Winter sun setting over the tundra polygons in northern Alaska in November 2015. As winter sets in and snow settles, the soils take time to freeze completely and continue to emit carbon dioxide long into the new year. Photo: Charles Miller / NASA / JPL-Caltech

By Bob Berwin
8 May 2017

(InsideClimate News) – Soaring temperatures in the Arctic have triggered a huge seasonal surge in carbon dioxide emissions from thawing permafrost and may be tipping the region toward becoming a net source of heat-trapping greenhouse gases, a new study shows.

Even into early winter, when the ground would have been frozen 40 years ago, microbes in the permafrost are continuing to release heat-trapping greenhouse gases. Carbon dioxide emissions are now outpacing the uptake of CO2 during the spring and summer growing season, the study suggests.

The study's authors, researchers from Harvard, the National Oceanic and Atmospheric Administration and other institutions, measured atmospheric CO2 in Alaska and found that emissions from October through December have increased by 73 percent since 1975 and that the increase correlates with rising summer temperatures.

The findings suggest that global climate models are underestimating how much greenhouse gas pollution will be unleashed as the Arctic continues to warm at twice the global average rate, said lead author Roisin Commane of the Harvard School of Engineering and Applied Sciences.

The Arctic climate feedback loop is stronger than scientists estimated, Commane said. Global warming thaws permafrost, releasing more greenhouse gases, which causes yet more warming.

"It's consistent with the effects of a warming Arctic," she said. "We're seeing very large emissions in the early winter. When I looked at the models used by the IPCC [Intergovernmental Panel on Climate Change], none of them looked at the fall respiration. They didn't realize how important that is." [more]

Thawing Alaska Permafrost Sends Autumn CO2 Emissions Surging


By Ellen Gray
8 May 2017

(NASA) – Warmer temperatures and thawing soils may be driving an increase in emissions of carbon dioxide from Alaskan tundra to the atmosphere, particularly during the early winter, according to a new study supported by NASA and the National Oceanic and Atmospheric Administration (NOAA). More carbon dioxide released to the atmosphere will accelerate climate warming, which, in turn, could lead to the release of even more carbon dioxide from these soils.

A new paper led by Roisin Commane, an atmospheric researcher at Harvard University in Cambridge, Massachusetts, finds the amount of carbon dioxide emitted from northern tundra areas between October and December each year has increased 70 percent since 1975. Commane and colleagues analyzed three years of aircraft observations from NASA's Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE) airborne mission to estimate the spatial and seasonal distribution of Alaska's carbon dioxide emissions. They also studied NOAA's 41-year record of carbon dioxide measured from ground towers in Barrow (the name recently changed back to Utqiagvik), Alaska. The aircraft data provided unprecedented spatial information, while the ground data provided long-term measurements not available anywhere else in the Arctic. Results of the study are published today in the Proceedings of the National Academy of Sciences.

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," said Commane. "We are seeing emissions of carbon dioxide from soils continue all the way through this early winter period."

"Data from Barrow show steady increases of both atmospheric carbon dioxide and temperature in late fall and early winter," said co-author Colm Sweeney of the Cooperative Institute for Research in Environmental Sciences in Boulder, Colorado. "This new research demonstrates the critical importance of these long-term monitoring sites in verifying the subtle feedbacks, such as increases in carbon dioxide, which may amplify the unprecedented warming we are seeing throughout the Arctic."

CARVE flew an instrumented NASA aircraft to measure atmospheric carbon dioxide and other greenhouse gases over Alaska from April to November in 2012, 2013 and 2014. These data, along with satellite data on the vegetation status and ground data to provide a year-round context and a long-term record, gave the scientists a detailed picture of carbon emissions at the regional level.

"One of CARVE's main objectives was to challenge the idea that carbon dioxide respiration stopped as soon as the snow fell and the land surface froze," said Charles Miller, a scientist at NASA's Jet Propulsion Laboratory in Pasadena, California, and CARVE principal investigator. "The CARVE flights prove that microbial respiration continues in tundra soils months after the surface has frozen."

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," said co-author Steve Wofsy, a Harvard atmospheric scientist. "We need to carefully monitor what it's doing up there, even late in the year when everything looks frozen and dormant."

"The entire Alaska region is responding to climate change," said professor Donatella Zona of San Diego State University in California, who was not affiliated with the study. "Surface measurements suggest that the amount of carbon lost from Arctic ecosystems to the atmosphere in the fall might have been increasing over the past decades. By better capturing these cold season processes and putting previous smaller-scale measurements into a bigger context, this study will help scientists improve climate models and predictions of Arctic climate change."

Commane, Sweeney, Miller and their colleagues 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.

Contact

Alan Buis
Jet Propulsion Laboratory, Pasadena, California
818-354-0474
alan.buis@jpl.nasa.gov

Alaska tundra source of early-winter carbon emissions


ABSTRACT: High-latitude ecosystems have the capacity to release large amounts of carbon dioxide (CO2) to the atmosphere in response to increasing temperatures, representing a potentially significant positive feedback within the climate system. Here, we combine aircraft and tower observations of atmospheric CO2 with remote sensing data and meteorological products to derive temporally and spatially resolved year-round CO2 fluxes across Alaska during 2012–2014. We find that tundra ecosystems were a net source of CO2 to the atmosphere annually, with especially high rates of respiration during early winter (October through December). Long-term records at Barrow, AK, suggest that CO2 emission rates from North Slope tundra have increased during the October through December period by 73% ± 11% since 1975, and are correlated with rising summer temperatures. Together, these results imply increasing early winter respiration and net annual emission of CO2 in Alaska, in response to climate warming. Our results provide evidence that the decadal-scale increase in the amplitude of the CO2 seasonal cycle may be linked with increasing biogenic emissions in the Arctic, following the growing season. Early winter respiration was not well simulated by the Earth System Models used to forecast future carbon fluxes in recent climate assessments. Therefore, these assessments may underestimate the carbon release from Arctic soils in response to a warming climate.

SIGNIFICANCE: Rising arctic temperatures could mobilize reservoirs of soil organic carbon trapped in permafrost. We present the first quantitative evidence for large, regional-scale early winter respiration flux, which more than offsets carbon uptake in summer in the Arctic. Data from the National Oceanic and Atmospheric Administration’s Barrow station indicate that October through December emissions of CO2 from surrounding tundra increased by 73% since 1975, supporting the view that rising temperatures have made Arctic ecosystems a net source of CO2. It has been known for over 50 y that tundra soils remain unfrozen and biologically active in early winter, yet many Earth System Models do not correctly represent this phenomenon or the associated CO2 emissions, and hence they underestimate current, and likely future, CO2 emissions under climate change.

Carbon dioxide sources from Alaska driven by increasing early winter respiration from Arctic tundra

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