Photo credit:Lou Albershardt

IPY Traverse Posted: May 6, 2009 Courtesy: Antarctic Sun

by Peter Rejcek The 12 scientists and support staff who made a slow crawl across a vast, blank stretch of East Antarctica this past austral summer for three months to study how regional climate variability relates to global climate change expected to encounter brutally cold storms and other challenges on the high polar plateau. They didn’t expect to come across other travelers in the relatively unexplored area known as Queen Maud Land. But they did — three times in one day. “We were astonished because we were supposed to be all alone,” said Ted Scambos , a member of the Norwegian-U.S. science team that crossed a large slice of the Antarctic continent using tracked vehicles pulling sleds. “I don’t know where you can go in order to be on the edge of the Earth anymore.” The encounters, all involving people taking part in a commercial race to the South Pole, occurred near a fuel depot in an area where the ice sheet was more than 3,000 meters thick, hiding at least four distinct subglacial bodies of water called the Recovery Lakes. “Fuel depots in Antarctica are kind of the equivalent of watering holes in Africa,” mused Scambos, lead scientist at the Boulder, Colo.-based National Snow and Ice Data Center. “Everybody has to come to the fuel depot, and you see all kinds of people, all kinds of groups, gathered at the fuel depot.” But for most of the roundtrip journey between Norway’s Troll research station on the coast and the U.S. Antarctic Program’s South Pole Station , the scientists and crew were on their own. They took measurements of the snow and ice in areas that virtually no one had visited since the late 1960s, when the United States primarily used tractor trains to conduct deep-field science work. Living and working out of bright red, boxed buildings mounted on sleds, the team collected ice cores at various depths and locations, used radar to map the ice sheet layers and dug snow pits — all in an effort to understand the climate in this area for the last thousand years and how it may be changing today. The project was part of the International Polar Year , a 60-nation effort to better understand the Antarctic and Arctic, which officially ended last month. “It’s really been a blank spot on the map — on both the literal map as well as the metaphoric map of climate change in Antarctica,” said Tom Neumann , leader of the traverse team during the second leg of the two-year project that began in 2007-08 and covered nearly 7,000 kilometers including a few side trips. “[The traverse] should help fill in the picture of how Antarctica overall is changing.” Scientists had believed that Antarctica was largely bucking the global warming trend. While West Antarctica was undoubtedly heating up — particularly the outstretched tip of the Antarctic Peninsula where ice shelves are disappearing at historic rates — studies of the much larger East Antarctic Ice Sheet suggested a cooling trend. Some researchers have suggested the depletion of stratospheric ozone over Antarctica — the ozone hole that appears each austral spring — is affecting atmospheric circulation and westerly winds around the continent, effectively shielding it from global warming. But a paper in the journal Nature earlier this year said warming in West Antarctica is greater than whatever cooling may be occurring on the rest of the ice-covered continent. “Simple explanations don’t capture the complexity of climate,” explained Eric Steig , lead author of the Nature paper and a professor at the University of Washington , in a statement back in January. “The thing you hear all the time is that Antarctica is cooling, and that’s not the case,” added Steig, a collaborator on the IPY traverse project. “If anything it’s the reverse, but it’s more complex than that. Antarctica isn’t warming at the same rate everywhere, and while some areas have been cooling for a long time, the evidence shows the continent as a whole is getting warmer.” Antarctica is roughly the size of the United States and Mexico: Snow in Denver doesn’t mean a blizzard stretches all the way down to Mexico City. “Antarctica is a huge place, and I would be surprised if it was all doing the same thing,” said Neumann, a scientist now with NASA Goddard Space Flight Center . Yet there’s even a hint that East Antarctica — well, at least one spot on that incomplete map — may be warming based on one