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  • Saturday, December 9, 2006
    It is not easy to decipher to what extent this human-induced accumulation of greenhouse gases is responsible for the global warming trend. Other factors—natural climatic variations, changes in the sun’s energy, and the cooling effects of pollutant aerosols—affect our planet’s temperature, and understanding in these areas is incomplete.

    Nevertheless, the Intergovernmental Panel on Climate Change (IPCC) stated there is a “discernible” human influence on climate. The observed warming trend is “unlikely to be entirely natural in origin.” In another report, the IPCC wrote, “There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities” (U.S. Environmental Protection Agency).

    While scientists estimate that average global temperatures will continue to increase as levels of greenhouse gases rise, how much and how quickly remains uncertain. The IPCC projects that the planet will warm by an additional 2.2 to 10°F in the next 100 years. This large range is due to various uncertainties, such as future greenhouse gas emission rates, the possible cooling effects of atmospheric particles such as sulfates, and the climate’s response to changes in the atmosphere.

    Even the low end of this warming projection “would probably be greater than any seen in the last 10,000 years, but the actual annual to decadal changes would include considerable natural variability” (ibid.).

    The computer models used to forecast global climate change are still unable to accurately simulate how things may change at smaller scales. As a result, scientists generally feel more certain about large-scale projections (global temperature and precipitation change, average sea level rise) than small-scale ones (local temperature and precipitation changes, altered weather patterns, soil moisture changes).

    As with perhaps all fields of scientific study, uncertainties associated with the science of global warming exist. Some aspects of this science are based on well-known laws and documented trends, while others range from “near certainty” to “big unknowns.”

    Melting Ice
    The Arctic, one of the most forbidding environments in the world, is home to the polar bear. During the summer, these animals roam this region on large chunks of floating ice, drifting for hundreds of miles. This is how they find mates and hunt for seals, fattening themselves to prepare for the severe winter. If these palettes of ice did not exist, the polar bear would not survive.

    Within the past three decades, more than one million square miles of sea ice—an area the size of Norway, Denmark and Sweden combined—has vanished. Presently, ice at the southern Arctic region of the polar bear’s range is melting about three weeks sooner than has previously been the case. This affords the bears less time to hunt, eat and store fat. Due to this early melting, the Hudson Bay polar bear population has declined by 14% during the past ten years.

    Some climate models predict that 50 to 60% of this vital summer sea ice will disappear by the end of this century; others predict that by just 2070, the Arctic will be completely ice-free in the summer. If this does indeed occur, the world’s largest bear could become extinct.

    Meanwhile, glaciers in Greenland are receding at alarming rates. Within the last five years, those along the eastern and western coasts have receded about 300 miles each. Although a total meltdown is highly unlikely, with more than one-fifth of the population living less than two feet above sea level, not much melting is required to cause significant damage.

    Permafrost in the Arctic region is diminishing as well. According to a report in the Geophysical Research Letters, it could shrink by 60 to 90% by 2100. A National Oceanic and Atmospheric Administration climate scientist states that this will increase freshwater runoff into the Arctic Ocean by 28%, lead to the release of large quantities of greenhouse gases from the soil, and upset ecosystems within a wide area
    posted by sasikala at 12:43 PM |