Energy Future Coalition

Naturally occurring carbon dioxide (CO₂) surrounds the planet like a blanket, keeping in the sun's heat and making life on earth possible.  But by burning fossil fuels (oil, coal, and natural gas) and changing our lands (such as by clearing forests for farmland), we are adding extra CO₂ into the air that traps heat in the atmosphere and alters its natural balance.  Like an extra blanket on a summer night, this additional CO₂ is causing the planet to overheat.  In the past century alone, we have raised levels of heat-trapping pollution in our atmosphere by 36 percent. 

The primary sources of this additional carbon dioxide are power plants—especially coal-fired ones—and other sources that burn gasoline, coal and other fossil fuels. In the U.S., power plants account for 33 percent of all CO₂ emissions. Cars, sport-utility vehicles and other light trucks account for another 17 percent. Every year, one-fifth of humankind's annual emissions of carbon dioxide can be traced to the destructive logging of forests.

Although carbon dioxide produced by burning oil and coal is the primary culprit, a number of other pollutants produced by humans contribute to global warming, as well.  They include methane (agriculture and natural gas consumption), ozone (car exhaust and power plants), nitrous oxide (fertilizer use) and chlorofluorocarbons (refrigerants and aerosol).

We know that the increased CO₂ in the atmosphere comes from fossil fuels because of the "fingerprint" different types of carbon have.  Carbon that has been stored underground for millions of years has a different signature than biologically active carbon.  Scientists are able to measure these differences and therefore pinpoint the causes of CO₂ pollution.