Carbon dioxide is a greenhouse gas that is linked to global warming and climate change.

Carbon footprints represent our contribution to global warming by measuring the annual amount of CO2 we emit into the atmosphere.

Although common examples of carbon emissions include burning fossil fuels for heating and gasoline for driving, many other lifestyle choices affect carbon footprints.

Conserving energy, reducing meat consumption and recycling can reduce carbon footprints. Shopping habits also play a role, since product labels sometimes designate manufacturers or products for their energy-saving habits and properties.

Ecological footprints are a similar measure of lifestyle habits. These footprints address land and water conservation.

In data collected between 1990 and 2003 by the U.S. Department of Energy's Carbon Dioxide Information Analysis Center, the United States was ranked 11 out of 211 countries for CO2 emissions per capita.

Despite the nation's collective ranking, many individuals are calculating their personal carbon footprint and seeking ways to reduce it.

A variety of Internet programs have been designed to calculate your carbon footprint. Examples can be found at www.carbonfootprint.com, www.web.conservation.org/xp/CIWEB/programs/climatechange/carboncalculator.xml and www.seegreennow.com/.

To calculate your ecological footprint, go to www.myfootprint.org/.