>Global Warning / Arctic Tundra


The Hottest Spot

As the Arctic warms faster than any other place on earth, habitats are either melting or growing like crazy. And that's just the beginning. Researchers fear the impact may open a Pandora's box for climate change, affecting weather and ecosystems the world over.

By Jennifer Bogo

 

In July the Alaskan Arctic looks nothing like the icebox the imagination conjures up. The tundra—frozen and drifted with snow just a month earlier—has thawed by now. It rolls out in a spongy, green-gold carpet, mottled by splotches of shimmering blue lake water, clear to the wall of the jagged Brooks Range. Pink coneflowers and tufts of cottony-white ground willow stud the landscape; knobs of tussock grass bristle out of beds of moss. Cloudberries, crowberries, blueberries, and cranberries lie in flat patches, their blue-black or red fruits clustered among delicate leaves. Stretching through it all, the fat, silver segments of the Trans-Alaska pipeline glint like a giant metal earthworm under the midnight sun.

Fifty-five years ago few outsiders had ever seen Alaska's North Slope, let alone witnessed its change of seasons.

Those who did come, sent by the government, were bent on mapping the territory they knew must hold colossal supplies of oil. During the years they roamed the landscape, they photographed it from the window of a twin-engine plane and inadvertently contributed to the archives of science. Their pictures documented what the place looked like at the time, down to the shape of the shrubs, the face of the rocks, the size of the trees. And then the photos languished for 50-some years, finally left to collect dust in a storage facility.

When snow geophysicist Matthew Sturm first glimpsed one of the photos in 1998, he promptly had all 5,000 of them Fedexed to his office. By comparing those images with aerial photographs taken today, researchers are trying to document long-term changes to Alaska's North Slope, as well as to gain insight into the effect of rapid climate change on Arctic vegetation.

On average, the Arctic has warmed faster than any other region on earth: nearly 5 degrees Fahrenheit over the past 30 years, compared with only 1 degree Fahrenheit over the past 100 years globally. The snow and ice that coat the Arctic landscape reflect up to 80 percent of the solar radiation that beams down. But as greenhouse gases cause temperatures to rise, the snow and ice melt back, and the darker land and water absorb radiation instead. As they warm up, more ice melts, increasing the radiation absorbed, and causing temperatures to rise even further. Climate models predict that during the next century, the Arctic will warm an additional 7 to 12 degrees Fahrenheit.

"One photo pair doesn't tell the story. But when you look at the whole group, you realize the entire landscape is evolving, and it becomes hard to ignore bigger signals such as climate. How else can you explain a change that pervasive?"

By thawing permafrost, lengthening the growing season, and releasing a deluge of nutrients, such a dramatic shift could irreversibly change the habitat of a whole slew of migratory and resident wild-life, as well as the lives of native people. By slowing global ocean and air circulation, the shift could also change the climate, and the ecosystems, of the rest of the planet. Doomsday scenarios that paint the Statue of Liberty in water wings may not be imminent (melting glacier ice raises sea level just millimeters a year), but there is some fact in the fantasy. If the current trend continues, winter will heat up on the Great Plains while more wildfires blaze across California. Northern Europe will experience floods while droughts intensify over southern Africa. So far these predictions are just that, but there is one thing scientists are willing to guarantee: We're in for a big change.

Sturm and his colleagues from the U.S. Army Cold Regions Research and Engineering Laboratory are building their case one photo at a time. They have spent the past three summers flying from the Chukchi Sea east to the Arctic National Wildlife Refuge, a 70,000-square-mile swath of the Alaskan Arctic the size of North Dakota. Following the flight path of the government surveyors has been a challenging ride. As the helicopter banks, only centrifugal force and a seat belt keep Ken Tape securely suspended 500 feet above the tundra. He tightens his grip on his 11-pound camera and, as the exact view in one of the old photos lines up, leans in to get the shot.

Back at the lab, he will compare the two photos and analyze the plant growth in each. "Because there's been no fire disturbance, the North Slope is a really good laboratory for studying changes in vegetation," says Tape, a 26-year-old graduate student in geology at the University of Fairbanks. He holds a black-and-white image from 1948 above a color photo of the same area taken just a year ago. Both show incredible detail. The topography is identical. But the difference in vegetation is striking: In the 53-year lapse, the shrubs all grew bigger, wider, taller, denser. The tree line filled in.