initial experiment by the traverse team. Scambos deployed strings of highly sensitive “thermometers” called thermistors into two of the deeper ice core holes. The temperature on the ice sheet surface changes with the weather, but the temperature deeper down changes very slowly as the climate changes. Neumann likens it to throwing a frozen turkey into the oven — not the best way to cook a turkey, for sure, but eventually the center starts to thaw and cook based on the long-term outside temperature. “It takes a while for the ice at 90 meters to notice how the surface temperature has changed,” Neumann explained. At that depth, the ice temperature is determined by the average temperature of the last 50 years or so. The instruments will operate for the next several years, allowing the scientists to determine how surface temperature changes through time. “The initial results do say these areas are warming,” Neumann said, stressing that the measurements are in the hundredths of a degree per year and the data still raw. Scambos: Recovery Lakes region was likely marine embayment in distant past Most of the scientific analysis is yet to come. Neumann and others on the team will use the ice core samples to conduct stable isotopic measurements. By studying the isotopic ratios of oxygen 16 and oxygen 18, for instance, researchers can figure out what the climate was doing at a particular time because different ratios indicate different types of climate. The chemistry will help the team calibrate the radar returns of the ice layers, a key step to nailing the snow accumulation rates in East Antarctica — one part of the equation to whether the ice sheet is overall losing or gaining mass. Loss of mass would indicate a rise in sea level. “The chemistry from the core helps because it tells you the accumulation rate at a point,” Neumann explained. “For example, how deep is the fallout from the 1960s above-ground nuclear testing? That information helps to calibrate the radar layers that intersect the core site. “If a radar layer is shallower, then it has had relatively less accumulation; a deep layer reflects relatively more accumulation. The information form the core lets you quantify the ‘relative’ statements above.” The scientists also took the opportunity to explore the Recovery Lakes, an area of at least four lakes at the head of one of the largest ice streams draining East Antarctica. Ranging in size from 600 to 1,500 square kilometers, at depths well below sea level, the lakes were likely part of a deep marine embayment millions of years ago when the ice sheet was much smaller, according to Scambos. “It was probably dynamic in the past,” he said. “In the distant future, if the Earth gets a great deal warmer, it would be dynamic again. I would prefer to think that we’ll stabilize climate change before we have to worry about this part of Antarctica disintegrating.” There is still a lot of uncertainty about what the Antarctic ice sheets may do in the future because so little of it has been measured, particularly compared to Greenland, according to Neumann. “The uncertainties in Greenland are getting quite a lot smaller as we get more and more data about ice velocity, ice thickness and accumulation rate. It’s certainly negative [mass balance] and we know roughly how negative it is in Greenland,” he said. “Antarctica is a bit of a different story, because it is so much larger and there’s places with so much less data, such as in East Antarctica. “The physical insight is coming along and the model development is coming along, but I think it’s going to be a quite a while before we really have confidence in the large-scale predictive models of ice sheet change,” he added. More ground-based studies like the traverse would help to continue filling in the blank spots of the climate change map, according to the scientists. “Most of that uncertainty [about Antarctica] can be beaten down with more and more measurements of accumulation rates,” Neumann said. “The traverse system that the Norwegians have put together is fantastic, state-of-the-art. It’s the best in the world right now in terms of supporting a science crew over long distances,” Scambos said. “They essentially have a mobile, 12-person base that provides them relatively easy access to a large area. … [Queen Maud Land is] one of the least-explored areas of Antarctica, and I think that’s going to change, in part, thanks to this traverse system they’ve got.”

