The Human Contribution to Climate Change

Closest to the Earth is a filmy blanket of atmosphere called the troposphere. It contains most of the atmosphere’s water vapor and is where weather takes place. Although most of our air is composed of nitrogen and oxygen, a number of other gases, including those referred to as greenhouse gases, affect air quality. Carbon dioxide, methane, and water vapor are naturally occurring gases in the atmosphere that are referred to as greenhouse gases (GHG) because they let sunlight enter the atmosphere, warm the Earth’s surface and then selectively block some of the heat at infrared wavelengths from being reemitted back into space.*

This natural regulation of Earth’s temperature is referred to as the atmospheric greenhouse effect. Without the greenhouse effect the Earth’s average surface temperature would be 60 degrees F cooler than it is today—and life as we know it would not exist.

For as far back as scientists can gather evidence, the Earth has had many changes in its average temperature, most over a very long time. These were caused by variations in the sun’s intensity, alterations in the earth’s orbit, changes in the position of the continents, and natural catastrophes such as volcanic eruptions and asteroid impacts. Since 1900 the Earth’s average temperature has increased 1.2 to 1.4 degrees F. Nine of the Earth's 10 warmest years on record have occurred since 2001, and all 12 of the warmest years have occurred since 1997, according to the National Climatic Data Center.

The National Climate Data Center collects surface-based temperatures. The Earth System Science Center at the University of Alabama-Huntsville’s data are based on instruments aboard satellites from NASA and the National Oceanic and Atmospheric Administration that measure the atmosphere’s temperature from the surface up to an altitude of about five miles above sea level. The satellite data show that Earth continues to warm unevenly. Warming increases as you go north: the Arctic Ocean has warmed an average of almost 3 degrees in the past 32 years.

Most scientists agree that there is a strong correlation between the increase in temperature and the increased concentration of greenhouse gases in the atmosphere resulting from human activity. These scientists believe the increased concentrations of greenhouse gases enhance the atmospheric greenhouse effect, resulting in increased temperatures.

The human activity that makes the largest contribution to the buildup of greenhouse gases is the burning of fossil fuels to generate electricity and to power automobiles. Another important human factor is clear-cutting forests, which releases the carbon dioxide held in trees back into the air.

The rapid depletion of plant life and the loss of topsoil at desert boundaries and in semiarid regions is another contribution to the buildup of greenhouse gases. This can occur through a combination of drought and the overexploitation of grasses and other vegetation by people.

In response to the U.S. Supreme Court decision in Massachusetts v. EPA (April 2007), the Environmental Protection Agency published its finding Dec. 15, 2009 that greenhouse gases in the atmosphere endanger both the public health and the environment for current and future generations.

* For a more thorough explanation of "The Greenhouse Effect" visit the University Corporation for Atmospheric Research (UCAR)