A stable ecosystem, scientists say, would fluctuate over time; plants would spread in some areas, and in others their growth would shrink. But many of Tape's photographs show a dramatic increase in vegetation, such as once bare boulders now camouflaged by leaves, and none show a decrease. By the standards of the Arctic, where growth is measured in mere centimeters, the rate of change in the photos seems explosive. "One photo pair doesn't tell the story," says Tape. "But when you look at the whole group, you realize the entire landscape is evolving, and it becomes hard to ignore bigger signals such as climate. How else can you explain a change that pervasive?"

Ed Rastetter, a senior scientist at the Marine Biology Laboratory in Woods Hole, Massachusetts, is one of many determined to pinpoint the cause. Since 1976 he and other researchers have been covering Alaska's North Slope with a patchwork of experimental plots. They've set up camp in the shadow of the pipeline at Toolik Field Station—a scientific outpost run by the Institute of Arctic Biology at the University of Alaska Fairbanks, and a Long Term Ecological Research site established by the National Science Foundation.

Out behind the MASH-like settlement, Rastetter clomps along wooden planks that zigzag up a hill. He pauses next to a makeshift greenhouse and opens the flap. Compared with the sedge tundra outside, the inside is a veritable jungle, thick with knee-high, tangled dwarf birch straining against the plastic walls.

During the past 13 years the atmospheric temperatures in the greenhouse—one of the newer ones on the site—has been warmed by about 9 degrees Fahrenheit. "Unfortunately, ecosystems take so long to respond to changes in climate that experiments would take hundreds of years to run," says Rastetter. "We don't have that much time." The best the scientists can do is run short-term experiments that simulate future changes—by increasing fertilizer, temperatures, and atmospheric carbon dioxide inside the greenhouses, for instance—and then use computer models to project ecosystem responses a century into the future. Will the Arctic become the scene of Jack's beanstalk, or will the plant growth eventually slow down? In the oldest greenhouses, built 24 years ago, the shrubs are five to six times taller than the vegetation outside.

Rastetter kneels down to demonstrate the reason. He easily pushes a length of pipe into the upper layer of ground and, with a quick twist, pops out a cylinder of moss and soil. It's normal for this top, "active" layer to thaw during the summer, but across the Arctic it's been thawing earlier, and remaining unfrozen for longer, than usual. As this soil warms up, so does the activity of microbes, he explains. Microbes munch on organic matter, releasing nutrients like nitrogen and phosphorus for plants to use. The more nutrients plants have, the more carbon dioxide they absorb from the atmosphere, and, bingo, the shrubbier the vegetation.

According to climate researchers, carbon dioxide is one of the planet's potential killers, a greenhouse gas that traps heat and stimulates changes in climate all over the earth. The more carbon dioxide the plants can absorb, the better. Things are never so simple, however. There is two to three times as much carbon stored in the world's soils as in its vegetation or in the atmosphere, and tundra soils hold more than a tenth of that. Besides releasing nutrients that stimulate plant growth, microbes release soil carbon, too. The world's carbon balance has thus become a race—between microbes releasing carbon dioxide into the atmosphere, and plants flush with nutrients absorbing it back again.

As the Arctic warms, scientists are striving to keep abreast of changes that occur so they can predict the consequences, for Arctic ecosystems as well as for the rest of the world. "Ecosystems from the tropics to the Arctic have the same basic processes," says Rastetter. "They all have microbes that decompose soil organic matter, and they all have plants that absorb carbon dioxide from the atmosphere." A job well done at Toolik means a better understanding of how ecosystems will respond to warming elsewhere.

A warmer Arctic could also have repercussions for the rest of the globe. Initially, it acts as a "heat sink," receiving the surplus energy that builds up at lower latitudes. In order to balance energy across the earth's surface, heat is constantly being transported through atmospheric circulation and ocean currents from the equator to the poles, where it is vented out to space.

But if the climate continues to warm faster in the Arctic than at lower latitudes, the transfer of heat slows down, weakening overall atmospheric circulation. "If you change the nature of the polar heat sink, you change one of the throttles of the climate system," says Mark Serreze, a research scientist at the National Snow and Ice Data Center of the University of Colorado. "The rest of the system has to respond, but just how it will respond we don't really know."

The wild card in predicting the weather for, say, New York City or Lisbon, is the open question of how the ocean will respond. Water is able to hold a tremendous amount of heat and moisture, which, when transferred through its surface to the atmosphere, can further change air temperature and pressure. They, in turn, control the exchange of big air masses.