Link to this article:
http://antarcticsun.usap.gov/science/contenthandler.cfm?id=1758

Geophysical Research Letters, 36, L10707; doi:10.1029/2009GL037998.

Transient response of the MOC and climate to potential melting of the Greenland Ice Sheet in the 21st century

Aixue Hu, Gerald A. Meehl (Climate and Global Dynamics Division, National Center for Atmospheric Research, Boulder, CO, U.S.A.), Weiqing Han (Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, CO, U.S.A.), and Jianjun Yin (Center for Ocean-Atmospheric Prediction Studies, Florida State University, Tallahassee, FL, U.S.A.)

(Received 3 March 2009; accepted 6 May 2009; published 29 May 2009.)

Abstract

The findings were published this month in the journal Biogeosciences and presented at a news briefing on May 28th.

Single-celled phytoplankton fuel nearly all ocean ecosystems, serving as the most basic food source for marine animals from zooplankton to fish to shellfish. In fact, phytoplankton account for half of all photosynthetic activity on Earth. The health of these marine plants affects commercial fisheries, the amount of carbon dioxide the ocean can absorb, and how the ocean responds to climate change.

Over the past two decades, scientists have employed various satellite sensors to measure the amount and distribution of the green pigment chlorophyll, an indicator of the amount of plant life in the ocean. But with the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite, scientists have now observed "red-light fluorescence" over the open ocean.

"Chlorophyll gives us a picture of how much phytoplankton is present," says Scott Doney, a marine chemist from the Woods Hole Oceanographic Institution and a co-author of the paper. "Fluorescence provides insight into how well they are functioning in the ecosystem."

All plants absorb energy from the sun, typically more than they can consume through photosynthesis. The extra energy is mostly released as heat, but a small fraction is re-emitted as fluorescent light in red wavelengths. MODIS is the first instrument to observe this signal on a global scale.

Above: A global map of red fluorescent light emitted by phytoplankton. Credit: Aqua/MODIS/Mike Behrenfeld, Oregon State University [Larger image]

Red-light fluorescence reveals much about the physiology of marine plants and the efficiency of photosynthesis, as different parts of the plant's energy-harnessing machinery are activated based on the amount of light and nutrients available.

For example, the amount of fluorescence increases when phytoplankton are under stress from a lack of iron, a critical nutrient in seawater. The iron needed for plant growth reaches the sea surface on winds blowing dust from deserts and other arid areas, and from upwelling currents near river plumes and islands. Fluorescence data from MODIS has allowed the research team to study these dynamics.

Right: A map of fluorescent light emitted by plankton in the Indian Ocean, where seasonal monsoons can limit the amount of iron nutrients in the water and stress the plankton to emit more light. Credit: Aqua/MODIS/Mike Behrenfeld, Oregon State University

"On time-scales of weeks to months, we can use these data to track plankton responses to iron inputs from dust storms and the transport of iron-rich water from islands and continents," says Doney. "Over years to decades, we can also detect long-term trends in climate change and other human perturbations to the ocean."

Climate change could mean stronger winds pick up more dust and blow it to sea, or less intense winds leaving waters dust-free. Some regions will become drier and others wetter, changing the regions where dusty soils accumulate and get swept up into the air. Phytoplankton will reflect and react to these global changes.

"NASA satellites are powerful tools," says Behrenfeld. "Huge portions of the ocean remain largely unsampled, so the satellite view is critical to seeing the big picture."

Credits: The research was funded by NASA and involved collaborators from the University of Maine, the University of California-Santa Barbara, the University of Southern Mississippi, NASA’s Goddard Space Flight Center, the Woods Hole Oceanographic Institution, Cornell University, and the University of California-Irvine.

NASA's Future: US Space Exploration Policy

The effect of permafrost thaw on old carbon release and net carbon exchange from tundra

Edward A. G. Schuur*^1,4, Jason G. Vogel^1,4, Kathryn G. Crummer¹, Hanna Lee¹, James O. Sickman² and T. E. Osterkamp³

Arctic thaw could prompt huge release of carbon dioxide

But plant growth initially offsets permafrost carbon release

Anjali Nayar, Nature News, May 27, 2009

More plant growth will absorb some of the carbon dioxide emitted by a warmer Arctic.Punchstock

Thawing Arctic soils could release a billion tonnes of carbon every year by the end of this century, new evidence from test plots in Alaska suggests.

The study by researchers in the United States is one of the first to use radiocarbon dating to calculate the rate of carbon loss from melting tundra soils in situ.

"Previous studies have calculated carbon loss as tundra thaws in the laboratory," says Edward Schuur from the University of Florida in Gainesville, who led the research. "This study is different because we measured the ecosystem response in the real world."

Scientists have long debated how the global climate might be affected by thawing of the Arctic's permanently frozen soils, known as permafrost. When permafrost melts, microbes decompose organic matter in the soil, producing greenhouse gases. But when plants have access to warmer, deeper soils, they grow faster and take in carbon dioxide. Scientists have postulated that CO₂ release by microbes would outweigh any greening of the Arctic by plant life, but the precise balance between the two was not known, says Schuur.

“It's a slow-motion time bomb.”

