Greenhouse Gases

Greenhouse gases include carbon dioxide, methane, and water vapor. These gases are naturally found in small amounts in our atmosphere. However, over the last century, atmospheric concentrations of these gases have been increasing, reaching levels that exceed historic concentrations.

Climate experts see a link between greenhouse gas concentrations and global temperatures because these gases are responsible for keeping Earth warm in the first place. Carbon dioxide, water vapor, methane, nitrous oxide, and a few other compounds readily absorb infrared radiation (heat) coming from Earth's surface, essentially trapping the heat at the Earth's surface. In the proper balance, greenhouse gases make life on Earth possible. However, any increase in the concentration of these gases poses the risk of altering the natural balance and dramatically changing global temperatures.

Graph showing the connection between increased carbon dioxide concentrations in the atmosphere and temperature. Image courtesy of mitopencourseware/Flickr.

Most scientists agree that the recent increase in global temperatures results, at least in part, from human activities rather than solely from changes in Earth's orbit or some other natural cause. Data (including ice core data from the Antarctic and Greenland ice sheets) used to support this conclusion show a rise in concentrations of atmospheric greenhouse gases, such as carbon dioxide (CO2), which correlates roughly with rising global temperatures. You will notice in the graph above that the orange CO2 concentration curve and the green temperature change curve are almost mirror images. Notice that temperatures and carbon dioxide levels increase dramatically close to present-day time. Scientists believe that the increases in carbon dioxide emissions (and subsequently, temperature) were caused by the Industrial Revolution, when fossil fuels began being used in abundance.

The most famous record of changing atmospheric carbon dioxide concentrations is taken from the Mauna Loa Observatory in Hawaii.

Sources and
Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy. This media asset was adapted from Atmospheric Carbon Dioxide Record from Mauna Loa by C.D. Keeling and T.P. Whorf, Carbon Dioxide Information Analysis Center.
Last modified: Tuesday, 7 February 2012, 6:53 PM