Under pressure from US states and environmental groups, the US Environmental Protection Agency will consider regulating CO2 and other emissions from aircraft engines. The agency published an advance notice of proposed rulemaking (ANPRM) on 11 July and will accept public comment for 120 days on the effects of climate change and the role of the Clean Air Act in regulating greenhouse gas emissions once the ANPRM is published in the Federal Register - likely to be around 28 July.
The Clean Air Act includes aircraft emission standards, covering pollutants criteria for air quality in localities, but its standards do not address CO2 and other greenhouse gases.
EPA administrator Stephen Johnson says the Clean Air Act is "the wrong tool" to address greenhouse gas emission since it would take decades to create a suitable framework and would result in "convoluted regulation". He says: "If the nation is serious about regulating greenhouse gases, we need Congress to act."
And US airlines are uncertain that either the EPA or the US Congress can effectively regulate aircraft emissions. Greenhouse gases are global, says Air Transport Association of America vice-president environmental affairs Nancy Young, but the Clean Air Act's regulatory mechanisms are focused on localities. She says regulating one source of emissions could affect other emissions and the economy.
"The real question is, is there a need to also set an aircraft engine standard for greenhouse gas emissions," Young says.
"We're already so motivated to minimise fuel burn. It's not clear you could do a better job with regulation without causing undue consequences."
In April 2007, the US Supreme Court ruled that greenhouse gas emissions could be regulated if the EPA determines they cause or contribute to air pollution that endangers public health.
Following the Supreme Court decision, the agency has been under pressure to propose regulations to control greenhouse gas emissions.
Five states, leaders from Washington DC and New York City and southern California's South Coast Air Quality Management District petitioned the EPA in December for federal regulatory standards for greenhouse gas emissions from commercial aircraft.
At the same time, Oakland, California-based law firm Earthjustice filed a separate petition that requested the EPA require reductions in greenhouse gas emissions from aircraft arriving in or departing from the USA.
Filed on behalf of environmental groups Friends of the Earth, Oceana and the Center for Biological Diversity, the petition also calls for the use of alternative fuels and more efficient aircraft design.