Edward Schuur

The study by Schuur and his colleagues, published today in Nature¹, shows that after 15 years of thaw, plants initially grow faster and take in more carbon than is released by the melting tundra, so the ecosystem is an overall carbon sink. But after a few decades, the balance shifts and the ecosystem becomes a source of carbon.

"The plants are growing faster, but after a few decades the rate of carbon loss from the soils is so high the plants can't keep up," says Schuur.

It's estimated that permafrost soils store about twice as much carbon than is currently present in the atmosphere², and the stores of carbon are unlikely to run out any time soon. "It's a slow-motion time bomb," says Schuur.

Ecosystem effects

Schuur's team determined how long each chosen test site had been thawing using long-term temperature data and historical aerial photographs. The long-term data enabled the group to determine the ecosystem response to thawing several years into the process, despite conducting the experiment over only three years.

The team calculated the total carbon lost or gained at each test site on the tundra owing to permafrost thaw, using an infrared gas analyser to measure CO₂ concentrations.

The team then used radiocarbon dating to calculate the percentage of total lost or gained carbon that came from the permafrost. Because the isotope carbon-14 is subject to radioactive decay over time, lower levels of carbon-14 suggest it is 'old carbon' that has been locked away from the atmosphere in permafrost for hundreds or even thousands of years.

Extrapolations of the experimental findings to the whole Arctic region suggest that CO₂ emissions from future permafrost thawing could be roughly a billion tonnes per year — of the same order of magnitude as emissions from current deforestation of the tropics. Burning of fossil fuels releases about 8.5 billion tonnes of CO₂ a year.

"This represents an important finding for our predictions of what may happen to tundra ecosystems as the permafrost thawing progresses over the coming decades," says Torben Christensen, a biogeochemist at Lund University in Sweden.

But Christensen points out that future permafrost studies should include measurements of methane gas as well, because of its potential effects on global warming.

“These studies have to be made at other places.”

Martin Heimann
Max Planck Institute of Biogeochemistry

Martin Heimann from the Max Planck Institute of Biogeochemistry in Jena, Germany, adds that although Schuur's study might be accurate in describing his Alaskan test site, there are problems in extrapolating his results across the Arctic. "The Arctic is very heterogeneous," Heimann says. "These studies have to be made at other places."

Heimann also points out that the data from Schuur and his team show interannual variability, which makes it challenging to deduce long-term trends. "The measurements need to be conducted for decades," he says. "But it's a start.

Schuur, E. A. G. et al. Nature 459, 556–559 (2009). | Article |

Schuur, E. A. G. et al. Bioscience 58, 701–714 (2008). | Article |

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Press Release 09-111
Arctic Tundra May Contribute to Warmer World

Researchers predict permafrost thaw will intensify climate change

National Science Foundation, May 27, 2009

A lot of old carbon is stored deep in the tundra where it is locked in permafrost. As these areas start to thaw over about 15 years, large ice wedges in the soil get smaller causing pot-holing and soil depression. The newly available water prompts faster plant growth, and the carbon taken out of the atmosphere by the plants photosynthesizing is greater than the carbon released back into the atmosphere by plants respiring and microbes decomposing carbon. However, after about 50 years, as thawing continues and the soil settles even more, plants are growing faster yet, however the rate of plant respiration and old carbon release through microbes grows even bigger netting more carbon out into the atmosphere than into the soil. Credit: Zina Deretsky, National Science Foundation.

View a video interview with ecologist Ted Schuur (clip1, clip2, clip3) of the University of Florida.

A study published in the May 28, 2009, issue of the journal Nature has helped define the potentially significant contribution of permafrost thaw to atmospheric concentrations of carbon, which have already reached unprecedented levels.

"In earlier work, we estimated that widespread permafrost thaw could potentially release 0.8-1.1 gigatons of carbon per year," said Ted Schuur, an ecologist at the University of Florida and the lead author of the study. "Before this study, we didn't know how fast that carbon could potentially be released from permafrost and how this feedback to climate would change over time."

A large amount of organic carbon in the tundra is stored in the soil and permafrost. This pool of carbon, deposited over thousands of years, remains locked in the perennially frozen ground. In recent years this area began to thaw, providing increased access to plants and microbes that could shift the carbon from the land to the atmosphere.