Some scientists theorize that as low-latitude surface waters warm, it would strengthen El Niño, a natural disruption of the tropical Pacific, and intensify a pattern of winds that sweep over the Northern Hemisphere. These developments could trigger a host of events, like heat waves and flooding, that ripple out across the globe. In polar regions, the presence of sea ice greatly modifies the transfer of heat and moisture between the ocean and the atmosphere. Decreasing sea ice means important changes to ocean-to-atmosphere circulation.

According to satellites, September sea ice—the ice that lasts year-round—has for the past two years been at its record low, shrinking by 14 percent, to roughly 2 million square miles. Over a major portion of the ice-covered Arctic Ocean, sea ice is also 40 percent thinner than it used to be, reveals submarine data—down from more than 9 feet a couple of decades ago to less than 6 feet now. Some climate models predict that by 2070, there may be no summer ice cover in the Arctic at all.

Global ocean circulation is driven by cold, dense water that sinks in the Arctic. This water moves south well below the surface in the Atlantic, pulling warm tropical water north along the surface, where, like a hot-water heater, it releases heat back into the atmosphere. An influx of fresh water to the Arctic Ocean could prevent the water there from sinking and essentially halt this flow. Changes in ocean currents can greatly complicate overall climate change and, among other things, leave North Atlantic countries, like England and eastern Canada, much cooler than they otherwise would be.

It would take but a slight rearrangement in global freshwater influxes to disrupt circulation of the world's oceans. Because a warm atmosphere holds more water vapor, precipitation across the Arctic has already increased more than at any other latitude on the planet, by about 15 percent over the past 40 years. This water flows off the land and into rivers. Records show that the fresh water in Siberia's three largest rivers has swelled by roughly a quarter of the annual flow of the Mississippi River; that water is now being poured directly into the Arctic Ocean.

As rain and snow spill across the tundra, temperatures rise, ice melts, and shrubby vegetation spreads, Arctic wildlife will continue to feel the effects. For instance, woody plants like dwarf birch shade out green plants like ground willow and cotton grass, caribou's preferred food in their summer range, and lichens, their preferred food in winter. The resin in birch leaves, however, is so unpalatable that the animals may actually alter their migration route to avoid birches. "Caribou are very dependent upon the composition of plant communities across their entire range," says David Klein, a professor of wildlife management at the Institute of Arctic Biology. "In fact, their evolutionary food requirements and migratory habits are timed to it."

The same is true for many birds as well. "Almost every Arctic nesting bird will be affected in some way by climate change," says Stan Senner, executive director of Audubon Alaska. "The northward march of woody vegetation may extend the ranges of birds like the Arctic warbler. But birds that nest in open situations, like the long-tailed jaeger, may be limited by more woody vegetation." Earlier snowmelt may allow some birds to nest before they usually do. In 2002 snowmelt at Barrow was 18 days earlier than the long-term average. For the first time, snow buntings raised two separate broods.

Earlier springs also mean that insects, such as parasitic flies and mosquitoes, emerge sooner, and warmer summers allow them to proliferate, passing through their larval stages to more quickly become adults. Large grazers like caribou are particularly vulnerable. They spend less feeding time and more energy just trying to escape these pests. Arctic-nesting Brunnich's guillemots in Canada have also found themselves victims of relentless attack. With upwards of 50 mosquitoes on each leg, they abandon their nests; on the worst days, according to researchers, egg loss is twice as high, too.

Black guillemots initially benefited from an earlier spring as the longer snow-free season enabled them to move north into the Beaufort Sea. But as the climate continued to warm, the floating sea ice that the guillemots depended on to attract fish began to retreat. This summer the ice remained offshore during the entire chick period, says George Divoky, who has been studying the black guillemot colony on Coopers Island since 1975. Just 20 of 140 guillemot pairs were able to find enough food to successfully breed, and even then they had just one chick, while it's typical to raise two.

"Melting of the ice pack occurs as soon as temperatures warm," says Divoky, "and any animal using it will respond just as rapidly." This includes species like ringed seals, which use sea ice to build lairs and rear young, and polar bears, which use the ice as a platform for hunting seals. Because the ice has been melting earlier, polar bears are forced to survive on land and with lower fat reserves. Studies in Canada's Hudson Bay show that every week of early ice breakup costs polar bears 22 pounds. Human hunters have also been affected: The ice has become dangerous and difficult to predict, causing strandings at sea as it breaks away from the shore.

