Passengers on two Hong Kong-based airlines are being given the chance to reduce their carbon footprint.

Fly Greener, a voluntary scheme launched by Cathay Pacific and Dragonair, invites passengers to make a cash contribution to offset the emissions of their flight, based on journey length and cabin class.

The program's first project is an investment in two wind power farms in Shanghai's Nanhui District and Chongming County.

An online calculator at www.cathaypacific.com and www.dragonair.com will work out the share of the carbon dioxide emissions created by each flight using fuel consumption data from the Cathay Pacific and Dragonair passenger fleet.

As an example, a passenger in economy class on a return journey from Shanghai to Hong Kong will create a carbon dioxide emission of 230 kilograms, which is worth HK$17.51 (US$2.24).

While carbon offsetting doesn't reduce emissions, it provides funding for projects that either remove greenhouse gases from the atmosphere or prevent emissions being released in the first place, said airline officials. "Passengers' contributions will be used to improve the local environment. The power generated at the wind farms is being fed into the Shanghai power grid."

They said wind farms had many benefits. "Unlike traditional coal-fired power stations, they don't produce the greenhouse gas carbon dioxide in the process of producing energy. Nor do they produce other pollutants that coal-burning does."

Most passengers had shown an interest in taking part.

"If the payment is not too high, I would like to put in my own effort," said a local office worker surnamed Liu, who is planning to travel to Hong Kong next month.