Rapidly rising temperatures already have had an "amazing and potentially troubling" impact in the Arctic, a group of scientists reported in June after a year-long mission to study how global warming is changing the vast ice- and permafrost-covered region that surrounds the North Pole.
The NASA-sponsored mission, called CARVE -- an acronym for "Carbon in Arctic Reservoirs Vulnerability Experiment" -- uses a specially-outfitted plane that flies low and slow above the pristine wilderness of Alaska's North Slope and the Yukon River Valley, allowing it to measure the interaction of greenhouse gases between Earth's surface and the atmosphere.
After its first three flights for 2013 (of a planned seven) concluded in June, the study already had its members re-thinking how quickly the Arctic's permafrost is melting and what that might mean for the carbon stored deep in its frozen soil and sediments.
"Permafrost soils are warming even faster than Arctic air temperatures -- as much as 2.7 to 4.5 degrees Fahrenheit in just the past 30 years," the mission's principal investigator, Charles Miller of NASA's Jet Propulsion Laboratory, said in an interview.
"As heat from Earth's surface penetrates into permafrost, it threatens to mobilize these organic carbon reservoirs and release them into the atmosphere as carbon dioxide and methane, upsetting the Arctic's carbon balance and greatly exacerbating global warming," he added.
What has these scientists alarmed isn't just current levels of carbon dioxide in the atmosphere, which reached an all-time high of 400 ppm in May, breaking through a threshold long considered the benchmark for "a new danger zone."
Melting permafrost potentially poses a much greater danger because it could release massive amounts of methane into the atmosphere. Methane is much more potent as a heat-trapping greenhouse gas than carbon dioxide, with more than 20 times the global warming potential of CO2 over a 100-year period.
Vast reserves of carbon are stored deep within the Arctic permafrost throughout the Northern Hemisphere, an area of frozen soils that covers some 9 million square miles across countries including Canada, Finland, Norway, Russia, Sweden and the United States.
Every summer the top layer of these soils thaws, allowing vegetation to grow that provides food for the animals that live here, like caribou, grizzly bears and the Arctic fox. As these plants and animals die they get caught in the permafrost, which prevents them from decaying.
Year after year, another new layer of plant and animal matter is added to the permafrost, a process that has accumulated stores of carbon that dwarf what has already been released into the atmosphere since the dawn of the Industrial Revolution.
Permafrost zones occupy nearly a quarter of the exposed land area of the Northern Hemisphere. NASA's CARVE mission probes deep into the frozen lands above the Arctic Circle in Alaska to measure emissions of carbon dioxide and methane from thawing permafrost. (Credit: Hugo Ahlenius, UNEP/GRID-Arendal)
As NASA points out in its press release on CARVE: "Over hundreds of millennia, Arctic permafrost soils have accumulated ... an estimated 1,400 to 1,850 petagrams of carbon (a petagram is 2.2 trillion pounds, or 1 billion metric tons). That's about half of all the estimated organic carbon stored in Earth's soils.
"In comparison, about 350 petagrams of carbon [emphasis added] have been emitted from all fossil-fuel combustion and human activities since 1850," the release adds. "Most of this carbon [in the permafrost regions] is located in thaw-vulnerable topsoils within 10 feet of the surface."
The data the CARVE flights collect give scientists more insight into exactly how the gases released from the soils mix and interact with the atmosphere, and how the quickly warming northern latitudes may influence climate change across the rest of the planet.
By flying as low as possible -- about 500 feet -- for eight hours a day over Alaskan tundra, peatlands, wetlands, boreal forest and permafrost, the CARVE mission's C-23 Sherpa aircraft uses sophisticated equipment to "sniff" the air, including a specially-designed spectrometer that analyzes sunlight reflected from Earth's surface to measure carbon dioxide, methane and carbon monoxide.
After each flight, scientists on the ground collect the air samples and ship them off to the University of Colorado's Institute for Arctic and Alpine Research, where they are analyzed to determine whether the carbon they contain came from thawing permafrost.
Determining the source of carbon in the atmosphere above the Arctic is critical because historically, the Arctic's extremely cold and wet soils have stored more carbon than they have released. If a changing climate makes the Arctic warmer and drier, scientists expect most of its stored carbon to be released as carbon dioxide. If it becomes warmer and wetter, however, most of it could be released as methane.
And that, NASA adds, could have a major amplifying effect. "If just one percent of the permafrost carbon released over a short time period is methane, it will have the same greenhouse impact as the 99 percent that is released as carbon dioxide."
At the end of the planned five-year mission, Miller said CARVE hopes to find out whether the Arctic climate has reached an "irreversible tipping point."
"The Arctic is warming dramatically -- two to three times faster than mid-latitude regions -- yet we lack sustained observations and accurate climate models to know with confidence how the balance of carbon among living things will respond to climate change and related phenomena in the 21st century," he said.
"Changes in climate may trigger transformations that are simply not reversible within our lifetimes, potentially causing rapid changes in the Earth system that will require adaptations by people and ecosystems."
MORE: Record Low Sea Ice in the Arctic
Arctic Sea Ice Extent on Aug. 26, 2012
This visualization shows the extent of Arctic sea ice on Aug. 26, 2012, compared to the average sea ice minimum from 1979 through 2010 shown in orange. The sea ice dipped to its smallest extent ever recorded in more than three decades, according to scientists from NASA and the National Snow and Ice Data Center.