The (red) hydrogen proton breaking away from the main atom

Researchers in Vancouver, Canada, are already testing an electric bus powered by a 'fuel cell'.

They hope it will eventually replace the internal combustion engine which is responsible for creating two-thirds of global warming gases.

Fuel cells are not a new technology, but have so far only been used in space.

Fuel Cells are made up of two plates with a membrane in the middle. Oxygen is fed in from one side, hydrogen from the other. The two gases naturally want to combine, but the membrane will only allow part of the hydrogen atom, the proton, to pass through. The rest of the hydrogen atom, the electron, has to go round to the oxygen side via an external circuit, creating electricity.

BBC reporter Clive Myrie enjoys a glass of fuel cell emissions

The hydrogen and oxygen eventually mix to form water.

However there is a drawback at the moment - the cost. Fuel cell vehicles currently cost more than $1m to build.

But car companies like Ford and Chrysler-Daimler are investing millions in developing fuel cell technology for road vehicles.

The experimental bus ....

Ford is working with the Canadian company Ballard Power Systems, whose spokesman Mossadiq Umedally says they are working to bring the cost down.

... could stop pollution like this

"They are seen as aerospace which means they are very expensive and not available for commercial applications.

"Ballard was one of the first to pick up the mantle and take this technology and say how can you make it really cheap, how can you make it really powerful so you can make it fit under the hood of a car."

William Boei, of the Vancouver Sun, points out that there is another snag, "putting together the infrastructure for the fuel, in that at this point you can't drive to your corner gasoline station and fill up with hydrogen or methanol".

But those researching fuel cell technology believe that by 2005 they will have reduced costs enough to make it commercially viable.