The Arctic’s thawing ground is releasing a shocking amount of dangerous gases
Nature News

The Arctic’s thawing ground is releasing a shocking amount of dangerous gases

In the black spruce forests along the Tanana River in central Alaska, scientists Miriam Jones and Merritt Turetsky watched for years as trees tipped, leaned, and toppled into boggy ground. Over time, the earth below weakened and grew soupy. This once-hard soil, thick with ice, was heating up, sinking and filling with rain and snow melt.

Scientists have known for decades that as rising temperatures thaw the northern latitudes, previously frozen soil called permafrost will release greenhouse gases, which in turn will speed up global climate change.

But based in part on what they learned by studying Alaska’s “drunken forests,” Turetsky, Jones and a team of experts this week confirmed something else: Warming of small patches of frozen ground that contain large veins of ice will release far more emissions than once thought.

This process, called “abrupt thaw,” will probably hit just 5 percent of Arctic permafrost. But that will likely be enough, conservatively, to double permafrost’s overall contribution to the warming of the planet, the team of researchers led by Turetsky concluded in a study published Monday in the journal Nature Geoscience.

“It’s a little change, but it can have a big punch,” says Turetsky, director of the Institute for Arctic and Alpine Research at the University of Colorado.

Abrupt thaw is not a cause for alarm, the scientists say. Permafrost will still produce fewer emissions than our own burning of coal, oil and natural gas. David Lawrence, a senior scientist at the National Center for Atmospheric Research in Boulder, Colorado, said that—until now— thawing permafrost had been expected to amplify human-caused climate change by about 10 percent.

But doubling that figure is significant because the Intergovernmental Panel on Climate Change—the global organization that estimates how quickly we need to stop burning fossil fuels to keep the worst warming at bay—has not taken permafrost fully into account.

In other words, if we hope to hold warming to 2.7 to 3.6 degrees Fahrenheit (1.5 or 2 degrees Celsius), we’ll have to make the shift to renewable energy faster than we think.

Carbon freezer breaking down

While Turetsky’s results weren’t published until this week, her years of research, and that of several of her co-authors, formed the basis for a story in the September 2019 issue of National Geographic magazine.

The story showed that scientists have known for a long time that permafrost holds nearly twice as much carbon as the atmosphere—mostly the partially decayed remains of ancient plants and animals. No one expects all or even most of that ground to thaw, and most of what does will thaw gradually over decades, slowly releasing mostly carbon dioxide. Some portion of that CO2 will even be taken up by plants as warming temperatures spark increased greening of Arctic vegetation.

But a small fraction of the Arctic’s nine million square miles of permafrost is packed with solid ice. When that ground thaws, the ice melts, dramatically altering the landscape. The ground slumps to fill the void left behind by once-frozen water, creating divots in the earth that turn into ponds, even lakes. All that moisture speeds up thawing even more.

Warming ground also exposes carbon-rich peatlands that have been locked in this freezer for thousands of years. It can spark landslides, churn up old soils. And across many parts of the Arctic these changes are happening faster than once expected. On one northern Canadian island, ground slumps already have increased 60-fold from 1984 to 2013.

Here’s why all of this matters: Once that solid ice begins to drain, many landscape shifts can take place virtually overnight, in just days, weeks, or months. And when the changes happen, far more of the carbon held in those ice-thick lands gets released as methane, which can be at least 25 times more potent a greenhouse gas than CO2.

Sometimes scientists can even see it. Katey Walter Anthony, with the University of Alaska, Fairbanks, often goes out in the dark of an Arctic winter and pokes holes in iced-over ponds. By holding out a flame she can document whether methane is escaping.

Each spring for years, Jones and Turetsky, both Arctic wetland experts, took snowmobiles into interior Alaska to sample permafrost. Once, a few years ago, Jones, with the U.S. Geological Survey, looked into a hole in the ground she’d just created with her instruments. Down several feet she saw bubbling. The ground had become so warm that microbes were feeding on the ancient plant matter, releasing methane through the moist soil. “It looked like it was boiling,” Jones says.

Permafrost counts

The study Turetsky published this week is the first that attempts to quantify all of the ways these permafrost changes can contribute to greenhouse gas emissions—and just how large that contribution is.

“Most of us going in thought it would be much smaller,” co-author Lawrence says. “It was surprising.”

The takeaway, Lawrence says, is that permafrost will make it even harder to meet our emissions targets.

Computer models that project how emissions affect global temperature changes are only just beginning to simulate permafrost thaw. The last major IPCC assessment in 2014 didn’t incorporate permafrost emissions at all. In 2018, the IPCC’s special report on how to cap temperature rise at 2.7 degrees F said global fossil fuel emissions needed to be cut 45 percent by 2030 and completely by 2050. That report used a simplified model to estimate gradual thaw—and didn’t incorporate abrupt thaw at all.

Scientists know that must change. “We need to be setting our policy targets now” to begin hastening the transitioning to cleaner energy, Turetsky says. If governments don’t account for permafrost feedbacks, “how realistic are our projections?”

But it’s also not entirely clear how researchers will resolve this. Arctic landscapes are vast and poorly monitored, and other factors—such as increases in Arctic wildfires—can prompt even more speedy thawing.

Charles Koven, a staff scientist with the Lawrence Berkeley National Lab, is a lead author on the next IPCC assessment, tackling a chapter on the carbon cycle. He’s also a co-author on Turetsky’s paper.

“We are aware of and will be taking into consideration these results,” Koven says.

In one strange way, Turetsky argues, the odd landscape behavior researchers are documenting as ice-rich permafrost thaws could be considered a gift.

“Changes in the Arctic sound scary,” she says. But “the Arctic is revealing its lessons while we are still in control of our future. The Arctic is telling us what’s going to happen around the world in coming decades.”

We just need to listen—and ramp up our response accordingly.

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