The greenhouse effect is a natural process by which various gases act like the glass of a greenhouse, trapping heat near the Earth's surface. These gases, commonly called greenhouse gases, are naturally occurring and include carbon dioxide, methane, water vapor, and other trace chemicals.
Human activities are changing and enhancing the greenhouse effect. We are essentially thickening the walls of the greenhouse with a build up of gases. Activities that contribute to a buildup of these gases include the burning of fossil fuels, deforestation, and certain agricultural activities and industrial practices. These activities are unleashing billions of tons of carbon into the environment. Since the Industrial Revolution, atmospheric levels of carbon have increased by more than 30%. We are now experiencing carbon dioxide levels that are unsurpassed in the last 160,000 years.
Global warming is a pollution problem, created by the burning of oil, coal, and to a lesser extent, natural gas. As concentrations of greenhouse gases have continued to rise, global average temperatures have risen by approximately 1 degree Fahrenheit. The average temperatures for the first six years of the 1990s already make this the warmest decade ever recorded in the history of Earth. 1995 was the warmest year on record, and despite severe winter storms around the world, 1996 was the 6th warmest. Unless greenhouse gas emissions are curbed, the Earth's mean temperature is projected to rise by 2 to 6 degrees Fahrenheit in the next century -- a rate faster than any observed during the last 10,000 years.
The United States has been the leading emitter of greenhouse gases for decades. With only 4% of the world's population we account for 22% of global emissions. We emit more carbon dioxide than any other country in the world.
Changes in climate may drastically expand the ranges of many disease carrying insects and rodents. Thereby increasing the incidence of diseases such as malaria, dengue fever, schistosomiasis, and tick-borne diseases, all of which disproportionately affect children. In the next century, global warming may increase the global incidence of malaria by as much as 50 to 80 million additional cases each year, possibly exposing 60% of the world's population to the risk of infection. There is no vaccine for malaria.
Climate-related increases in sea surface temperature and sea levels are expected to increase the incidence of cholera, a deadly diarrheal disease which killed 120,000 people in 1995, mostly children. Increased sea temperatures are also expected to promote algae blooms that can spur the growth of organisms responsible for red tides, increasing the incidence of shellfish poisonings.
Regional stress on agriculture may cause up to 300 million cases of
malnutrition. The availability of fresh drinking water may be threatened
by extremes of the hydrologic cycle (floods and droughts), which are projected
to become more common. Diseases associated with flooding, such as cryptosporidiosis,
as well as diarrheal diseases in developing countries where drought compromises
personal hygiene, could affect millions more people every year.