An understanding of the rate of carbon release is necessary to estimate the strength of positive feedback to climate change, a likely consequence of permafrost thaw. Scientists use the term positive feedback to describe the snowball effect described here: a warmer climate permits permafrost thaw, releasing more carbon into the atmosphere, which will further increase global surface temperature.

From 2004 to 2006, Schuur and his team used radiocarbon dating, a technique typically used to determine the age of artifacts, to track the movement of "old" organic carbon accumulated within the soils and permafrost at an Alaskan site. The ability to distinguish old carbon from newer carbon allowed the researchers to track current metabolism of old carbon in an area where permafrost thaw is increasing.

Surprisingly, this research revealed that during the initial stages of permafrost thaw, plant growth and photosynthesis, which remove carbon from the atmosphere, increase. This increase offsets the release of old carbon from thawing. However, sustained thaw eventually releases more carbon than plants can uptake, overwhelming their compensatory capacities. To put this in a global context, if the average global temperature continues to rise, current calculations predict that positive feedback from permafrost thaw could annually add as much carbon to the atmosphere as another significant source, land use change.

The Alaskan site where Schuur and colleagues carried out their research was monitored over the past two decades, with permafrost temperature measurements beginning before the permafrost began to thaw. This detailed record coupled with Schuur's study of ecosystem carbon exchange and old carbon release provide a comprehensive picture of the dynamics of carbon exchange in response to permafrost thaw.

"Records from this site exist on a decadal time scale, meaning we are able to more accurately account for the slow pace of change within the system. Overall, this research documents the long-term plant and soil changes that occur as permafrost thaws, thus providing a basis for making long term predictions about ecosystem carbon balance with increased confidence," Schuur reported.

Media Contacts
Lisa Van Pay, NSF (703) 292-8796 lvanpay@nsf.gov
Lily Whiteman, NSF (703) 292-8070 lwhitema@nsf.gov

Atmosphere Sea Ice Biology Ocean Greenland Land Warming (red) and mixed (yellow) signals

There continues to be widespread and, in some cases, dramatic evidence of an overall warming of the Arctic system.

	Atmosphere 5° C temperature increases were recorded in autumn			Ocean Observed increase in temperature of surface and deep ocean layers
	Sea Ice Near-record minimum summer sea ice extent			Greenland Records set in both the duration and extent of summer surface melt
	Biology Fisheries and marine mammals impacted by loss of sea ice			Land Permafrost temperatures tend to increase, while snow extent tends to decrease

About the Report Card

Spring agricultural fires have large impact on melting Arctic

Scientists from around the world will convene at the University of New Hampshire June 2-5, 2009, to discuss key findings from the most ambitious effort ever undertaken to measure "short-lived" airborne pollutants in the Arctic and determine how they contribute in the near term to the dramatic changes underway in the vast, climate-sensitive region.

The two-year international field campaign known as POLARCAT was conducted most intensively during two three-week periods last spring and summer and focused on the transport of pollutants into the Arctic from lower latitudes.

One surprise discovery was that large-scale agricultural burning in Russia, Kazakhstan, China, the U.S., Canada, and the Ukraine is having a much greater impact than previously thought.

A particular threat is posed by springtime burning - to remove crop residues for new planting or clear brush for grazing - because the black carbon or soot produced by the fires can lead to accelerated melting of snow and ice.

Soot, which is produced through incomplete combustion of biomass and fossil fuels, may account for as much as 30 percent of Arctic warming to date, according to recent estimates. Soot can warm the surrounding air and, when deposited on ice and snow, absorb solar energy and add to the melting process.

In addition to soot, other short-lived pollutants include ozone and methane. Although global warming is largely the result of excess accumulation of carbon dioxide, the Arctic is highly sensitive to short-lived pollutants. Forest fires, agricultural burning, primitive cookstoves, and diesel fuel are the primary sources of black carbon; oil and gas activities and landfills are major sources of methane.

During the UNH workshop, a report by the Clean Air Task Force detailing some of the campaign's findings on agricultural burning and transport to the Arctic will be officially released.

