This finding, combined with two recent studies, provides not only more evidence that the Earth's ice cover is melting, but that it is melting at an accelerating rate. A study by two Norwegian scientists projects that within 50 years, the Arctic Ocean could be ice-free during the summer. The other, a study by a team of four U.S. scientists, reports that the vast Greenland ice sheet is melting.

The projection that the Arctic Ocean will lose all its summer ice is not surprising, since an earlier study reported that the thickness of the ice sheet has been reduced by 42 percent over the last four decades. The area of the ice sheet has also shrunk by 6 percent. Together this thinning and shrinkage have reduced the Arctic Ocean ice mass by nearly half.

Meanwhile, Greenland is gaining some ice in the higher altitudes, but it is losing much more at lower elevations, particularly along its southern and eastern coasts. The huge island of 2.2 million square kilometers (three times the size of Texas) is experiencing a net loss of some 51 billion cubic meters of water each year, an amount equal to the annual flow of the Nile River.

The Antarctic is also losing ice. In contrast to the North Pole, which is covered by the Arctic Sea, the South Pole is covered by the Antarctic continent, a land mass roughly the size of the United States. Its continent-sized ice sheet, which is on average 2.3 kilometers (1.5 miles) thick, is relatively stable. But the ice shelves, the portions of the ice sheet that extend into the surrounding seas, are fast disappearing.

A team of U.S. and British scientists reported in 1999 that the ice shelves on either side of the Antarctic Peninsula are in full retreat. From roughly mid-century through 1997, these areas lost 7,000 square kilometers as the ice sheet disintegrated. But then within scarcely a year they lost another 3,000 square kilometers. Delaware-sized icebergs that have broken off are threatening ships in the area. The scientists attribute the accelerated ice melting to a regional temperature rise of some 2.5 degrees Celsius (4.5 degrees Fahrenheit) since 1940.

These are not the only examples of melting. My colleague, Lisa Mastny, who has reviewed some 30 studies on this topic, reports that ice is melting almost everywhere--and at an accelerating rate. (See Worldwatch News Brief, March 6, 2000) The snow/ice mass is shrinking in the world's major mountain ranges: the Rocky Mountains, the Andes, the Alps, and the Himalayas. In Glacier National Park in Montana, the number of glaciers has dwindled from 150 in 1850 to fewer than 50 today. The U.S. Geological Survey projects that the remaining glaciers will disappear within 30 years.

Scientists studying the Quelccaya glacier in the Peruvian Andes report that its retreat has accelerated from 3 meters a year between roughly 1970 and 1990 to 30 meters a year since 1990. In Europe's Alps, the shrinkage of the glacial area by 35-40 percent since 1850 is expected to continue. These ancient glaciers could largely disappear over the next half-century.

Shrinkage of ice masses in the Himalayas has accelerated alarmingly. In eastern India, the Dokriani Bamak glacier, which retreated by 16 meters between 1992 and 1997, drew back by a further 20 meters in 1998 alone.

This melting and shrinkage of snow/ice masses should not come as a total surprise. Swedish scientist Svante Arrhenius warned at the beginning of the last century that burning fossil fuels could raise atmospheric levels of carbon dioxide (CO2), creating a greenhouse effect. Atmospheric CO2 levels, estimated at 280 parts per million (ppm) before the Industrial Revolution, have climbed from 317 ppm in 1960 to 368 ppm in 1999--a gain of 16 percent in only four decades.

As CO2 concentrations have risen, so too has Earth's temperature. Between 1975 and 1999, the average temperature increased from 13.94 degrees Celsius to 14.35 degrees, a gain of 0.41 degrees or 0.74 degrees Fahrenheit in 24 years. The warmest 23 years since recordkeeping began in 1866 have all occurred since 1975.

Researchers are discovering that a modest rise in temperature of only 1 or 2 degrees Celsius in mountainous regions can dramatically increase the share of precipitation falling as rain while decreasing the share coming down as snow. The result is more flooding during the rainy season, a shrinking snow/ice mass, and less snowmelt to feed rivers during the dry season.

These "reservoirs in the sky," where nature stores fresh water for use in the summer as the snow melts, are shrinking and some could disappear entirely. This will affect the water supply for cities and for irrigation in areas dependent on snowmelt to feed rivers.

If the massive snow/ice mass in the Himalayas--which is the third largest in the world, after the Greenlandic and Antarctic ice sheets--continues to melt, it will affect the water supply of much of Asia. All of the region's major rivers--the Indus, Ganges, Mekong, Yangtze, and Yellow--originate in the Himalayas. The melting in the Himalayas could alter the hydrology of several Asian countries, including Pakistan, India, Bangladesh, Thailand, Viet Nam, and China. Less snowmelt in the summer dry season to feed rivers could exacerbate the hydrological poverty already affecting so many in the region.

As the ice on land melts and flows to the sea, sea level rises. Over the last century, sea level rose by 20-30 centimeters (8-12 inches). During this century, the existing climate models indicate it could rise by as much as 1 meter. If the Greenland ice sheet, which is up to 3.2 kilometers thick in places, were to melt entirely, sea level would rise by 7 meters (23 feet).

Even a much more modest rise would affect the low-lying river floodplains of Asia, where much of the region's rice is produced. According to a World Bank analysis, a 1-meter rise in sea level would cost low-lying Bangladesh half its riceland. Numerous low-lying island countries would have to be evacuated. The residents of densely populated river valleys of Asia would be forced inland into already crowded interiors. Rising sea level could create climate refugees by the million in countries such as China, India, Bangladesh, Indonesia, Viet Nam, and the Philippines.

Even more disturbing, ice melting itself can accelerate temperature rise. As snow/ice masses shrink, less sunlight is reflected back into space. With more sunlight absorbed by less reflective surfaces, temperature rises even faster and melting accelerates.

We don't have to sit idly by as this scenario unfolds. There may still be time to stabilize atmospheric CO2 levels before continuing carbon emissions cause climate change to spiral out of control. We have more than enough wind, solar, and geothermal energy that can be economically harnessed to power the world economy. If we were to incorporate the cost of climate disruption in the price of fossil fuels in the form of a carbon tax, investment would quickly shift from fossil fuels to these climate-benign energy sources.

The leading automobile companies are all working on fuel cell engines. Daimler Chrysler plans to start marketing such an automobile in 2003. The fuel of choice for these engines is hydrogen. Even leaders within the oil industry recognize that we will eventually shift from a carbon-based energy economy to a hydrogen-based one. The question is whether we can make that shift before Earth's climate system is irrevocably altered.

Lester R. Brown is the founder and president of the Worldwatch Institute.

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