On a clear, subzero day in Fairbanks, Alaska, I followed researchers Taylor D. Sullivan and Daniel Vandevort to a cold, dusty, underground tunnel.
They fitted hard hats over stocking caps and led me through a corrugated metal tube to the earthen tunnel. Sullivan clicked on his flashlight and panned over walls of terracotta-colored dirt. We were standing inside an airy passageway of permafrost, extending an area of more than five football fields into the side of a hill.
The smell of moldy cheese in a barnyard wafted over us. It smelled of “bison bits and mammoth bits,” said Sullivan, a geophysicist with the Army Corps of Engineers Cold Regions Research and Engineering Laboratory, which owns the tunnel. Vandervort, a civil engineer with the laboratory, said the smell could stick to you for days.
It was March 2022, and I’d come to Alaska to learn about the wildcard of climate change—the vicious feedback loop of Arctic thaw. Many people study permafrost thaw, but few visit the Arctic in the winter. In particular, I was here to see an enduring mystery of permafrost thaw: winter methane emissions.
It’s not just the Arctic: Worldwide, methane emissions have been rising at an accelerating rate since 2007, and scientists aren’t sure why. Last year, about 640 million metric tons of methane entered the atmosphere, and global concentrations hit the highest value recorded since data collection began in 1983.
Although scientists believe that Arctic methane contributes only a tiny fraction of today’s rise in emissions, they worry that will change. Greenhouse gas emissions from thawing permafrost could use up 25%–40% of the allowable emissions to keep climate increase below 2°C, according to Susan Natali at the Woodwell Climate Research Center in Falmouth, Mass.
A seminal discovery by a Russian scientist and an American researcher investigating winter methane emissions in the 1990s revealed a source of methane emissions that was previously unaccounted for. In the years following, estimates of climate warming from permafrost would more than double.
There wasn’t a lot of interaction between Russian and American scientists at the time, a separation that has returned with the conflict in Ukraine. The language barrier kept Russians out of top-tier Western publications, and the country was fresh off the fall of the Soviet Union in 1991.
Terry Chapin, a faculty member at the University of California, Berkeley, at the time, sought to change that for more than merely academic reasons. His wife, Mini, had studied Russian in college. “It was a chance for Mini and me to do science together.”
In 1991, Chapin met Siberian scientist Sergey Zimov at an Arctic climate change conference at Oregon State University. Zimov, a geophysicist, had traveled far. He lived at a remote northern research station in Russia he cofounded in the 1970s with three other families. He’d been studying permafrost, tundra, lakes, and more at the station ever since.
“I was just really impressed with his brilliance,” said Chapin.
Situated far from the halls of Western institutions, Zimov had some far-flung ideas. “We used to have these beautifully long arguments,” said Chapin. “And in almost every case, the things that he was talking about, he eventually convinced me that he was correct.”
One of Zimov’s ideas: Wasn’t it odd that in global databases, atmospheric methane peaked at high latitudes during the winter? “None of this fit with the conventional explanations of what causes methane to be released from the Earth’s surface,” said Chapin.
Over many years, Chapin and his wife visited Zimov in his Northern Siberian Science Station. On the third visit, he worked with Zimov on what would become a fundamental discovery.
Ice Age Buffet
Decades later and hardly a dozen steps on my walk into the permafrost tunnel, a paleolithic bison appeared. Its tusk jutted out near the ground, hidden behind electrical wires. I asked if I could touch it, and Vandervort shrugged. “It’s not a museum.”
The grooves of the tusk felt smooth like a river stone. More bones protruded from the walls, and Sullivan and Vandervort explained their provenance (the last ice age) and age (between about 14,000 and 30,000 years old). These beasts had roamed the grassy plains of Alaska’s interior during the Pleistocene, evading the claws of horse-sized short-faced bears and saber-toothed cats.
Sullivan and Vandervort guided me farther down the corridor hung with string lights, their heels kicking up fine dust. Sullivan stopped to brush his hands through the loose strands of grasslike sedge hanging from the tunnel’s ceiling. The sedge had been dead for 31,000 years, but the cold kept it so perfectly preserved that the blades still shone green with chlorophyll.
Until Chapin and Zimov buddied up, scientists thought these ice age relics had little to do with Arctic thaw. Studies in the early 1990s in Alaska and Minnesota suggested that greenhouse gases from the frozen ground came from modern plants. It’s not so far-fetched: In forests today, trees suck in carbon but eventually decay and release carbon back into the atmosphere. Like a fountain cycling water, the carbon stays in a closed loop.
But during his time in Cherskii, Chapin collected methane samples of lake bubbles above thawing permafrost and brought them back to the United States, where he persuaded a friend to radiocarbon date them. The carbon in the methane was 27,200 years old—it hadn’t wafted through our atmosphere since the time of the mammoth.
Microbes living in the sediments of Siberian lakes were converting ice age carbon into modern-day methane emissions, wrote Zimov and Chapin in their landmark paper in Science in 1997.
Microbes Can Chill
But that wasn’t the only discovery the two made. Zimov dug several cores of permafrost from an eroding Siberian lakeshore. He flooded the cores with lake water and stored them at different temperatures in the lab.
Gas gathered at the top of the cores, and Zimov made a startling finding: Permafrost microbes pumped out methane even at 0°C to 1°C. The microbes living in this wetland ecosystem thrived at cold temperatures.
Zimov’s cores mimicked the environment of many water-bogged permafrost landscapes. In these oxygen-poor environments, ice age debris are no match for bacteria, which digest the cellulose from dead plants into acetate, hydrogen gas, and simple carbohydrates. Hungry methanogens, methane-producing microbes, slurp up these compounds and churn out methane.
Half a world away, I stared at a mirror image of Zimov and Chapin’s Siberian permafrost in the tunnel walls. The permafrost in the Cold Regions Research and Engineering Laboratory just so happened to be “one of the most accessible large-scale exposures of Yedoma permafrost on Earth,” according to a paper in Frontiers in Earth Science. Yedoma, a type of carbon-rich permafrost thick with ice, is the same type that underlies Zimov and Chapin’s lakes, and it’s become synonymous with scientists’ collective anxiety about permafrost thaw.
If thawed, each cubic centimeter of permafrost in front of me could support a billion microbes: A billion microbes jammed into the area of a sugar cube.
“The Chapin paper is prescient in that the winter thaw of lakes is now happening,” said ecologist Ben Poulter, whose work at NASA Goddard Space Flight Center in Greenbelt, Md., tabulates methane sources worldwide.
The pair’s graduate student, Katey Walter Anthony, would go on to prove that methane emissions from lakes could account for half of all warming from permafrost thaw, even though they make up only a tiny fraction of land area.
As it often goes in science, these discoveries started with a simple question about winter methane emissions, and the answer led to more questions than it solved. In the next installment of The Curve, we’ll learn about today’s research into this question involving state-of-the-art airborne sampling, calls to nuclear submarines, and a few angry moose.
—Jenessa Duncombe (@jrdscience), Staff Writer
The Curve is a series charting the mysterious rise of methane in our atmosphere and the quest to find its source.
26 September 2022: An earlier version stated that methane emissions from permafrost thaw could use up 25%–40% of the allowable emissions to keep climate increase below 2°C. This reference has been corrected to include other greenhouse gases released from permafrost thaw.