Don’t be fooled by seemingly “permanent” permafrost
Climate Watch is an analysis of the latest news about the science, politics, and policy of global climate change. Views expressed in this article are those of the author and not necessarily those of the American Chemical Society.
10.1021/es802699z
great risk of thawing because of global warming. And this layer is the most worrisome component, because it contains the most carbon. Other new research has also found that even more carbon is stored in permafrost than had been COURTESY OF DUANE FROESE
When geologist Duane Froese of the University of Alberta (Canada) found a 740,000-year-old wedge of ice poking out of Yukon’s frozen soil, he knew that his discovery might be spun out of context. Scientists have become increasingly concerned about permafrost because as it thaws, it releases CO2, methane, and other greenhouse gases that could kick global warming into higher gear. But Froese’s discovery of ancient permafrost suggests that some permafrost has survived climates warmer than today’s. “I worry about the climate skeptics thinking we don’t have to worry [about permafrost thawing],” he says. He even wrote his own press release so that he could tailor the message. He was right to worry, at least in part. News reports soon followed with headlines like “Ice chunk suggests permafrost quite hardy” by the Canadian Press and “Permafrost may not thaw even during global warming” in the New York Times. According to the latter story, Froese’s study, published September 19 in Science (2008, 321, 1648), “suggests that the impact of warming on the permafrost may not be as bad as forecast.” The old Canadian ice has apparently survived several warm periods, including the last interglacial period (the period between ice ages) 120,000 years ago. Before letting out a sigh of relief, though, read to the bottom of these articles to get the whole picture. Froese points out that the top few meters of permafrost are still at
This relict ice wedge was formed during the Pleistocene epoch, when temperatures were colder than today; it survived underground for hundreds of thousands of years in the Arctic.
thought previously, much of it deeper than the top foot or so that researchers had been focusing on. The new findings, taken together, bring to light a basic question: how much carbon is really vulnerable to global warming caused by human activities in coming decades?
There’s old, and then there’s old The wedge that Froese’s team found was in the Klondike region in the central Yukon, and it’s the oldest ice ever found in North America. Ice wedges form when the soil cracks in very cold winters and then fills with spring meltwater that freezes. This one was exposed by gold mining activity; Froese first saw it in 2000 but
2008 American Chemical Society
Published on Web 10/08/2008
wasn’t able to estimate its age until 2005, when rains uncovered a layer of volcanic ash, or tephra, that could be used for dating. The ice is in a relatively warm area of discontinuous, or patchy, permafrost. “If you were looking for old permafrost, this isn’t where you would start,” Froese says. He established the ice’s age using fission track dating, which adds up tracks made in volcanic glass by the radioactive decay of uranium, and he confirmed it using paleomagnetism and fossils at the site. “It’s a cool thing to find this piece of ice 700,000 years old in a place where we wouldn’t have expected it,” says ecosystem ecologist Ted Schuur of the University of Florida, who is studying Alaskan permafrost. “But is this a widespread pattern or is this a very local phenomenon?” he asks. Froese says it’s hard to say how much ice could be this old globally, but it’s not likely to be very common. “I think it will take more geological evidence to prove that these ice wedges are so old,” says Vladimir Romanovsky of the University of Alaska Fairbanks. He notes that there are examples of ice surviving other warm periods, such as the Holocene Optimum about 9000 years ago, when temperatures were 1-2 °C warmer than today, as well as the last interglacial period 120,000 years ago. “But you have to remember that this is only in particular places,” he adds. “In Siberia, there is a lot of evidence that permafrost was degrading very deeply not only during the last interglacial but [also] in the Holocene Optimumsit thawed down to 200 meters deep.” The general rule, he adds, is that most of the top few meters of permafrost thawed during those warm spells.
December 1, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 8623
8624 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / December 1, 2008
therefore more protected from warming, than the permafrost Ping described. Confirming Ping’s finding is an analysis of worldwide data sets published in the September issue of Bioscience (2008, 58, 701-714). In that paper, Schuur and colleagues estimate that 1672 Pg of carbon is stored in permafrost (of that, 1024 Pg in permafrost up to 3 m deep), which is more than double the previous estimate and twice the current atmospheric carbon pool. The amount of carbon that could be released from permafrost as CO2 or methane depends largely upon how much warming occurs. Estimates for this century range up to 1 Pg of carbon per year, similar to emissions from land-use changes such as deforestation. That would add roughly 25-50 parts per million of CO2 to the atmosphere over the next century, says Howard Epstein, an ecologist at the University of Virginia and these coauthor with Ping of the Nature Geoscience paper. Permafrost could disappear even more quickly, depending on physical dynamics. “The process can go faster when there is a lot of ice in permafrostswhen it melts, we can expect to see this layer just falling apart,” Romanovsky notes. This happens, for example, when soil collapses as so-called thermokarst, which is already causing trees to fall over in some parts of the Arctic. “If just 10% of the [global] permafrost pool thaws, that’s almost 200 gigatons [of carbon]. If that comes out this century, that’s a huge amount, but it still allows for a huge stable pool,” Schuur says. —ERIKA ENGELHAUPT NATIONAL PARK SERVICE/LARISSA YOCUM
banks and colleagues estimate that Froese emphasizes that he and Arctic soils in Alaska contain an his colleagues still think that peraverage of 34.8 kilograms of soil mafrost, especially near the surface, organic carbon per square meter, is vulnerable to climate change. 60% more than previously pub“This paper is really concerning the lished estimates. The researchers deep part of permafrost, that more extrapolate from that figure the than a few meters below the suramount of organic carbon in all face,” he adds. Arctic soils in North America, and The news coverage of Froese’s get 98.2 petagrams (Pg), or billion study illustrates an ongoing probmetric tonssequivalent to approxilem with climate change coverage mately one-sixth of the current carin general: the consensus on many bon content of the atmosphere. issues tends to get lost among re“Previous estimates of the Arctic ports highlighting controversies at carbon stores were based on very the cutting edge, such as new findlimited sampling and only [of] the ings that appear to go against the prevailing wisdom. Scientists who study permafrost have reached a strong consensus on this much: permafrost is storing a lot of carbon that could be released in a warmer world. “Even previous estimates said there’s as much carbon in permafrost as in the atmosphere now, so that [atmospheric carbon] would double if all the permafrost thaws,” says Oliver Frauenfeld of the National Snow and Ice Data Center in Colorado. “And permafrost is not incorporated Permafrost is already thawing in the Arctic, causing at all in any global climate models right now [as contribut- so-called drunken trees to shift and lean. ing to future warming],” he adds. surface-stored organic carbon,” Ping says. Most work has focused Depth matters on the top 10 centimeters (cm) of Other new studies reveal that scisoil, which can be easily sampled entific understanding of permafrost with shovels. Ping’s team used is indeed incomplete, but the gaps jackhammers to chisel soil 1 meter in knowledge point toward a (m) deep at 117 sites and found greater, not smaller, permafrost large stores of carbon 50-120 cm role in accelerating global warming. deep in most upland tundra soils. By looking deeper in permafrost, “This ‘deep’ carbon accounts for scientists have found an even more nearly 50% of the total carbon store vast pool of stored carbon than of that terrestrial ecosystem,” Ping they had imagined. notes. Two recent papers estimate that Froese is not sure exactly how there could be twice as much cardeep the 740,000-year-old ice was, bon stored in permafrost as previbecause it was brought to the surously thought. In their study in face by mining activity; he estiNature Geoscience, Chien-Lu Ping mates that it was 3-4 m deep. That of the University of Alaska Fairestimate would place it deeper, and
