Six to eight times a month, a Sherpa airplane with special instruments takes off from Fairbanks, Alaska, in search of data to answer the question: Is global warming causing changes to the environment that inevitably accelerate the climate change?
That is the suspicion of Charles Miller, principal investigator for a research project that is focusing on greenhouse gas emissions in the skies above the Arctic tundra, the vast treeless region that produces only grasses and low brush during the brief growing season.
"Climate change is already happening in the Arctic, faster than its ecosystems can adapt. Looking at the Arctic is like looking at the canary in the coal mine for the entire Earth system," said Miller, who is based at Pasadena’s Jet Propulsion Laboratory, but who now spends much of the year in Alaska.
The carbon compounds implicated in global warming are often associated with combustion, and that is a significant source. But Miller said the amount of carbon compounds such as methane and carbon dioxide that are trapped in the permafrost beneath the tundra is staggering -- comparable to all of the greenhouse gas emissions from the burning of fossil fuels since the dawn of the Industrial Revolution two centuries ago.
During the summer thaw, the very top of the permafrost melts -- a few inches to no more than a few feet -- releasing only a small amount of the carbon that has built up over eons from the annual die-back of vegetation. It decomposes slowly in the tundra environment and historically is recaptured during the winter freeze.
Enter global warming.
“As temperatures warm, it’s thought that these organic materials could decompose more rapidly and give rise to gases such as carbon dioxide and methane," Miller said. “The anticipated release of carbon should accelerate climate change...I think the experts all agree that that’s the case. The question that we’re grappling with is how much carbon might be vulnerable to release, and how fast might it be released."
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One possible scenario is what scientists call a “positive feedback loop,” akin to what’s known in the more common vernacular as a vicious circle that feeds on itself.
“The warmer it gets the more of this carbon gets released from the thawing permafrost. And it then itself contributes to the warming. So you get this positive buildup -- more and more warming.”
Determining whether that is actually happening is the mission for CARVE -- Carbon in Arctic Reservoirs Vulnerability Experiment, a five-year study now in its third summer.
Ask Miller now if any trends are apparent, and he demurs, wanting to wait for more data. But he does say the airborne surveillance periodically encounter large “plumes of methane,” as much as 150 kilometers (90 miles) across.
There are nuances, as well.
It turns out not all carbon compounds are created equal when it comes to effect on the atmospheric greenhouse. Methane, for example, has a much greater impact than carbon dioxide, as much as 100 times greater over a 20-year period, according to Miller.
What’s more, the climate itself can influence the type of carbon compounds thawing permafrost is more likely to release. Warm and dry is more favorable for carbon dioxide. Warm and wetter would be expected to produce more methane, and it would not take much of a shift to have a significant impact, Miller said.
“Iif the amount of methane to carbon dioxide shifts just a little bit in favor of methane, just one or two percent, then without increasing the amount of carbon that’s released from the soil tremendously you can actually double or even triple the amount of ‘radiative forcing’ and greenhouse gas warming," Miller said. "That’s why we’re really interested in -- whether the arctic is becoming warmer and drier or warmer and wetter.”
With the data CARVE is generating, Miller hopes climate scientists would be able to produce moreaccurate mathematical models for predicting the effects of climate change.