LONDON (Bloomberg) — The UK Department of Energy and Climate Change said it will defend against a legal challenge by US airlines objecting to inclusion in the European Union's carbon dioxide emissions-trading plans.

"We are confident of the merits of the defence and intend to make a robust defence of the European legislation in the European Court," a government spokeswoman said in an e-mailed statement. She declined to be named, citing government policy.

The EU is adding airlines to its emissions-trading system, the world's biggest greenhouse-gas market, in 2012 to fight climate change. The system imposes a cap on industrial emissions of carbon dioxide, the main greenhouse gas blamed for rising temperatures. United Nations scientists say reductions in emissions are needed to keep the planet from overheating.

Jet planes, which account for five percent of UK emissions, could contribute 40 percent by 2050, depending on how fast the industry grows, according to Bruce Duguid, head of investor engagement at the Carbon Trust, a UK government-funded adviser on emissions policy. Airlines may need to spend as much as 35 billion euros ($50 billion) between 2012 and 2020 on carbon permits, Dugui said December 8.

AMR Corp.'s American Airlines, Continental Airlines Inc. and UAL Corp.'s United Airlines joined the Air Transport Association of America in a complaint last December, saying that inclusion of the aviation industry into the European's carbon trading programme "violated the US-EU bilateral Air Transport Agreement of April 2007 and the Kyoto Protocol," according to a London court filing.