Airbus says its newborn giant will be far more fuel efficient than Boeing's 747, a jetliner whose basic design goes back 35 years, and thus by carrying more passengers farther per litre (gallon) of kerosene burned, it is doing the planet a favour.

But French expert Jean-Marc Jancovici says that such calculations "fail to give the full picture" when it comes to carbon pollution.

Jancovici, author of numerous books on climate change and who runs a well-regarded website (manicore.com) on global warming phenomenon, says that if Airbus' business plan is right, "the number of air passengers will triple in the next 20 years."

Even if planes get bigger, there will still be a lot more of them in the skies in order to meet demand and this will cancel out the benefits in improved fuel efficiency, he told AFP.

Jancovici drew a parallel with car pollution. In the past two decades, pollution standards for cars have become progressively tougher. But so many more cars have flooded onto the road in the meantime that the annual volume of pollution remains unchanged.

Airbus says the A380 offers a gain in fuel use of some 15 percent when compared with Boeing's top-of-the-range 747-400.

At a cruising speed of 900 kilometers (550 miles) per hour, the A380 delivers a consumption of three litres (5.4 pints) of fuel per passenger per 100 kms (62 miles) travelled, according to Airbus. It cites a figure of 3.4 litres (6.2 pints) for the 747-400.

Jancovici says the gain may be an improvement "but it is obviously not a solution" if the new generation of aircraft continues to burn a dirty fuel and more and more of the planes take to the skies.

"Instead of increasing pollution, scientists say that the world will have to reduce its emissions of greenhouse gases by three-quarters just to stabilise the climate system," he says.

UN experts, in a series of reports published in 2001, estimated that the world's average temperature will rise by between 1.4 and 5.8 C (2.5 to 10.4 F) by the end of this century, as heat from the Sun is trapped by carbon gases spewed out by coal, gas and oil.

Aircraft currently account for 2.5 percent of emissions of carbon dioxide (CO2), the principal greenhouse gas.

This figure may look small, but it is deceptive, says Jancovici. Air transport accounts for a very small part of the global economy in proportion to its far bigger environmental cost.

In addition, because aircraft emit their pollution at altitude rather than at ground level, the effect as an amplifier of global warming can be five times worse than that of a truck.

Compounding the problem is that the aviation business is so far immune from global-warming regulations demanding higher fuel efficiency or lower pollution, and kerosene, a highly polluting fuel, is untaxed.

According to a report published last month by the French Institute for the Environment (IFEN), a passenger travelling by airliner emits 40 percent more CO2 per km (mile) than when travelling by car, a figure calculated on the basis of 1.8 persons per vehicle.

Just flying from Paris to New York and back is the equivalent to a quarter of annual French per-capita emissions.

The problem is bound to get worse as low-cost airlines make air travel more widely accessible, says the study's author, Michel Hubert.

He estimates that if passenger traffic rises just five percent annually, CO2 emissions by the aviation business will surge by 240 percent over the next 30 years.

"The improvements in energy efficiency achieved are seemingly not sufficient to prevent a significant increase in the impact of air transport and climate change," Hubert concludes gloomily.

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