The United States yesterday gave warning that European plans to impose a carbon tax on airlines would be challenged in court.

America has been stung by European criticism, led by Britain, that it should accept binding cuts in CO2 emissions because it is doing too little to fight global warming. But the US hit back yesterday by accusing the EU of focusing on airline emissions when road transport accounted for a much higher share of pollution.

The row came as President Bush prepares for his own two-day meeting on climate change this week in Washington. The United Nations also debated the issue on Monday in New York.

European leaders have agreed to impose a “cap and trade” system on all airlines flying through EU airspace from 2012, obliging them to buy extra carbon credits if their aircraft exceed strict limits. Any cuts in emissions through cleaner fuel or aircraft would give a surplus of carbon credits, which could be sold to higher polluters.

“We do not think that Europe has the authority to do it,” C. Boyden Gray, the US Ambassador to the EU, said yesterday. “You do not need to add any incentives to airlines to increase fares. I think it is going to end up in the courts . . . I do not see how it is going to get resolved politically.”

On Monday Hilary Benn, the Environment Secretary, singled out the US in a call for rich countries to accept binding targets.

The 27 nations of the EU have agreed to cut CO2 emissions by 20 per cent by 2020 and by 30 per cent as part of a wider international deal if one can be reached. President Bush favours voluntary, sector-by-sector targets and has set a goal for reducing road transport emissions, something that the EU has so far not agreed, although it is debating emission rules for new cars.

Mr Gray added: “Ninety per cent of the transport sector is cars, trucks and buses. High oil prices and tax do not seem to have reduced CO2. It is the fastest-growing sector in the EU and US and . . . you ought to tackle that.”

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