Alaskan Tundra Becoming Source of Seasonal Carbon Emissions

The amount of carbon dioxide being released from northern Alaska tundra during early winter has increased 70 percent since 1975, according to a new analysis by a team of scientists funded by NOAA and NASA and including CIRES.

The fate of carbon locked in northern permafrost—vast regions of frozen soil containing undecayed vegetation—is of intense interest to scientists. That’s because these soils contain an estimated 1,330-1,580 billion tons of organic carbon, about twice as much as currently contained in the atmosphere.

When permafrost thaws, carbon can be released to the atmosphere either as methane or carbon dioxide (CO2), both greenhouse gases. Scientists are concerned that increasing greenhouse gas emissions will accelerate a warming trend that could drive a further increase in greenhouse gas emissions from tundra.

Climate models used in recent climate assessments do not show the early winter carbon release in Arctic tundra regions.

Warmer fall temperatures observed in northern Alaska delay freezing of tundra, increasing the length of time the tundra gives off greenhouse gases, said the study’s lead author Róisín Commane of Harvard University. 

“In the past, tundra soils may have taken a month or so to freeze, but with warmer temperatures in recent years there are locations in Alaska where tundra soils now take more than three months to freeze completely,” Commane said. “We are seeing emissions of carbon dioxide from soils continue all the way through this early winter period."

Results of the study were published in last month’s Proceedings of the National Academy of Sciences.

The new study relied on measurements of CO2 made in 2012-2015 by instrumented aircraft that were part of the Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE). Longer-term changes in emissions on the North Slope were estimated by analyzing a 41-year record of CO2 measured at NOAA’s Barrow Atmospheric Baseline Observatory.

Barrow been warming about twice as fast as the rest of the North Slope, and offers a potential preview of how other northern tundra regions could respond to increased warming in the future, said co-author Colm Sweeney.

In 2016, Sweeney, a CIRES scientist working at NOAA, published research analyzing NOAA’s Barrow database and found that warming in the North Slope was not coincident with large emissions of carbon as methane, as some scientists had predicted.

“It wasn’t showing up as methane,” Sweeney said. “It is showing up as carbon dioxide.

“This new research demonstrates the critical importance of long-term monitoring to identify feedback mechanisms, which may amplify the unprecedented warming we are seeing throughout the Arctic,” he added.  

Commane, Sweeney and their colleagues are extending their research on Arctic carbon dioxide with the new NASA's Arctic-Boreal Vulnerability Experiment (ABoVE) project, which is in the second of five field seasons in Alaska and northwest Canada.