SUMMARY
Emissions from motor vehicles of toxic and hazardous air pollutants, carbon dioxide, and other greenhouse gases1-emissions that currently are not regulated under the federal Clean Air Act2-are receiving increasing attention at both the federal and state government levels as government officials and members of the public express increasing concern that these substances may pose as much of a threat to public health and welfare as other pollutants from motor vehicles which currently are regulated under the Clean Air Act.Many scientists are reporting a "25-year trend of rising globaltemperatures" and "other dramatic signs of global warming, such as the record shrinkage of the Arctic sea ice cover and unprecedented high ocean temperatures in the Gulf of Mexico."3 Many people attribute global warming to emissions of carbon dioxide and other greenhouse gases resulting fromhuman activities such as the burning of fossil fuels by power plants and motor vehicles.4 Scientists recently have found that the year 2005 was the hottest year on record for the Northern Hemisphere, with temperatures approximately1.3 degrees Fahrenheit above historical average temperatures.5