It's a known fact that frequent flyers -- in addition to racking-up those handy little miles -- damage the environment.

Air travel has increased five-fold since 1970, with much of that growth taking place in the last few years due to the increasing popularity of budget airlines. However, as the cost of tickets continues to decline, it has become increasingly clear that bargain prices do not account for the damage a single flight does to the environment.

Environmental groups say such air travel is a climate catastrophe in the making, since airplanes emit three times the amount of greenhouse gases that automobiles do. The no-frills travel boom, according to Germany’s green lobby, is the country’s “Number one climate killer ”.

Climate change, caused by greenhouse gases such as carbon dioxide, is deemed by many experts to be the biggest long-term threat to mankind. They predict rapidly rising temperatures prompting higher sea levels, devastating floods and droughts.

The United Nations Intergovernmental Panel on Climate Change estimates aviation causes 3.5 percent of man-made global warming and that figure could rise to 15 percent by 2050.

Efforts to impose a tax on jet-engine fuel have been unsuccessful, and, thus far, the issue has not been addressed in the Kyoto Protocol, the international treaty aimed at preventing climate change. But now, a German environmental initiative, Atmosfair, hopes to encourage travellers to strike the right balance on a voluntary basis.

Making-up the difference

The idea is simple: those who fly will make a contribution to finance an environmental project in a developing country.

The idea occurred to Germany's environmental minister, Jürgen Trittin, when he attended the United Nations' Conference on Environment and Development in 2002.

"We were trying to think of a way we could credibly attend the conference, given the fact that the transport of our delegation would result in 1280 tons of greenhouse gas," said the minister. Of course, that would have to be made-up elsewhere, says Trittin, so he and and his ministry financed a row of ecologically sensitive homes in a township.

The concept has now been adopted on a larger scale by Atmosfair, which is run by Klaus Töpfer, the director of the United Nations' environmental program. Töpfer doubts every flight guest will voluntarily contribute his or her share, but he hopes the project will create a greater awareness.

"The costs must be carried by someone," he told Deutsche Welle, "And in general, we pawn them off on those living in considerably poorer countries and on future generations."

The sponsor of the effort is the "Forum for a Different Kind of Travel", an umbrella organization of 100 environmentally aware travel agencies with 60,000 customers per year, half of whom are frequent flyers.

That'll be €74.70 to Nairobi and back, please

The Forum has worked out a table, which can be used to calculate in euros the approximate cost of -- if one can quantify such things in money -- air travel of varying lengths does to the environment.

For example, a flight from Berlin to Bonn and back -- according to the table -- costs €8. A flight from Berlin to Nairobi, including a change in Frankfurt, creates 4260 kilograms of carbon monoxide. Converted into euros, that comes to €74.70.

Ideally, airline passengers will calculate these expenses and contribute some or all of the sum towards the environmental projects sponsored by the forum, including the construction of solar community kitchens in India and an environmentally-friendly factories in Brazil.

Töpfer, for one, has promised to make contributions for all of his flights this month, and considering how often this U.N. official jets around the world, that's quite a bit.