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Ice is melting everywhere—and at an accelerating rate. Rising global temperatures are lengthening melting seasons, thawing frozen ground, and thinning ice caps and glaciers that in some cases have existed for millennia. These changes are raising sea level faster than earlier projected by scientists, and threatening both human and wildlife populations.
Since the industrial revolution, human activity has released ever-increasing amounts of carbon dioxide and other greenhouses gases into the atmosphere, leading to gradual but unmistakable changes in climate throughout the world—especially at the higher latitudes. Average surface temperatures in the Arctic Circle have risen by more than half a degree Celsius (0.9 degrees Fahrenheit) per decade since 1981. The extent of Arctic sea ice cover has decreased by 7–9 percent per decade. And the three smallest extents of summer ice ever seen there have all occurred since 2002. According to the latest forecasts, the Arctic could be ice-free in the summer by the end of this century. (See additional examples.)
The Arctic melt season has lengthened by 10–17 days, shrinking the amount of ice buildup that remains from year to year. As sea ice thins and recedes from coastlines, indigenous hunters and fishers are finding themselves cut off from traditional hunting grounds. Coastal communities face more violent and less predictable weather, rising sea levels, and diminishing access to food sources. Polar bears, unable to cross thin or nonexistent ice to hunt seals, will soon face a severely reduced food source. Scientists fear that with continued melting, the bears may become extinct by the end of the century. Seals, walruses, and seabirds will also lose key feeding and breeding grounds along the ice edge.
Marine transport through the Arctic is expected to increase as ice melts and new shipping routes become available. The length of the navigation season along the Northern Sea Route is projected to increase to about 120 days by 2100, up from the current 20–30 days. While this could have positive economic effects, some observers worry about the environmental costs that might accompany increased ship access to Arctic waters, such as oil spills and fishery depletion.
Arctic permafrost has warmed by up to 2 degrees Celsius in recent decades, with soils thawing to greater depths. By the end of this century, the southern permafrost boundary is projected to shift northward by several hundred kilometers, changing regional vegetation patterns. An estimated 15 percent of the Arctic tundra has already been lost since the 1970s—an area roughly three times the size of California. As permafrost thaws, unstable ground shifts or subsides, damaging buildings, roads, pipelines, and other infrastructure in areas such as Alaska and Siberia.
The Greenland ice sheet is the largest land ice mass in the Northern Hemisphere. It holds enough fresh water to raise the earth’s sea level by 7.2 meters (24 feet) if it were to melt completely, a result expected if the regional temperature rises 3 degrees Celsius. Scientists project that concentrations of greenhouse gases will be high enough by 2100 to push temperatures past this threshold. Satellite data show Greenland’s ice has been melting at higher and higher elevations every year since 1979. A conservative estimate of annual ice loss from Greenland is 50 cubic kilometers (12 cubic miles) per year, enough water to raise the global sea level by 0.13 millimeters a year.
The Amundsen Sea region in the West Antarctic has experienced some of the world’s greatest temperature change, with annual temperatures up 2.5 degrees Celsius over the past 60 years. The glaciers flowing into the sea from the Antarctic continent have been getting thinner for the past 15 years, and ice shelves in the region have decreased by more than 13,500 square kilometers since the 1970s. Since the collapse of the Delaware-sized Larsen B Ice Shelf in 2002, satellites have shown a two- to sixfold increase in the speed of glaciers flowing toward the former ice shelf. While most glaciers typically move a few centimeters to several hundred meters annually, these glaciers are currently moving as much as 1.5 kilometers each year.
This type of acceleration has been witnessed throughout Antarctica and Greenland when ice shelves collapse, removing the barrier to the sea for interior glaciers and quickening the rate of fresh water loss to the ocean. Glaciers in West Antarctica are discharging about 250 cubic kilometers of ice and water into the ocean per year, 60 percent more than is accumulated in their catchment areas—a net change sufficient to raise global sea levels by more than 0.2 millimeters per year .
Ice melting is not limited to the poles. According to glaciologist Lonnie Thompson of Ohio State University, all but 13 of the 2,000 glaciers in southeast Alaska are retreating. Montana’s Glacier National Park may have no glaciers left by 2030, and the ice cap on Tanzania’s Kilimanjaro may disappear completely by 2015.
In South America, Andean glaciers have been melting three times faster in recent years than they were in the mid-twentieth century. Bolivia’s Chacaltaya, once home to the world’s highest ski slope, is estimated to be a mere 2 percent of its former size. It lost two thirds of its mass in the 1990s alone and may disappear completely by 2010. Shrinking glaciers may mean a loss of power in Peru, where 70 percent of electricity comes from hydroelectric turbines powered by the annual runoff from glaciers.
In fact, millions of people living in Asia and South America rely on glacial runoff for drinking water and irrigation. If the glaciers disappear, severe water shortages are sure to follow. Meanwhile, rapidly filling glacial lakes in both the Andes and Himalayas threaten to break their banks and flood towns below.
In Europe, shrinking glaciers and snow cover in the Alps are undermining the continent’s ski and tourism industries. By 2025, Alpine glaciers are likely to contain only half their 1970s volume, dwindling to 5 percent by the end of the century. Pollution from European cities does not help the situation: scientists have measured black carbon concentrations atop these mountains high enough to double the area’s absorption of sunlight.
Such widespread glacial melting has local as well as global effects. Global sea level has risen 10–20 centimeters in the past century. According to the Intergovernmental Panel on Climate Change, up to 1 meter of sea level rise is projected by 2100, with half the rise attributed to melting ice and half to thermal expansion. As sea level rises, inundation and loss of coastal land will force millions of people to relocate.
Warming and melting could force local plant and animal species to adapt or relocate—an increasingly difficult proposition as wildlife habitats are fragmented by expanding human populations. Changes to the food base of ecosystems, such as decreases of algae and plankton in the Arctic Ocean, could have a ripple effect all the way up to the top predators, including the people who hunt and fish these animals.
Most disturbing, many of the effects of ice melting are self-reinforcing. As ice disappears, land and open water are exposed. When sunlight strikes ice and snow, approximately 80 percent is reflected back into space and 20 percent is absorbed as heat. The opposite holds true for land and open water—20 percent is reflected and 80 percent is absorbed. This decrease in reflectivity, or albedo, creates a positive feedback loop, perpetuating the temperature rise and ice melting. Additionally, soot from faraway sources has darkened snow and ice, further decreasing albedo.
Melt water on top of glaciers and ice sheets contributes to fracturing and destabilization of the ice masses and increases flow rates as the water lubricates the underside of the ice. Thawing tundra releases trapped carbon dioxide and methane from newly created wetlands, contributing to further warming. Finally, increased fresh water from melting glaciers and sea ice could alter ocean circulation patterns and destabilize regional climate patterns, perhaps weakening the Gulf Stream and North Atlantic currents that moderate Europe’s climate. Warmer waters may also decrease the ocean’s ability to act as a carbon sink. If no action is taken to halt global warming, these positive feedbacks could quickly send climate change spiraling out of control.
Melting ice is a harbinger of more change to come. Perhaps in the future, children will look back on the fabled polar bears of the icy North Pole the way we imagine woolly mammoths in the last Ice Age. Only this time, we will know who is to blame.
Copyright © 2005 Earth Policy Institute