"Because they're out on the land during all different seasons, and have been for centuries, they notice in much more detail the natural world around them," says Graham Ashford, project manager for Inuit Observations on Climate Change, a study funded by the Canadian government. "Like most people, they may not have a clear understanding of greenhouse gases in the atmosphere, but they have a much more sophisticated sense of animals and the weather."

In Sachs Harbour, in Canada's Northwest Territories, Inuit have reported changes in the distribution of wolves, musk oxen, and rabbits. They've also noticed new species such as robins, barn swallows, red foxes, sand flies, salmon, and herring—the names for some of which aren't even in their language. Though winters now feel milder, they say summers are marked by hail, and fall storms are more severe. Winds are stronger, too, causing waves, unhampered by sea ice, to wrack coastal villages. In another Arctic milestone, thunder and lightning now play across the skies.

Inuit have reported changes in the distribution of wolves, musk, oxen, and rabbits. They've also noticed new species such as robins, barn swallows, red foxes, sand flies, salmon, and herring—the names for some of which aren't even in their language.

Extreme conditions are nothing new to inhabitants of the Arctic. During the nine long months of winter, constant darkness and bitter cold are the rule. The terrain is harsh and windswept, the waters choked with ice and the tundra heaped with snow. Yet within this stark environment, animals and people have survived, even flourished, for millennia. They cache their food and don thick layers; they stick together; they sleep. In short, they adapt.

It's the erratic nature of the new Arctic that is so alarming. Photos from 50 years ago show an ecosystem in balance. Five degrees and decades later, old habitats are melting away, and new habitats march north. Coastlines are crumbling, and food moves far from shore. Strong steps to curb climate change may yet provide wildlife and humans with the time needed to adjust, not just in the Arctic, but throughout a changing world.

 



 

© 2003  NASI

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Feeling the Heat
by Jennifer Bogo

Warming in the Arctic will have significant impact on the region's animal and plant life. Here's how some of them could be affected.

1) Musk Oxen
The relatively short legs and small hooves of musk oxen leave them at a disadvantage for moving through deep snow, which is expected to increase during the winter season. Warmer Arctic springs, on the other hand, have caused male grizzlies to wake from hibernation earlier than usual. They move easily across the frozen landscape and have found that whole groups of musk oxen, which band together for defense, make a solid first meal.

2) Walrus
Walrus favor shallow Arctic waters, where they dive for clams and then haul out on sea ice to rest. But though their food supply is fixed, summer sea ice isn't. As the ice retreats north, walrus find themselves many more miles from the food they need to sustain them through winter.

3) Pacific black brant
In the western Arctic, brants raise broods in coastal salt marshes, where they eat sedges down to short, productive "grazing lawns." If warming causes sedges to grow more rapidly, these geese—already a "moderately high" priority on the Audubon WatchList—may not keep up. Tall plants provide less protein per bite, and could produce smaller birds with lower survival rates. Much farther south, warming waters in the Pacific have already caused die-offs of eelgrass, brants' principal winter food.

4) Dunlin
Northern Alaska dunlins, on Audubon Alaska's WatchList as an at-risk species, arrive in the western Arctic just as the tundra emerges from snow cover. They migrate from Asia, where intertidal habitat is being lost to development, and lay their eggs to take advantage of peak insect populations. Warmer temperatures may cause insects to hatch earlier, however, throwing off the carefully timed cycle.

5) Lichen
As shrubs take over the warming Arctic landscape, low-growing lichens will inevitably lose out. Taller plants both block the fall of rain—essential to the otherwise rootless organisms—and shade the lichens from all-important sunshine. That's also bad news for grazers like caribou, which rely on the starch-filled lichens for energy in winter.

6) Spectacled eider
Eiders winter in openings in Bering Sea ice, which, as it retreats, may be affecting the abundance of the clams the ducks prefer to eat. The eiders return to the same shallow, vegetated wetlands to breed year after year. If thawing permafrost in the Arctic tundra allowed these wet areas to drain—or if, conversely, big storms were to flood them—it could pose serious risks to this federally threatened species.

7) Collared lemming
During snowy Arctic winters, the collared lemming is in its prime. Free of predators, it roams the surface in a coat that has turned white, using enlarged claws it has grown to shovel through the hard-packed snow. Longer summers would only improve life for animals competing for the same food, such as tundra voles, brown lemmings, and Arctic ground squirrels.