After a thorough examination of the scientific evidence and careful consideration of public comments, the U.S. Environmental Protection Agency (EPA) said that greenhouse gases (GHGs) threaten the public health and welfare of the American people. For the first time, the EPA pointed to GHG emissions from on-road vehicles as a major source in addition to coal-fired power plants.

GHGs are the primary driver of climate change, according to the EPA, which can lead to hotter, longer heat waves that threaten the health of the sick, poor or elderly; increases in ground-level ozone pollution linked to asthma and other respiratory illnesses; as well as other threats to the health and welfare of Americans.

“These long-overdue findings cement 2009’s place in history as the year when the U.S. Government began addressing the challenge of greenhouse-gas pollution and seizing the opportunity of clean-energy reform,” said EPA Administrator Lisa P. Jackson. “Business leaders, security experts, government officials, concerned citizens and the U.S. Supreme Court have called for enduring, pragmatic solutions to reduce the greenhouse gas pollution that is causing climate change. This continues our work toward clean energy reform that will cut GHGs and reduce the dependence on foreign oil that threatens our national security and our economy.”

The EPA’s final findings respond to the 2007 U.S. Supreme Court decision that GHGs fit within the Clean Air Act definition of air pollutants. The findings do not in and of themselves impose any emission reduction requirements but rather allow the EPA to finalize the GHG standards proposed earlier this year for new light-duty vehicles as part of the joint rulemaking with the Department of Transportation.

On-road vehicles contribute more than 23% of total U.S. GHG emissions, according to the agency. The EPA’s proposed GHG standards for light-duty vehicles, a subset of on-road vehicles, would reduce GHG emissions by nearly 950 million metric tons and conserve 1.8 billion barrels of oil over the lifetime of model year 2012-2016 vehicles.

The EPA’s endangerment finding covers emissions of six key greenhouse gases—carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride—that have been the subject of scrutiny and intense analysis for decades by scientists in the United States and around the world.