The report notes that during April, at the beginning portion of the field campaign in Northern Alaska, aircraft-based researchers were surprised to find 50 smoke plumes originating from fires in Eurasia more than 3,000 miles away. Analysis of the plumes, combined with satellite images, revealed the smoke came from agricultural fires in Northern Kazakhstan-Southern Russia and from forest fires in Southern Siberia. The emissions from fires far outweighed those from fossil fuels, the report states.

"These fires weren't part of our standard predictions, they weren't in our models," says Daniel Jacob, a professor of atmospheric chemistry and environmental engineering at Harvard. Jacob participated in a portion of the campaign known as ARCTAS, which used NASA's DC-8 "flying laboratory" to sample plumes of air over Arctic regions in Alaska and Canada.

The international team of scientists used satellites, instrumented aircraft, ocean-going ships, and ground stations to track and analyze pollution transported into the region.

UNH atmospheric chemist Jack Dibb of the Institute for the Study of Earth, Oceans, and Space was also on the DC-8. "We're in agreement that these short-lived pollutants are critical in the Arctic. This meeting is to discuss what we learned from this massive undertaking and what we as a scientific community can recommend to help address the problem," says Dibb.

The work presented at the POLARCAT meeting will benefit the eight-country Arctic Council, which recently voted to jointly undertake efforts to reduce emissions of black carbon, ozone precursors, and methane in order to slow climate change and ice melt in the Arctic. The data will provide more robust results for governments to use in the development of mitigation efforts with the highest likelihood of benefiting Arctic climate.

"Accelerated warming is unraveling the ecosystems of the Arctic region," says Brooks Yeager, executive vice president of Clean Air-Cool Planet.

"Pollutants carried into the region help drive this unprecedented warming and melting, which makes this new science so very valuable, pinpointing as it does the sources and the solutions."

Link to article: http://www.physorg.com/news162565042.html

Burning crops darken Arctic sky, speed polar melt

The collapse of the Soviet Union and the loosening of state control over crop burning in Russia has had an unexpected impact in the Canadian North: the unleashing of massive amounts of soot that is settling on Arctic sea ice and speeding the ongoing polar meltdown.

How the end of the Cold War has fuelled Arctic warming is detailed in a new report by U.S. scientists that points a finger at Saskatchewan farmers for sending some "black carbon" into the Arctic environment but largely blames Russia for the rising number of smoke plumes drifting north and creating a "critical" challenge for Canada and other polar nations.

The findings were released ahead of an international meeting next week at the University of New Hampshire aimed at curbing the impact of agricultural burning — a problem scientists say has emerged as a major factor in Arctic warming and thinning sea ice.

"These fires weren't part of our standard predictions, they weren't in our models," said Daniel Jacob, a Harvard University climate researcher who participated in a multi-agency U.S. government experiment last spring off the northern coast of Alaska.

Teams of scientists led by NASA, the National Oceanic and Atmospheric Administration and the U.S. Department of Energy gathered data on long-range polar pollutants and used NASA's DC-8 "flying laboratory" to sample smoke plumes drifting over Alaska and parts of Arctic Canada.

"What they found surprised them," says the report, Agricultural Fires and Arctic Climate Change, released Wednesday by the Boston-based Clean Air Task Force.

"Over the course of the month, the airplanes encountered up to 50 smoke plumes originating from fires in Eurasia, more than 4,800 kilometres away. Analysis of the plumes, combined with satellite images, revealed the smoke came from agricultural fires in Northern Kazakhstan-Southern Russia and from forest fires in Southern Siberia."

Forest fires have long been identified as a major source of Arctic pollutants, but the study concludes that agricultural fires — typically used to clear stubble from harvested crops and prepare land for the next growing season — are sending more and more smoke northward, warming the Arctic troposphere and then depositing soot on polar snow and sea ice.

The darkened surface reduces the reflective features of the snow and ice and absorbs more heat from the sun, compounding the overall effects of rising temperatures caused by global climate change, the report states.

The study attributes much of the rise in farm-related Arctic pollution to changing land-use practices in post-Soviet Russia and Kazakhstan.

