By Austin Keating, Nov. 22, 2017 –
Methane, a greenhouse gas frozen by the megatons in Earth’s melting ice, holds the potential to dramatically turn up the thermostat for the planet. But new research shows that a bacterial hero from Earth’s soils and seas will keep the thawing gas at bay.
Methane-eating soil microbes will prevent large plumes of methane from reaching the atmosphere as frozen deposits of it begin to thaw due to climate change, according to a paper in Nature recently published by Vasilii Petrenko and Jeffrey Severinghaus of the Scripps Institution of Oceanography at the University of California, San Diego. While Severinghaus doesn’t study microbes directly, he’s able to show their effect on past climates by going to Antarctica and sampling ancient air, he told colleagues during a presentation at the Comer Abrupt Climate Change Conference in southwestern Wisconsin this fall.
Scientists previously thought thawing methane deposits may have caused an abrupt 50 percent rise in atmospheric methane concentration during a rapid warming period at the end of the Younger Dryas, a cold period that ended 11,600 years ago. The prospect raised alarms for a potentially devastating climate feedback from methane, which molecule for molecule, traps at least 25-times more heat in the atmosphere than carbon dioxide.
Through 10 years of sampling ancient air, Severinghaus, his graduate students and the rest of his team were able to show, however, that during the warming period, no detectable methane in the atmosphere came from thawed deposits.
They demonstrated this by looking at the radiocarbon content of 11,600-year-old Antarctic ice, exhuming a ton for each measurement at a precise and narrow vein of ancient ice originally deposited by snowfall on Younger Dryas glaciers. They gathered a corresponding control of modern-day air cleared of carbon-14 for each measurement as well.
Methane released from thawed deposits has no carbon-14, because it’s old and the radiocarbon content decayed long ago. But methane released from natural sources such as wetlands is fresh, and has detectable carbon-14. Carbon-14 builds up in the air and in all living organic things as cosmic rays bombard atoms in the atmosphere.
“If that 50 percent increase in methane concentration was actually caused by the tundra getting warm and burping out all of this methane, then the concentration of carbon-14 relative to the more abundant carbon-12 should have gone down by 30 percent,” Severinghaus said. “We should really see a huge signal if this idea is correct …and we don’t.”
He added that methane-consuming soil microbes at the time must have stopped most of the thawing methane from reaching the atmosphere—just as their oceanic cousins did when they ate 99.9 percent of the methane released during the Deepwater Horizon oil spill in 2010.
Wetlands, which belch methane when it rains, and other natural sources were the main culprits for the rise in methane during the Younger Dryas warming period, Severinghaus said.
“If it didn’t happen back then, it won’t happen now and it won’t happen in the future,” Severinghaus said. “We can focus our attention back on CO2 [carbon dioxide], which really is the problem, and not worry so much about methane. So check one thing off the list.”
Pennsylvania State Geology Professor Richard Alley concluded Severinghaus’s presentation by applauding the amount of work that went into the research.
“Jeff could stand up here and give five or six more talks that have come out of these samples, it’s just really spectacular,” Alley added.
See related story: Climate Scientists Rebuild the Past To Meet Current Climate Threat
PHOTO AT TOP: Vasilii Petrenko works in the Severinghaus lab, and went to Antarctica to measure radiocarbon in ancient glacial ice. This chamber melts the ice so he can capture and measure the methane content, as the ice traps air bubbles of the atmosphere as it existed 11,600 years ago during a rapid warming event.(Courtesy of Jeffrey Severinghaus)
Note: Austin Keating is a Comer Scholar, a Medill scholarship program supported by the Comer Family Foundation to promote graduate studies in environmental journalism.