WASHINGTON - The US Supreme Court considers on Monday whether President Barack Obama's administration overstepped its authority by imposing new regulations to reduce pollution in response to climate change.
In a 90-minute oral argument, extended from 60 minutes because many parties are involved, the justices will examine a relatively narrow challenge by industry groups and Republican-leaning states to one aspect of a suite of regulations issued by Obama's Democratic administration in 2009 and 2010.
The regulations represent the first major federal effort to tackle greenhouse gas emissions that scientists say are the driving force behind climate change.
Obama has been going it alone on climate change, largely because of opposition from Republicans and some Democrats in Congress. The Clean Air Act has been the Environmental Protection Agency's main tool for addressing emissions since the US Senate rejected a cap-and-trade bill in 2010.
The nine justices will weigh whether the agency has authority to regulate greenhouse gases under a programme for issuing permits for stationary sources of pollution, such as power plants and oil refineries. A decision is expected by the end of June.
When it agreed to hear the case in October, the court declined to consider several broader questions that would have more directly attacked the authority of the EPA in its regulation of greenhouse gases.
By declining to hear those questions, the court indicated it was unlikely to revisit a landmark 2007 case, Massachusetts v. EPA, when it held on a 5-4 vote that carbon was a pollutant that could potentially be regulated under the air pollution law.
The ruling is unlikely to have a broad impact on the administration's climate strategy, including plans to introduce greenhouse gas standards for new power plants under a separate provision of the Clean Air Act. The standards were announced in September but have yet to be formally issued.
By June the agency is expected to unveil more emissions standards for existing power plants. Power plants account for roughly 40 per cent of domestic greenhouse gas emissions.
The single question the high court agreed to hear was one of many raised by nine different coalitions of industry groups, such as the American Petroleum Institute, and 16 states, including Texas and Virginia.
"We remain concerned that if the EPA continues to stretch the boundaries of the Clean Air Act and apply it to greenhouse gases, it could have dire consequences for our members," said Ross Eisenberg, the vice-president for energy and resources policy at the National Association of Manufacturers, which is one of the challengers.
In June 2012, an appeals court in Washington upheld all the regulations, prompting challengers to seek high court review.
Although there are various ways the court could rule, a loss for the EPA could remove a whole category of pollutants, not just greenhouse gases, from the so-called "prevention of serious deterioration" or PSD programme, which requires any new or modified major polluting facility to obtain a permit before any new construction is done if it emits "any air pollutant."
Under the programme, the operators have to show they are using the best available technology available to reduce emissions of the covered pollutants. So far, 335 facilities have applied for permits that include greenhouse gas requirements, an EPA official said.
The regulations are being defended not just by the administration but also by 15 states and various environmental groups. One utility, Calpine Corp, which operates natural gas and geothermal plants, also backed the government by filing a friend-of-the-court brief saying the regulations are not a heavy and costly burden.
Sean Donahue, a lawyer representing environmental groups in the case, said removal of greenhouse gases from the permitting programme would lead to more emissions and discourage innovation on new pollution control technology.
"It's quite important because we are at this early stage of greenhouse gas regulation and we need to keep forward momentum," Donahue said.
The case is Utility Air Regulatory Group v. EPA, US Supreme Court, No. 12-1146.