"The collapse of the USSR in 1991 brought an end to the socialist command economy that had dominated agricultural production for decades," the report states. "In the absence of state subsidies, the large farming co-operatives that had supported Soviet industrial society were abandoned, leading to the re-growth of vegetation across much of the countryside. As smaller private enterprises emerged, they faced a changed landscape; cultivated fields now existed alongside wild grasslands and dry brush, creating ideal conditions for fire."

The report says the largely unregulated use of agricultural fires in Russia is now responsible for about 80% of the crop-related black carbon reaching the Arctic.

Canada is contributing just over 1% of the total, the report notes, with most of those agricultural emissions coming from Saskatchewan.

Although farmland burning appears to have declined in recent years in the province, satellite records "nevertheless show extensive fire activity in the crop and grasslands of southern Saskatchewan between January and June 2008," the report says.

The U.S. researchers say the findings about the impact of agricultural fires should prompt stronger action from the Arctic Council, an eight-country organization that includes Russia and Canada and which recently pledged to curb black carbon emissions reaching polar latitudes.

"Targeting these emissions offers a supplemental and parallel strategy to carbon dioxide reductions, with the advantage of a much faster temperature response, and the benefit of health risk reductions," says Ellen Baum, senior scientist of the Clean Air Task Force. "In addition, we have the know-how to control these pollutants today."

Another U.S. study announced on Wednesday also had bad news for the Arctic.

A University of Florida-led research paper to be published in the journal Nature predicted that thawing Arctic permafrost will pump one billion tonnes of carbon dioxide annually into the atmosphere by the end of this century.

Although greater plant growth in the warming Arctic will absorb more CO2 and initially balance the effects of melting permafrost, the research shows the increased vegetation won't fully compensate for carbon unlocked from the soil.

"At first, with the plants offsetting the carbon dioxide, it will appear that everything is fine, but actually this conceals the initial destabilization of permafrost carbon," said study co-author Ted Schurr in a statement released by the university. "But it doesn't last, because there is so much carbon in the permafrost that eventually the plants can't keep up."

A third study — on projected sea-level rises caused by melting Arctic ice — identified coastal cities in the northeast corner of North America, including Halifax, New York and Boston, as the places most likely to face adverse effects.

The study led by the National Center for Atmospheric Research at the University of Colorado incorporated forecasted effects from melting of the Greenland Ice Sheet with earlier predictions about overall increases in ocean levels caused by global warming.

The study, to be published this week in the journal Geophysical Research Letters, found that continued moderate melting of Greenland's ice cap would shift Atlantic Ocean circulation by the end this century and cause sea levels in northeastern Canada and the U.S. to increase between 30 and 51 cm more than in other coastal zones.

"If the Greenland melt continues to accelerate, we could see significant impacts this century on the northeast U.S. coast from the resulting sea level rise," said NCAR scientist Aixue Hu. "Major northeastern cities are directly in the path of the greatest rise."

The researchers also note that "more remote areas in extreme northeastern Canada and Greenland could see even higher sea-level rise" than heavily populated areas to the south.

Those areas include much of Ellesmere Island, Baffin Island, Quebec's Ungava Peninsula and Labrador.

Melting Greenland Ice Sheet may threaten northeast United States, Canada

This visualization (click to enlarge details), based on new computer modeling, shows that sea level rise may be an additional 10 centimeters (4 inches) higher by populated areas in northeastern North America than previously thought. Extreme northeastern North America and Greenland may experience even higher sea level rise. (Credit: Graphic courtesy Geophysical Research Letters, modified by UCAR)

ScienceDaily (May 28, 2009) — Melting of the Greenland ice sheet this century may drive more water than previously thought toward the already threatened coastlines of New York, Boston, Halifax, and other cities in the northeastern United States and Canada, according to new research led by the National Center for Atmospheric Research (NCAR).

"If the Greenland melt continues to accelerate, we could see significant impacts this century on the northeast U.S. coast from the resulting sea level rise," says NCAR scientist Aixue Hu, the lead author. "Major northeastern cities are directly in the path of the greatest rise."

