Scandinavian Airlines is allowing passengers the opportunity to pay a voluntary greenhouse fee to offset their flight's carbon dioxide emissions.

Money generated from the carbon offset program will be used to fund environmental projects through the CarbonNeutral Co.

The airline said a passenger travelling between Stockholm and continental Europe would pay about 4.50 euros, or $7, in carbon offset fees. A person travelling a longer distance, from Stockholm to New York, would pay about 20 euros or about $31.

SAS, which operates Blue1, Spanair, SAS Braathens, Wideroe, airBaltic and Estonian Air, said the program is part of its environmental strategy. By 2011 the European Union will require all airlines flying within the bloc to trade carbon allowances.

'Carbon neutral' 2006 word of the year

Carbon offset programs have grown in popularity in recent years to such an extent that the New Oxford American Dictionary chose the phrase "carbon neutral" as its word of the year in 2006.

'It's more than a trend, it's a movement.'—New Oxford American Dictionary

"Being carbon neutral involves calculating your total climate-damaging carbon emissions (your 'carbon footprint'), reducing them where possible, and then balancing your remaining emissions, often by purchasing a carbon offset: paying to plant new trees or investing in 'green' technologies such as solar and wind power," Oxford University Press said in a release.

"It's more than a trend, it's a movement, which is why the editors of the New Oxford American Dictionary have declared carbon neutral the word of the year for 2006."

Critics of the programs say they're a means of assuaging consumer and company guilt with monetary contributions. But advocates say carbon trading programs encourage consumers to be mindful of their carbon footprint. They also note that offsets neutralize damage through energy projects including wind farms, tree planting and methane capture plants.

With files from the Associated Press