Meaningful CO2 reduction will be no walk in the park for U.S. consumers and businesses.

In a decision which has wide-ranging and potentially negative consequences for the stumbling U.S. economy, the Environmental Protection Agency officially ruled this morning that greenhouse gases (GHGs) threaten the public health and welfare of the American people.

The final ruling was not surprising given previous public statements of President Obama and his political appointees.

EPA also found that GHG emissions from on-road vehicles contribute to that threat.

Since virtually all vehicles for the near or longer term, will burn fuels that cause large amounts of GHGs, more stringent fuel economy standards are inevitable. This will affect the types, sizes and cost of vehicles —  in ways yet unknown — that  you will be able to buy.

EPA’s final findings were issued in response to a 2007 U.S. Supreme Court decision that GHGs fit within the Clean Air Act definition of air pollutants. Prior to that, under Republican Administrations, the EPA did not take regulatory action to deal with the controversial problem.

While the findings do not impose any emission reduction requirements, they clearly are part of the legal process needed to all allow 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.

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

The proposed national emissions program would require model year 2016 vehicles to meet an estimated combined average emission level of 250 grams of carbon dioxide per mile. The overall light-duty vehicle fleet would reach 35.5 miles per gallon (mpg) in model year 2016, if, big if, all reductions were made through fuel economy improvements.

However, just how the final fuel economy and GHG rules are written — and what credits, exemptions or other loopholes are given automakers, who are currently furiously lobbying behind the scenes — could drastically reduce the projected reductions, which frankly  serve political needs both in the U.S. and globally.

Current EPA methodology allows fuel economy ratings for compliance purposes at 25% or more above the fuel economy sticker posted on new vehicles. If this continues under the new rules yet to be published, the proposed 35.5 mpg 2016 standard would actually be met by the sale of vehicles that achieve in use far less than that. GM’s Chevrolet Volt, rated at 230 mpg under proposed EPA methodology, and other electric vehicles will likely be used to offset the sales of guzzlers.

“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,” said EPA Administrator Lisa P. Jackson.

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  analysis for decades by scientists in the United States and around the world.

While the focus in the U.S. has been the debate around CO2, nitrous oxides — a significant by-product of  combustion in diesel engines — require costly after treatment methods to comply with current standards. Future U.S. rules will likely restrict the sales of fuel-efficient diesel engines that European makers in particular are counting on to meet increasingly stringent  fuel economy requirements.

The announcement comes, not coincidentally in my view, as another, yet another, international climate change meeting opens in Copenhagen today. President Obama will appear in Copenhagen at the close of the talks on December 18 when world leaders arrive to present what agreements, if any, have been reached by diplomats on reducing greenhouse gas emissions.

Heretofore, emerging nations have balked at imposing controls since it would restrict their economic growth at a time when their economies are burgeoning.

The stark fact remains that energy use is also directly related to the production of wealth, as well as GHGs. Moreover, the debate will and should continue as to what effects new regulations will have on the U.S. economy, which is in the worst shape since the Great Depression.