The US federal government has ruled that CO2 is a pollutant

The EPA recently ruled that carbon dioxide is a pollutant.[[Environmental Protection Agency. “Proposed Endangerment and Cause or Contribute Findings for Greenhouse Gases Under Section 202(a) of the Clean Air Act; Proposed Rule.” (PDF) Federal Register 74, no. 78 (April 24, 2009): 18886-18910. pdf.]]

The reasoning behind the ruling is that, while CO2 is generated naturally by plants and by geologic processes, CO2 levels are rising in the atmosphere, and the increase comes mostly from burning fossil fuels. Because carbon dioxide levels help set the planet’s temperature, experts estimate that that average global temperature could rise 7F over pre-industrial levels by the end of the century, leading to significant rise in sea level, increased droughts, more floods, more severe weather events, disruptions of agriculture and more.

Depending upon how EPA enforces its ruling — or if Congress enacts new legislation — the owners of coal-fired power plants, which emit a great deal of CO2, may have to resort to a variety of new technologies to reduce emissions — and indeed, they are already exploring such technologies, collectively known as “clean coal.” Without changing the way energy is produced, significant reductions in emissions through other means, such as efficiency, will not be adequate to avoid significant climate disruptions