Many agree that replacing conventional petrol driven cars with hydrogen is a good idea provided the hydrogen does not originate in a process involving oil as the only product from hydrogen burning is water, rather than carbon dioxide.

However the road to hydrogen-powered vehicles will not be easy, industry experts state. Representatives of European and American car and energy companies at the National Hydrogen Association convention said hydrogen technology is feasible, but faces big challenges to become commercially viable.

"We all have our homework to do in the coming years," said Klaus Bonhof, manager of the alternative fuels division of DaimlerChrysler AG. "We must produce technology viable in volume, and that technology must be commercially applicable."

Several car compnaies had hydrogen-powered vehicles on display at the conference, but all have similar technological challenges, including costs that range up to a million dollars a piece and limited range on a hydrogen fill-up. While a hydrogen-pwered car can travel 45 to 50 miles on a gallon, the fuel tank only provide a range of 125 to 150 miles. This is because hydrogen is put in a car as a liquid at very low temperatures, but reverts to a gas as on warming. The gas produced has to be vented while the car is not being used so that after a few days the tank will be empty.

The industry is working on this and BMW vice president of clean technology Frank Ochmann said BMW is testing an insulated tank that would keep hydrogen cold and liquid. "If you put in this tank a snowman, it would take about thirteen years to melt down," he said.

Developing hydrogen fuel station is easy part, experts said as hydrogen is already shipped to industrial users in tanks or moved through pipelines. BMW estimates it will be 2025 before hydrogen powered vehicles are commonly produced and sold.

The observation that soot makes global warming "worse" is well covered today. The BBC covers this - largely because it appears that soot is more important for global warming than realised earlier. Dr James Hansen and Larissa Nazarenko, (Goddard Institute for Space Studies, NASA, and Columbia University Earth Institute) suggest that trying to reduce the amount of soot produced would be easier than cutting carbon dioxide and other greenhouse gas emissions. Concentrations of soot are often high over China and India, where coal and organic fuels are used domestically, and over Europe and North America, where the main source is diesel oil.1

• 1. Soot climate forcing via snow and ice albedos,
  Hansen, J.
  , Proceedings of the National Academy of Sciences, 01/2004, Volume 101, Issue 2, p.423 - 428, (2004)