Carbon emissions from Alaskan tundra higher by 70 percent since 1975

Emissions of carbon dioxide from Alaskan tundra to the atmosphere have increased by 70 percent in the past 42 years, a new study shows. The reason has to do with warmer temperatures recorded over the years and thawing soils. Researchers say that more carbon dioxide released to the atmosphere will accelerate climate warming, which, in turn, might lead to even more CO2 being released from the soil.

NASA and the National Oceanic and Atmospheric Administration (NOAA) supported a study led by Roisin Commane, an atmospheric researcher at Harvard University in Cambridge, Massachusetts. The paper found that the amount of carbon dioxide emitted from northern tundra areas between October and December each year has increased 70 percent since 1975.

Three years of aircraft observations from NASA’s Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE) airborne mission were analysed to estimate the spatial and seasonal distribution of Alaska’s carbon dioxide emissions. Researchers also looked at NOAA’s 41-year record of carbon dioxide measured from ground towers in Alaska.

According to the study, cited in a press release, the soils that encircle the high northern reaches of the Arctic (above 60 degrees North latitude) hold vast amounts of carbon in the form of undecayed organic matter from dead vegetation. This vast store, accumulated over thousands of years, contains enough carbon to double the current amount of carbon dioxide in Earth’s atmosphere.

During the Arctic summer, the upper layers of soil thaw and microbes decompose this organic matter, producing carbon dioxide. When cold temperatures return in October, the thawed soil layers begin to cool, but high rates of carbon dioxide emissions continue until the soil freezes completely.

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

By comparing simultaneous measurements of atmospheric carbon dioxide and carbon monoxide, Commane and her co-authors split apart their estimates of the total carbon budget of Alaska into contributions from the three major sources of atmospheric carbon: burning of fossil fuels by people; wildfires; and microbes decomposing organic matter in the soil. In sparsely populated Alaska, the soil microbes were a much bigger source of atmospheric carbon than fossil fuel burning. Wildfires were a big source of atmospheric carbon in just one year of the CARVE experiment, 2013.

“Tundra soils appear to be acting as an amplifier of climate change. We need to carefully monitor what it’s doing up there, even late in the year when everything looks frozen and dormant,” co-author Steve Wofsy, a Harvard atmospheric scientist, said.

Researchers plan to expand on this work with NASA’s Arctic-Boreal Vulnerability Experiment (ABoVE) field campaign, now in its second season in Alaska and northwest Canada. As part of the broader ABoVE effort, they will make airborne measurements of carbon dioxide and methane each month from April through October.