In its latest Airline Index released Thursday, Atmosfair said too little progress had been made by carriers around the globe to reduce their CO2 footprint.

The German climate protection group, which focuses on traffic, said airlines succeeded in reducing per-passenger and per-kilometer CO2 emissions by 2 percent within one year. But the organization warned that was not enough to compensate for the 4 percent rise in overall air traffic in the same period.

Hamburg-based aviation expert Cord Schellenberg said current low fuel prices were not conducive to raising airline's awareness of the need to cut back on harmful emissions.

"Because of the low fuel prices and expectations that this situation will not change any time soon, airline operators may well decide to keep older planes in their fleet longer than originally planned," he told the DPA news agency, adding that this would negatively impact the carriers' future CO2 emission levels.

More efforts underway

But a look at the order books of the world's major plane makers suggests there's no reason to panic. Both Boeing and its European rival Airbus have seen a steady rise in demand for more fuel-efficient aircraft.

The expected rise in air travel, however, is worrying to many climate protectionists. They suggest that one way to curb emissions would be to make airlines more efficient by increasing their load factor.

Emirates for instance is planning to refit its A380 jumbo jets for just two instead of three different passenger classes, thus providing room for 615 passengers per flight instead of only 500 - a 20-percent increase in capacity for roughly the same amount of fuel.

The Airline Index ranking pits big carriers against low-budget and charter airlines with all their different abilities to influence seating capacity and fuel efficiency.

For the first time, an airline reached the highest efficiency class. Tunis Air Express was able to achieve over 90 percent of the technically achievable potential on short-distance routes.

German flagship carrier Lufthansa improved its efficiency by 3 percent year-on-year, but because of its below-average seating capacity it only ended up in 68th position, with 190 airlines being surveyed by Atmosfair.

hg/cjc (Reuters, AFP)