the atmosphere more than 25 times as strongly as carbon dioxide does. Arctic lakes were already recognised as one of the largest natural methane sources worldwide. The new study adds detail on how the gas forms in sediments and how it escapes.

The largest methane output came from sediments in shallower lakes and in lakes with more algae. PhD candidate Marie Bulínová said the team had not expected the ecosystem's productivity to track methane production so closely. She said the results indicate that warmer and wetter conditions raise biological productivity in Arctic lakes. She said this in turn pushes up methane emissions from the sediments.

The researchers also set their results beside figures from more than 60 lakes around the globe. Arctic lakes generally release less methane than lakes in warmer parts of the world. Even so, the study describes their emissions as substantial and very variable, because the north has so many lakes.

Bulínová added that the lakes in the study differ a great deal from one another. Some emit far more methane than others. The reasons include local factors: how much vegetation surrounds the lake, the shape of the basin, and what the sediment is made of.