The U.S. Environmental Protection Agency (EPA) confirmed Monday what most of us have suspected for quite some time: “science overwhelmingly shows greenhouse gas concentrations at unprecedented levels due to human activity.”

The report, delivered by EPA Administrator Lisa P. Jackson, proves that greenhouse gases (GHGs) threaten Americans’ health and welfare, and emissions from on-road vehicles contribute to this threat.

Greenhouse gases are the primary driver of climate change, which can lead to hotter, longer heat waves that:

• Threaten the health of the sick, poor and elderly
• Increase ground-level ozone pollution that’s linked to asthma and other respiratory illnesses
• Pose other threats to Americans’ health and welfare

“These long-overdue findings cement 2009’s place in history as the year when the United States government began addressing the challenge of greenhouse-gas pollution and seizing the opportunity of clean-energy reform,” Jackson says. “Business leaders, security experts, government officials, concerned citizens and the United States 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.”

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 they allow the EPA to finalize the GHG standards proposed earlier this year for new light-duty vehicles, as part of a joint rulemaking with the Department of Transportation.

On-road vehicles contribute more than 23% of total U.S. GHG emissions. 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.

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 U.S. and international scientists.

Scientific consensus shows that as a result of human activities, GHG concentrations in the atmosphere are at record-high levels, and data show the Earth has been warming over the past 100 years, with the steepest increase in warming in recent decades. The evidence of human-induced climate change goes beyond observed increases in average surface temperatures; it includes melting ice in the Arctic, melting glaciers around the world, increasing ocean temperatures, rising sea levels, acidification of the oceans due to excess carbon dioxide, changing precipitation patterns and changing patterns of ecosystems and wildlife.

Jackson and President Obama have publicly stated that they support a legislative solution to the problem of climate change and Congress’ efforts to pass comprehensive climate legislation. However, climate change is threatening public health and welfare, and it is critical that EPA fulfill its obligation to respond to the 2007 U.S. Supreme Court ruling.

EPA issued the proposed findings in April and held a 60-day public comment period. The agency received more than 380,000 comments, which were carefully reviewed and considered during the development of its final findings.