GLOBAL WARMING - HARMFUL FOR POLAR BEARS AND FOOD CHAIN AND OZONE LAYER DEPLETATION

OZONE LAYER DEPLETATION

 The ozone layer is a region in Earth's stratosphere that contains high concentrations of a bluish gas called ozone. Although ozone constitutes only about one millionth of the atmosphere's gas es, it absorbs most of the sun's ultra violet radiation. Without the ozone layer, this radiation would destroy all life on the surface of the planet. Ultraviolet radiation creates and perpetuates ozone. When an ozone molecule is struck by an ultraviolet ray, it falls apart, yielding free oxygen and an oxygen atom that combines with an other free oxygen to form more ozone. This cycle absorbs most UV radiation. Some manufactured chemicals interfere with this cycle, thus reducing the amount of ozone in the stratosphere. Among the worst offenders are chlorofluorocarbons (CFCs), usually found in refrigerants and aerosol sprays and now generally banned. Falling ozone levels have caused a thinning of the ozone layer above Antarctica, known as the ozone hole. The Antarctic ozone hole increased dramatically in size in the 1980 s and 90 s, but has  stabilized in recent years. A smaller hole over the Arctic is now developing.

GREEN HOUSE EFFECT

The greenhouse effect allows the short-wave radiation of sunlight to pass through the atmosphere to Earth's surface but makes it difficult for heat in the form of long-wave radiation to escape. This effect blankets the Earth and keeps our planet at a reasonable temperature to support life. Earth radiates energy, of which about 90 percent is absorbed by atmospheric gases: water vapour, carbon-dioxide, ozone, methane, nitrousoxide, and others. Absorbed energy is radiated back to the surface and warms Earth's lower atmosphere. The gases have come to be called greenhouse gases because they hold in light and heat, just as a greenhouse does for the sake of the plants inside. Greenhouse gases are essential to life, but only at an appropriate balance point. These gases increased during the 20th century due to industrial activity and fossil fuel emissions. For example, the concentration of carbon dioxide in the atmosphere has recently been growing by about 1.4 percent annually. This increase in greenhouse gases is one of the contributors to the observed patterns of global warming.

IMPACT OF GLOBAL WARMING ON POLAR BEARS

In May 2008, the United States added the polar bear to the list of threatened species protected under the U.S. Endangered Species Act. Activists had supported the listing for a number of years, recognizing that the polar ice cap was melting at even a greater rate than predicted—with new estimates that it might melt completely by 2099.

Polar bears rely on the ice cap to stage their hunting of ringed seals and other prey, so the loss of the ice poses a distinct threat to their survival.

While a robust male polar bear can measure II feet tall and weigh up to 1,200 pounds, there is evidence that the species is losing its vigor and suffering a decline in size. There has also been a noticeable decline in the survival rate of cubs, which usually are born as twins in the winter.