A study in Nature Geoscience in March warned that warmer water temperatures could shift ocean currents in a way that would raise sea levels off the Northeast by about 8 inches (20 cm) more than the average global sea level rise. But it did not include the additional impact of Greenland's ice, which at moderate to high melt rates would further accelerate changes in ocean circulation and drive an additional 4 to 12 inches (about 10-30 cm) of water toward heavily populated areas of northeastern North America on top of average global sea level rise. More remote areas in extreme northeastern Canada and Greenland could see even higher sea level rise.

Scientists have been cautious about estimating average sea level rise this century in part because of complex processes within ice sheets. The 2007 assessment of the Intergovernmental Panel on Climate Change projected that sea levels worldwide could rise by an average of 7-23 inches (18-59 cm) this century, but many researchers believe the rise will be greater because of dynamic factors in ice sheets that appear to have accelerated the melting rate in recent years.

The new research was funded by the U.S. Department of Energy and by NCAR's sponsor, the National Science Foundation. It was conducted by scientists at NCAR, the University of Colorado at Boulder, and Florida State University.

How much meltwater?

To assess the impact of Greenland ice melt on ocean circulation, Hu and his coauthors used the Community Climate System Model, an NCAR-based computer model that simulates global climate. They considered three scenarios: the melt rate continuing to increase by 7% per year, as has been the case in recent years, or the melt rate slowing down to an increase of either 1 or 3% per year.

If Greenland's melt rate slows down to a 3% annual increase, the study team's computer simulations indicate that the runoff from its ice sheet could alter ocean circulation in a way that would direct about a foot of water toward the northeast coast of North America by 2100. This would be on top of the average global sea level rise expected as a result of global warming. Although the study team did not try to estimate that mean global sea level rise, their simulations indicated that melt from Greenland alone under the 3% scenario could raise worldwide sea levels by an average of 21 inches (54 cm).

If the annual increase in the melt rate dropped to 1%, the runoff would not raise northeastern sea levels by more than the 8 inches (20 cm) found in the earlier study in Nature Geoscience. But if the melt rate continued at its present 7% increase per year through 2050 and then leveled off, the study suggests that the northeast coast could see as much as 20 inches (50 cm) of sea level rise above a global average that could be several feet. However, Hu cautioned that other modeling studies have indicated that the 7% scenario is unlikely. [BLOGGER HERE: how many times have we heard this, only to be told later that the model was too conservative?]

In addition to sea level rise, Hu and his co-authors found that if the Greenland melt rate were to defy expectations and continue its 7% increase, this would drain enough fresh water into the North Atlantic to weaken the oceanic circulation that pumps warm water to the Arctic. Ironically, this weakening of the meridional overturning circulation (MOC) would help the Arctic avoid some of the impacts of global warming and lead to at least the temporary recovery of Arctic sea ice by the end of the century.

Why the Northeast?

The northeast coast of North America is especially vulnerable to the effects of Greenland ice melt because of the way the meridional overturning circulation acts like a conveyer belt transporting water through the Atlantic Ocean. The circulation carries warm Atlantic water from the tropics to the north, where it cools and descends to create a dense layer of cold water. As a result, sea level is currently about 28 inches (71 cm) lower in the North Atlantic than the North Pacific, which lacks such a dense layer.

If the melting of the Greenland Ice Sheet were to increase by 3 or 7% yearly, the additional fresh water could partially disrupt the northward conveyor belt. This would reduce the accumulation of deep, dense water. Instead, the deep water would be slightly warmer, expanding and elevating the surface across portions of the North Atlantic.

Unlike water in a bathtub, water in the oceans does not spread out evenly. Sea level can vary by several feet from one region to another, depending on such factors as ocean circulation and the extent to which water at lower depths is compressed.

"The oceans will not rise uniformly as the world warms," says NCAR scientist Gerald Meehl, a co-author of the paper. "Ocean dynamics will push water in certain directions, so some locations will experience sea level rise that is larger than the global average.

Aixue Hu, Gerald Meehl, Weiqing Han, & Jianjun Yin. Transient response of the MOC and climate to potential melting of the Greenland Ice Sheet in the 21st century. Geophysical Research Letters, May 29, 2009. DOI: 10.1029/2009GL037998