Having been ordered by the Supreme Court to decide whether greenhouse gases are a threat to human health and welfare, U.S. EPA came up with a system of emissions curbs that are "fair, feasible and faithful to the agency's duties," lawyers from the Justice Department told a federal court today as the sprawling litigation moved into the meat of the issue.

The brief, filed with the U.S. Circuit Court of Appeals for the District of Columbia this afternoon, defends the "endangerment" finding made in late 2009 by Administrator Lisa Jackson, which laid the foundation for new standards for carbon dioxide emissions from cars and trucks and triggered the first-ever limits on greenhouse gases from power plants and other large industrial plants.

That finding has drawn dozens of challenges from high-emitting industries, libertarian think tanks and Republican-led states that see the new rules as a hindrance to the economy.

They have questioned in their court filings that humans are changing the climate, as nearly all mainstream scientists agree. One of the briefs, submitted by Virginia Attorney General Kenneth Cuccinelli (R), says that EPA should have rethought its finding in light of the "Climategate" episode, in which emails were taken from a server at the University of East Anglia's Climatic Research Unit in the United Kingdom (Greenwire, May 23).

But the Obama administration relied on "thorough and peer-reviewed assessments of climate change science" from the U.N.-affiliated Intergovernmental Panel on Climate Change, the U.S. Global Change Research Program and the National Research Council, says today's filing, which is signed by Ignacia Moreno, head of the Justice Department's Environment and Natural Resources Division.

It says those reports provide clear evidence that man-made emissions are affecting the planet -- and given that evidence, that the court should defer to the expertise of agency scientists.

"Adverse public welfare effects observed to date and projected to occur in the future include increased drought, sea level rise, harm to agriculture, and harm to wildlife and ecosystems," the filing says. "The administrator found that the balance of evidence in every area considered provides support for an endangerment finding to public welfare."

Briefing on the climate rules will continue through the end of the year. EPA is scheduled to defend its rules for cars in a Sept. 1 brief and follow that up with a defense of the rules for industrial plants on Sept. 16.

Click here to read the brief.