NASA scientists have contributed to a new study that reveals the Arctic’s permafrost region is releasing more greenhouse gases than it absorbs, exacerbating near-term global warming. The research, led by Stockholm University, found that from 2000 to 2020, carbon dioxide uptake by the land was largely offset by its emissions. Abhishek Chatterjee, a co-author and scientist at NASA’s Jet Propulsion Laboratory, notes that climate-driven changes are tipping the balance toward permafrost being a net source of greenhouse gas emissions.
The permafrost region stores twice as much carbon as currently resides in the atmosphere, with most of it buried for centuries. However, as the Arctic warms, microbes feed on thawing organic matter, releasing methane and carbon dioxide. NASA’s Arctic-Boreal Vulnerability Experiment (ABoVE) and satellites like the Orbiting Carbon Observatory-2 (OCO-2) were used to track emissions across the vast region. The study suggests that events like extreme wildfires and heat waves are major sources of uncertainty when projecting into the future, highlighting the complexity of the issue.
Thawing Permafrost: A Tipping Point for Global Warming
The Arctic region, spanning from Alaska to Canada to Siberia, is home to vast expanses of permafrost – ground that has been permanently frozen for anywhere from two years to hundreds of thousands of years. This frozen soil stores twice as much carbon as currently resides in the atmosphere, with most of it having been buried for centuries. However, new research suggests that this carbon stockpile is thawing at an alarming rate, releasing greenhouse gases and contributing to near-term global warming.
Carbon Stockpile
Permafrost is composed of thick layers of icy soils enriched with dead plant and animal matter that can be dated using radiocarbon and other techniques. When permafrost thaws and decomposes, microbes feed on this organic carbon, releasing some of it as greenhouse gases. Unlocking a fraction of the carbon stored in permafrost could further fuel climate change. Temperatures in the Arctic are already warming two to four times faster than the global average, and scientists are learning how thawing permafrost is shifting the region from being a net sink for greenhouse gases to becoming a net source of warming.
The Permafrost Tunnel north of Fairbanks, Alaska, has been a site of extensive research into permafrost. The tunnel, dug in the 1960s and run by the U.S. Army’s Cold Regions Research and Engineering Laboratory, provides a unique opportunity for scientists to study the composition and behavior of permafrost up close. Researchers have tracked emissions using ground-based instruments, aircraft, and satellites, including NASA’s Arctic-Boreal Vulnerability Experiment (ABoVE), which is focused on Alaska and western Canada.
Cracks in the Sink
The new study, undertaken as part of the Global Carbon Project’s RECCAP-2 effort, brings together different science teams, tools, and datasets to assess regional carbon balances every few years. The authors followed the trail of three greenhouse gases – carbon dioxide, methane, and nitrous oxide – across 7 million square miles (18 million square kilometers) of permafrost terrain from 2000 to 2020.
Researchers found that the region, especially the forests, took up a fraction more carbon dioxide than it released. This uptake was largely offset by carbon dioxide emitted from lakes and rivers, as well as from fires that burned both forest and tundra. They also found that the region’s lakes and wetlands were strong sources of methane during those two decades. Their waterlogged soils are low in oxygen while containing large volumes of dead vegetation and animal matter – ripe conditions for hungry microbes.
Bottom Up, Top Down
The scientists used two main strategies to tally greenhouse gas emissions from the region. “Bottom-up” methods estimate emissions from ground- and air-based measurements and ecosystem models. Top-down methods use atmospheric measurements taken directly from satellite sensors, including those on NASA’s Orbiting Carbon Observatory-2 (OCO-2) and JAXA’s (Japan Aerospace Exploration Agency) Greenhouse Gases Observing Satellite.
Regarding near-term, 20-year, global warming potential, both scientific approaches aligned on the big picture but differed in magnitude: The bottom-up calculations indicated significantly more warming. This study is one of the first where scientists are able to integrate different methods and datasets to put together a very comprehensive greenhouse gas budget into one report, revealing a complex picture.
The findings suggest that the net change in greenhouse gases helped warm the planet over the 20-year period. However, over a 100-year period, emissions and absorptions would mostly cancel each other out. In other words, the region teeters from carbon source to weak sink. The authors noted that events such as extreme wildfires and heat waves are major sources of uncertainty when projecting into the future.
The thawing of permafrost is a critical component in understanding global warming, and this study highlights the need for continued research and monitoring of greenhouse gas emissions from this region. As the Arctic continues to warm at an alarming rate, it is essential that scientists and policymakers work together to mitigate the effects of climate change.
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