Carbon offsetting allows air passengers to negate the effect of their flight on the environment by contributing to green projects such as tree planting or the retirement of carbon credits for polluting industries.

However, Aer Arann chief executive Garry Cullen said the airline will not start buying offsets until the European Regions Airline Association (ERAA) introduces a Europe-wide offset scheme for regional airlines.

"We want to understand fully what carbon dioxide emissions we have and get it officially measured before we get involved in trading, " he said.

Cullen also said consumers were starting to become confused by the rival green claims made by Irish airlines. Both Aer Arann and Ryanair claim to be Ireland's greenest airline.

"There is a risk and I suppose it's because all carriers are trying to be seen as more green. The industry has become very reactive because there so much hysteria around aviation emissions, " he said.

However, Cullen repeated Aer Arann's claim that it is the greenest airline because "our turbo-prop aircraft are ideally suited for the market we're in and it avoids flying gas guzzling jets when demand is low, and they also burn less fuel."

Meanwhile, at its results presentation last week, Ryanair, which has rejected the concept of carbon offsetting, produced a table using data from an unnamed Dutch consumer organisation seemingly showing that it was 'Europe's greenest airline'. The data, however, included only airlines that operate mainly jet aircraft.

The chief executive of the Consumer Association of Ireland (CAI), Dermott Jewell, said an urgent Europe-wide investigation into airlines' claims was needed.

"The difficulty here is that consumers may not be as informed as they should be, and in Ireland it seems they are accepting the claims of airlines that do not meet the standards of airlines in other jurisdictions, which offer services like carbon offsetting, " he said.