How methane bubbles in Siberian lakes pose a threat to the global climate

By Megan Wilson

Gas bubbles that have been taking shape for the past forty thousand years are rising to the surface of melting Siberian glacier lakes at higher rates than ever before, researchers say.

The bubbles release powerful greenhouse gases into the Earth’s atmosphere and contribute to global warming, according to a recently published study.

The bubbles contain methane, a trace gas that has a “20-fold greater heating impact compared to carbon dioxide,” says an author of the new study recently published in the science journal Nature.  The methane from these bubbles is entering the atmosphere at higher rates than scientists expected.

Past research has shown that the size of the thaw lakes has increased by 14.7 percent since the 1970s because of melting permafrost ice.  This has led to a nearly 58 percent increase in emissions due to bubbling from the lake bottoms – a figure that is five times greater than what was previously estimated, according to Terry Chapin, a professor of ecology at the University of Alaska at Fairbanks.

“This makes it increasingly likely that the climate will warm even faster in the future,” Chapin said and Sergey Zimov, an author of the research has witnessed these changes first-hand.

In Northern Siberia, where Zimov has lived most of his life, the summers are usually dry and sunny, he said.  This summer, however, it has rained almost every day and has been much warmer, inviting a new pest: mosquitoes.  He has been living with and measuring these changes for the past 10 years.

  “It’s impossible to live here and not hear about these lakes,” he said in a telephone interview from his Siberian home in Cherskii. Even children are aware of what is happening because it is a longtime tradition to visit the lakes in Cherskii, he and Chapin said, and adults and children alike see how they have changed.

Zimov has measured the increase in area of these lakes through satellite photography. This increase in size is directly related to the increased methane emissions.

Inspired by Zimov’s observations, Katey Walter, the lead author of the study, is now the first person to quantify the actual ebullition, or bubbling, of greenhouse gases to the surface of these lakes over a continuous period, said Chapin. 

The gas making up these bubbles is mostly methane. It is created during the anaerobic decomposition, or decomposition in the absence of oxygen, of organic material contained in permafrost — soil from the soil that has been frozen since the Pleistocene Ice Age.  Ice makes up over 50 percent of the permafrost volume in Northern Siberia, and prevents oxygen from reaching the permafrost.

Once the permafrost thaws, microorganisms that decompose the soil would release carbon dioxide if oxygen were present.  Instead, they give off methane, a much more potent greenhouse gas, Chapin said.  For each cubic meter of Pleistocene soil, microorganisms produce 100 liters of methane, according to Zimov.

As the permafrost erodes, ice melts and leaves depressions and bubbles in the soil. Water flows flow into depressions above ground, according to Zimov and Chapin.  The bubbles in the soil then fill with methane gas, which is now making its way out as organic material decomposes at the anaerobic bottoms of lakes.

Walter and other authors measured bubbles frozen into the ice that formed on the lake surfaces in early winter by splitting two thaw lakes, out of 60,  into transects. They placed plastic umbrellas along transects to trap the bubbles.

“The science here is very solid,” said Stephen T. Gray, Wyoming State Climatologist.  Walter’s techniques have helped to predict the alarming amount of methane being released from all 60 thaw lakes in the area by recording bubble patterns in just two of the lakes.                           

Ninety percent of methane is released through ebullition, Chapin said.  There are three sources of ebullition: hot spots where the lake never freezes over and continuously emits methane bubbles, point sources where bubbles are regular but not nearly as frequent, and background ebullition where bubbling occurs episodically. 

The other 10 percent is released by simple diffusion from the water and ground, according to Chapin.     

Methane bubbling and diffusion is most prominent on the expanding edges of the lakes, Zimov said. Once methane leaves these lakes, it becomes a part of the global atmosphere almost instantly.

“I think in the end, we should be looking at what’s happening in these high-latitude areas,” Gray said in considering the future of global warming. “There is so much carbon and trace gases that it’s hard to wrap our brains around.”

The particular area in Siberia is “close to the latitudinal tree line, so it is a mix of tundra, forests and thaw lakes,” Chapin said and the larger the lakes in Cherskii grow, the more greenhouse gases will bubble from the permafrost below, further contributing to global warming. 

At the same time, more trees will likely begin to fill in the former tundra landscape, supplying more organic material for future decomposition and therefore greenhouse gases.      

Other places that will likely release methane in the future include reservoirs that were built over terrestrial landscapes, beaver ponds, and farm ponds, all of which would have a surplus of decomposable organic material at the bottom.  These can be anywhere, even in the United States, Chapin said.

Being able to account for this large source of methane in the global climate and discovering how to measure methane bubbling from different types of lakes will encourage closer examination of other landscapes that are potential threats for increased trace gas emissions, said Chapin.

Zimov has done research on the original ecosystems of Siberia and suggests reintroducing animals and plants that were eradicated by humans to the landscape, including bison, to help stabilize and even reverse the results of local climate change.

In high latitude areas, grazing animals would maintain vegetation year-round. “All the while they fueled plant productivity by fertilizing the soil with their manure, and they trampled down moss and shrubs, preventing these plants from gaining a foothold,” Zimov wrote in his article, published in Science. And by eating the plants that grew in the summer, they would prevent against excessive decomposition during cold months This all reduces future greenhouse gas emissions.

Converting the methane into energy is another option, Gray said. But, the increasingly marshy landscape would make that very difficult.  Definite solutions, immediate impacts, and future methane emission predictions are all outside scientists’ and climatologists’ reach.

“It really points out some of the subtle things about climate change that we don’t understand,” said Gray.  Walter and her colleagues have discovered an unaccounted for source of greenhouse gases, he says, and have proven that the source is very old.