Greenhouse Effect and Global Warming

Greenhouse Effect

Carbon dioxide and methane are two of a number of so called "greenhouse gases". Greenhouses gases are responsible for the relatively warm temperature of the atmosphere. Without the blanket of greenhouse gases, the Earth would be a frozen ball of ice. The gases of our atmosphere are known as "selective absorbers" of radiant energy. That is, a particular gas absorbs and emits energy well at some wavelengths but not at others. Solar radiation (shortwave) passes through most of the atmospheric gases without being absorbed to a significant extent. However, longwave radiation emitted from the Earth's surface and directed toward the sky is readily absorbed by greenhouse gases. When absorbed, the temperature of the atmosphere increases. Some of this absorbed energy is emitted to space while some is emitted back towards the Earth. This is the basis for the greenhouse effect.

Figure TA.* The Greenhouse Effect

Global Warming

Figure TA.5 Geoscientist examine ice core used to study changes in atmospheric composition. (Courtesy: National Ice Core Laboratory, NOAA)

The fact that atmospheric gases contribute to the heating of the Earth is not new. A hundred years ago, Swedish scientist Svante Arrhenius became the first person to investigate the effect that doubling atmospheric carbon dioxide would have on global climate. Though all atmospheric scientists agree that there is a greenhouse effect, not all agree on the impact that human beings are having on it. In particular, many cannot agree that the present global warming that we are experiencing is a product of human activities. Analysis of ice cores has shown a significant variation in the carbon dioxide content of our atmosphere which has affected global air temperatures since the great ice sheets marched across the continents. Measurements of greenhouse gas concentrations over the last 150 years have shown a steady increase in carbon dioxide with an apparent increase in global temperatures as a result. Research has shown that there has been a 30% increase in the carbon dioxide content since the dawn of the industrial age. This increase is due to a number of activities such as fossil fuel burning, deforestation, and loss of other carbon dioxide "sinks" like wetlands and forests. The burning of fossil fuels releases stored carbon into the atmosphere raising the carbon dioxide content of the air. Forest removal leaves carbon dioxide in the air to enhance the natural greenhouse effect.

departure from long-term normal temp

Figure TA.5 Departure from long-term normal temperature.
Courtesy US EPA

Rising levels of greenhouse gases is thought to cause a rise in global air temperatures. Global mean surface temperatures have increased by .5 - 1.0 F since the latter part of the 19th century. Rising temperatures have caused a decrease in snow cover and sea ice in the Northern Hemisphere. Global sea level has risen by 4-8 inches over the past hundred years. Additional sea level rise and inundation of coastal regions is feared as Antarctic ice sheets and shelves, and smaller alpine glaciers melt. The frequency of extreme precipitation events has increased throughout much of the United States.

Watch "Global Warming 101" Courtesy of National Geographic

Previous | Continue

WebActive: Active Learning on the Web

About TPE | Who's Using TPE | Earth Online

Please contact the author for inquiries, permissions, corrections or other feedback.

For Citation: Ritter, Michael E. The Physical Environment: an Introduction to Physical Geography.
2006. Date visited. http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/title_page.html