(Reuters) - Heavy industry groups and states argued in a federal court on Tuesday that U.S. environmental regulators had used faulty science in determining that greenhouse gas emissions endangered human health in the latest attempt to dismantle the Obama administration's rules on the emissions.
During the first of two days of arguments on a case that seeks to overturn Environmental Protection Agency regulations, Harry MacDougald, a lawyer for the petitioners, said uncertain evidence was used to reach "90 percent" certainty that human emissions are responsible for harmful climate change.
The three judges hearing the case appeared to resist deciding on whether the EPA's science was sufficient, with U.S. Circuit Judge David Tatel pointing out the agency had found the science certain enough.
"To win here, you have to make an argument that EPA's decision is actually arbitrary and capricious," Tatel said.
The coalition of power plants, business groups and 37 states also said a rule limiting carbon emissions from vehicles led to improper rules for power plants and other stationary sources.
The case stems from a 2007 Supreme Court ruling that greenhouse gases should be regulated under the U.S. Clean Air Act if the EPA determined them to be harmful to public health.
The agency found in 2009 that greenhouse gas emissions endangered the public. Environmental groups support the regulations since Congress failed to pass legislation to cap emissions.
Auto manufacturers, who already faced emissions standards in a handful of states including California, also support the national standards written by the EPA.
The EPA has said it relied on a variety of scientific reports to make the endangerment finding, including studies from a range of U.S. agencies.
Tuesday's arguments largely previewed the case the coalition will make on Wednesday that the EPA overstepped its power by applying the Clean Air Act only to the largest stationary sources of greenhouse gases such as power plants and big manufacturers, in a so-called "tailoring" rule.
"The core concern of these plaintiffs is about stationary sources and the tailoring rule," said Howard Fox, an attorney with Earthjustice, which supports the EPA's rules.
Analysts expect the big showdown to come on Wednesday, when the court will hear arguments on the tailoring rule. The rule was adopted so that small stationary polluters, such as schools, did not have to obtain permits for greenhouse gas emissions.
It was also aimed at reducing burdens on state and local government permitting agencies.
Critics argue that exempting some facilities from the rules represents a regulatory attempt to rewrite the Clean Air Act, which would have applied the emissions rules to those polluters.
Petitioners argued on Tuesday that the EPA should have anticipated the tailoring rule during the endangerment phase and taken into consideration the regulatory headache it would face when it had to apply emissions standards to non-vehicle sources.
The petitioners also argued that the tailpipe rule should have been delayed or rewritten to avoid having to tailor the rules for stationary polluters.
Peter Glaser, who argued on behalf of the petitioners, said the EPA ignored comments about stationary pollution sources while it was drafting the tailpipe rule, but said it was too late when petitioners tried to comment on the later rules.
"The analysis at the tailoring rule stage was limited by the fact that they had not considered this in the motor vehicle rule," he said during oral arguments.
EPA lawyers countered that the rulemaking process is established by law and that they were right not to look at stationary sources of pollution while writing the vehicle rules.
Reporting By Emily Stephenson; Editing by Bob Burgdorfer