The problem with aviation is the rate at which it is growing, according to Dr Alice Bows, a leading UK expert on global warming.

Dr Bows said Ryanair's Michael O'Leary is probably correct when he says aviation only accounts for 2 per cent of global carbon emissions. However, that is set to change radically unless measures are taken.

The senior research fellow at the Tyndall Centre for Climate Change, in Manchester, told The Irish Times that with aviation growing at a greater rate than any fuel efficiency measures it can introduce, and with governments seeking to reduce carbon emissions from all sectors, aviation is set to become responsible for a greater and greater level of overall carbon emissions.

A recent paper by Dr Bows and Kevin Anderson estimated that given the UK's targets for carbon emission reduction, and the projected growth in aviation, the sector is set to account for more than a quarter of the UK's contracting "carbon budget" or target carbon allocation by 2050.

The above is a best-case scenario. Other ways at looking at the same figures arrive at a figure of up to 50 per cent of the total quota, according to the paper.

If the more ambitious targets that scientists say are necessary to prevent "dangerous climate change" are factored in, the situation is even more stark.

This sees aviation using up the UK's entire emission quota by 2050. O'Leary has rightly stated that his airline has a particularly good record on emissions.

A combination of factors are involved in Ryanair's impressive fuel efficiency statistics. Ryanair has a relatively new fleet of aircraft, with greater than average fuel efficiency. It flies point to point and lands at smaller airports, so spends less time running engines while waiting to take off or land. Also, it has relatively high occupancy rates.

The airline's website, in a section on Ryanair and the environment, boasts that its fuel-burn per "revenue passenger kilometre" has dropped by almost 52 per cent since 1998.

That is all well and good but the same website records another statistic which shows where the difficulty lies. Ryanair's passenger numbers have grown from 4.6 million in 1998 to 40 million last year. In other words, even taking the impressively increased fuel efficiency into account, total carbon emissions by Ryanair have grown hugely since 1998. (By a factor of 8.7, if The Irish Times has done its sums right).

Ryanair is growing faster than most airlines, but air travel generally is growing throughout Europe at a pace greater than the increases in fuel efficiencies being introduced by aircraft manufacturers.

Also, low-cost travel is growing at a faster rate than air travel generally.

"In the UK, average fuel efficiency is going up by 1 or 2 per cent per year, but growth is moving by 7 to 8 per cent per year," said Dr Bows. Dr Bows's paper showed that the British government's targets for carbon emission reductions are in conflict with its plans for a growing aviation sector. The same may be the case for Ireland, where massive projected growth in aviation is also being catered for.

Carbon emissions from the aviation sector were not factored into the Kyoto targets for reasons that included the difficulty in allocating emissions to nations when international flights are involved. However, the European Commission has now set out to address the issue.

The Environmental Protection Agency says international aviation emissions attributable to Ireland have gone from 1 million tonnes in 1990 to 2.4 million tonnes in 2005. Continuing growth is expected, as can be inferred from the plans of our major airports.

Cork airport, which handled three million passengers last year, has just opened a new terminal with a capacity to handle up to five million. Shannon airport handled 3.6 million passengers last year and expects to handle five million by 2014.

Dublin airport handled an estimated 21.3 million passengers in 2006 and expects to handle approximately 26 million by 2009.

In other words, growth is shooting ahead aided by publicly funded infrastructure while at the same time pressures are growing for the Government to finally act on the global warming issue.

Something has to give.