Thawing permafrost is becoming an enormous source of global warming

A few decades ago, it was established that the farthest corners of our planet had conserved carbon in frozen permafrost for many years. However, recent studies led by experts at NASA suggest that Arctic permafrost is approaching a tipping point.

As it thaws, the permafrost is releasing greenhouse gases like carbon dioxide and methane – both of which accelerate global warming.

Frozen Arctic permafrost

Permafrost is ground that remains permanently frozen, typically year-round, for extended periods – often spanning decades, centuries, or even millennia.

Found mostly in the Earth’s northern regions, such as the Arctic and parts of Alaska, Canada, and Siberia, permafrost serves as a natural storehouse of carbon.

This frozen ground traps organic matter like dead plants and animal remains that have not fully decomposed due to the low temperatures.

Underground carbon safe

Over time, these materials accumulate vast amounts of carbon, effectively locking it underground in what has long been considered a “carbon safe.”

However, as the Arctic warms at an accelerated rate – up to four times faster than other regions – permafrost begins to thaw. This thawing process releases previously stored greenhouse gases, particularly carbon dioxide and methane, into the atmosphere.

These heat-trapping gases contribute to global warming, turning permafrost from a carbon sink into a source of emissions.

Greenhouse gases released from permafrost

A recent study led by scientists at NASA and Stockholm University provides intriguing insights into this vast permafrost region.

The study meticulously accounts for where and how greenhouse gases are making their escape as the Arctic warms up.

The researchers discovered that, between 2000 and 2020, emissions from the land nearly overshadowed the carbon dioxide absorbed by it.

The permafrost region, thus, is increasingly contributing to global warming. This phenomenon is also linked to another greenhouse gas – methane. While not as long-lived as carbon dioxide, methane can pack quite a punch within its short lifetime, trapping heat much more effectively.

Tipping the balance of permafrost

Abhishek Chatterjee is a scientist at NASA’s Jet Propulsion Laboratory (JPL) in Southern California and a co-author of the study.

“We know that the permafrost region has captured and stored carbon for tens of thousands of years,” said Chatterjee.

“But what we are finding now is that climate-driven changes are tipping the balance toward permafrost being a net source of greenhouse gas emissions.”

Perhaps the concept of permafrost needs a bit more unpacking. A slice from the core of permafrost unveils layers upon layers of icy soils. These soils are chock-full of dead plant and animal matter, which can be carbon-dated using various techniques.

This is the organic carbon that microbes feed on when permafrost thaws and decomposes, expelling some of it as greenhouse gases.

Tracking permafrost emissions

Scientists have been using an array of methods to track emissions – from ground-based instruments and aircraft to satellites.

NASA’s Arctic-Boreal Vulnerability Experiment (ABoVE) zeroes in on Alaska and western Canada. However, taking measurements across the vast northern expanses is anything but straightforward.

The new study, part of the Global Carbon Project’s RECCAP-2 effort, monitored three greenhouse gases – carbon dioxide, methane, and nitrous oxide – across 7 million square miles of permafrost terrain from 2000 to 2020.

Carbon release across Arctic ecosystems

The experts found that forests absorbed slightly more carbon dioxide than they released. However, this was largely offset by carbon dioxide emissions from lakes and rivers as well as from forest and tundra fires.

The findings suggest that greenhouse gases contributed to planetary warming over the 20-year period. But over a 100-year timeframe, emissions and absorptions would primarily balance each other out.

Thus, the region has been oscillating between serving as a carbon source and a weak carbon sink.

A complex picture has emerged

To reach these conclusions about thawing permafrost and its greenhouse gas emissions, the scientists had to use a combination of methods.

“Bottom-up” methods estimated emissions using ground and air-based measurements as well as ecosystem models, whereas “top-down” methods used atmospheric measurements from satellite sensors, including NASA’s Orbiting Carbon Observatory-2 (OCO-2) and JAXA’s (Japan Aerospace Exploration Agency) Greenhouse Gases Observing Satellite.

“This study is one of the first where we are able to integrate different methods and datasets to put together this very comprehensive greenhouse gas budget into one report,” Chatterjee said. “It reveals a very complex picture.”

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