THE GREENHOUSE EFFECT

The energy that lights and warms Earth comes from the Sun. Most of the energy that floods onto our planet is short-wave radiation, including visible light. When this energy strikes the surface of Earth, the energy changes from light to heat and warms Earth. Earth’s surface, in turn, releases some of this heat as long-wave infrared radiation.

Much of this long-wave infrared radiation makes it all the way back out to space, but a portion remains trapped in Earth’s atmosphere. Certain gases in the atmosphere, including water vapor, carbon dioxide, and methane, provide the trap. Absorbing and reflecting infrared waves radiated by Earth, these gases conserve heat as the glass in a greenhouse does and are thus known as greenhouse gases. As the concentration of these greenhouse gases in the atmosphere increases, more heat energy remains trapped below. All life on Earth relies on this greenhouse effect—without it, the planet would be colder by about 33 Celsius degrees (59 Fahrenheit degrees), and ice would cover Earth from pole to pole. However, a growing excess of greenhouse gases in Earth’s atmosphere threatens to tip the balance in the other direction—toward continual warming.
Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved.

What Causes Global Warming?

What Causes Global Warming?
From Larry West

Scientists have determined that a number of human activities are contributing to global warming by adding excessive amounts of greenhouse gases to the atmosphere. Greenhouse gases such as carbon dioxide accummulate in the atmosphere and trap heat that normally would exit into outer space.

Greenhouse Gases and Global Warming
While many greenhouse gases occur naturally and are needed to create the greenhouse effect that keeps the Earth warm enough to support life, human use of fossil fuels is the main source of excess greenhouse gases.

By driving cars, using electricity from coal-fired power plants, or heating our homes with oil or natural gas, we release carbon dioxide and other heat-trapping gases into the atmosphere. Deforestation is another significant source of greenhouse gases, because fewer trees means less carbon dioxide conversion to oxygen.

During the 150 years of the industrial age, the atmospheric concentration of carbon dioxide has increased by 31 percent. Over the same period, the level of atmospheric methane has risen by 151 percent, mostly from agricultural activities such as raising cattle and growing rice. The Consequences of Global WarmingAs the concentration of greenhouse gases grows, more heat is trapped in the atmosphere and less escapes back into space. This increase in trapped heat changes the climate and alters weather patterns, which may hasten species extinction, influence the length of seasons, cause coastal flooding, and lead to more frequent and severe storms.

What Is Global Warming?

Global Warming, increase in the average temperature of the atmosphere, oceans, and landmasses of Earth. The planet has warmed (and cooled) many times during the 4.65 billion years of its history. At present Earth appears to be facing a rapid warming, which most scientists believe results, at least in part, from human activities. The chief cause of this warming is thought to be the burning of fossil fuels, such as coal, oil, and natural gas, which releases into the atmosphere carbon dioxide and other substances known as greenhouse gases. As the atmosphere becomes richer in these gases, it becomes a better insulator, retaining more of the heat provided to the planet by the Sun.

The average surface temperature of Earth is about 15°C (59°F). Over the last century, this average has risen by about 0.6 Celsius degree (1 Fahrenheit degree). Scientists predict further warming of 1.4 to 5.8 Celsius degrees (2.5 to 10.4 Fahrenheit degrees) by the year 2100. This temperature rise is expected to melt polar ice caps and glaciers as well as warm the oceans, all of which will expand ocean volume and raise sea level by an estimated 9 to 100 cm (4 to 40 in), flooding some coastal regions and even entire islands. Some regions in warmer climates will receive more rainfall than before, but soils will dry out faster between storms. This soil desiccation may damage food crops, disrupting food supplies in some parts of the world. Plant and animal species will shift their ranges toward the poles or to higher elevations seeking cooler temperatures, and species that cannot do so may become extinct. The potential consequences of global warming are so great that many of the world's leading scientists have called for international cooperation and immediate action to counteract the problem.

Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved.