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Global
Warming
Global warming is a rise in the average temper-
ature of the earth's climate due to a build-up of
greenhouse gases in the atmosphere. The vast
majority of the world's scientists and a special
scientific panel convened by the U.N. agree
that this trend is underway. Global warming
poses serious dangers, like coastal flooding,
more frequent and intense heat waves, more
extreme droughts, a rise in the number of
severe storms, and the increased spread of infectious diseases.
Some level of greenhouse gases is natural and necessary, as they reduce the rate at which the planet's heat is radiated out into space. But when pollution pushes the level of greenhouse gases in the atmosphere too high, too much heat is trapped, and the world gets hotter.
The most important greenhouse pollutant is carbon dioxide, which is produced from burning coal and oil, and to a lesser extent, natural gas. Deforestation also plays a role as trees that soak up carbon dioxide disappear and those that are burned add additional carbon dioxide to the atmosphere. Global concentrations of carbon dioxide have increased by about 30 percent during the last century, spurred initially by the increase in fossil fuel burning at the onset of the Industrial Revolution. Since it takes decades to centuries for natural processes to remove excess amounts from the air, carbon dioxide, unlike some other pollutants, accumulates in the atmosphere.
In order to stabilize the concentration of carbon dioxide, it will be necessary to reduce emissions to well below their 1990 levels. In the United States the largest sources of carbon dioxide are electric utilities and automobiles.
Other important greenhouse gases include methane, nitrous oxide, and hydrofluorocarbons (HFCs). Methane is produced from landfills, coal mining, oil and gas production and distribution, domestic animals, as well as natural wetlands and rice paddies. The amount of methane in the atmosphere has more than doubled since preindustrial times. Excess nitrous oxide is believed to be due primarily to the use of nitrogen-containing fertilizers in agriculture.
Some hydrofluorocarbons (particularly HFC-134a), which are substitutes for ozone-destroying CFCs, are also strong greenhouse gases. Their contribution to global warming, though relatively small now, could increase in the future.
Consequences of Global Warming
Scientists predict rising temperatures that could have impacts from floods to droughts.
The latest data confirm what a growing number of scientists have been saying for several years -- that the Earth's climate is rapidly changing. According to an assessment prepared by the Smithsonian Institution and several other U.S. agencies, global temperatures increased by about 1 degree Fahrenheit over the course of the last century, and will likely rise even more during this one. Scientists predict that unless greenhouse gas emissions are reduced substantially, temperatures in the United States will rise by about 5 to 10 degrees Fahrenheit on average in the next 100 years, an increase even larger than what's predicted globally.
Such abrupt temperature changes will cause a broad range of impacts. Sea levels will rise, flooding coastal areas. Glaciers and polar ice packs will melt. Heat waves will be more frequent and more intense. Droughts and wildfires will occur more often. And as habitat changes or is destroyed, species will be pushed to extinction. Following are some predicted consequences of global warming, along with recent events and data showing that these changes have, in fact, already begun.
Climate Pattern Changes
Consequences:
Average temperatures will be warmer, with an increase in the frequency of heat waves.
Warning signs:
Most of the United States has already warmed, in some areas by as much as 4 degrees Fahrenheit.
Many places in North America had the hottest seasons or days on record in the late 1990s.
Consequences:
Warmer temperatures could also increase the probability of drought. Greater evaporation, particularly during summer and fall, could exacerbate drought conditions and increase the risk of wildfires.
Warning signs:
April through June of 1998 was the driest period in 104 years in Florida, Texas, and Louisiana.
April through July of 1999 was the driest in 105 years of record-keeping in New Jersey, Delaware, Maryland, and Rhode Island. Dry conditions produced the worst wildfires in 50 years in Florida in 1998.
Consequences:
Warmer temperatures, by increasing the energy of the climatic system, could lead to more intense rainfall at some times and in some areas.
Warning signs:
Precipitation has increased nationally five to 10 percent, mostly due to increases in heavy downpours in some areas.
Vermont, New Hampshire, Rhode Island, and Massachusetts each received more than double their normal monthly rainfall in June 1998.
Glacier and Ice Melt
Consequences:
The rise in global temperatures will increase the melting of glaciers and ice caps, and cause early ice thaw on rivers and lakes.
Warning signs:
At the current rate of retreat, all of the glaciers in Glacier National Park will be gone by 2070.
After 400 years of relative stability, nearly 1,150 square miles of the Larson B and Wilkins ice shelves in Antarctica collapsed between March 1998 and March 1999.
The area covered by sea ice in the Arctic declined by about 6 percent from 1978 to 1995. Ice thickness has decreased 40 percent since the 1960s.
Of 82 years on record, four out of the five earliest thaws on Alaska's Tanana River occurred in the 1990s.
Sea Level Rise
Consequences:
Current rates of sea-level rise are expected to increase as a result of both thermal expansion of the oceans and partial melting of mountain glaciers and the Antarctic and Greenland ice caps. Consequences include loss of coastal wetlands and barrier islands, and greater risk to coastal communities of flooding. Low-lying areas, such as the coastal region along the Gulf of Mexico and estuaries like the Chesapeake Bay, are especially vulnerable.
Warning signs:
Current pace of sea-level rise is three times the historical rate and appears to be accelerating.
Global sea level has already risen by four to eight inches in the past century. Best estimate is that sea level will rise by an additional 19 inches by 2100 with a possible range of five to 37 inches.
Ecosystem Shifts and Species Die-Off
Consequences:
The increase in global temperatures is expected to disrupt ecosystems and result in loss of species diversity, as some species that can't adapt to change or shift their range are lost.
Warning signs:
Some ecosystems, such as alpine meadows in the Rocky Mountains, as well as tropical montane forest and mangrove forest in some locations, are likely to disappear because new warmer local climates or coastal sea level rise will not support them.
In Washington's Olympic Mountains, sub-alpine forest has invaded higher elevation alpine meadows. In Bermuda and other places, mangrove forests are being lost.
In areas of California, shoreline sea life is shifting northward, probably in response to warmer ocean and air temperatures.
Over the past 25 years, some penguin populations have shrunk by 33 percent in parts of Antarctica, due to declines in winter sea-ice habitat.
Health Effects
Consequences:
More frequent and intensive heat waves could result in more heat-related deaths. These conditions could also aggravate local air quality problems, already afflicting more than 80 million Americans. Global warming is expected to increase the potential geographic range and virulence of tropical diseases as well.
Warning signs:
More than 250 people died as a result of an intense heat wave that gripped most of the eastern two-thirds of the United States in 1999.
Disease-carrying mosquitoes are spreading as climate shift allows them to survive in areas that were formerly inhospitable. Mosquitoes that can carry dengue fever viruses were previously limited to elevations of 3,300 feet but recently appeared at 7,200 feet in the Andes Mountains of Colombia. Malaria has been detected in new higher-elevation areas in Indonesia.
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