On the large scale which applies to our common future – people and planet together – hydrogen is the only viable alternative. If you go back to the periodic table of all the elements, the only serious options are carbon and hydrogen. All carbon, whether from fossil fuels or from biomass, will simply disperse into the atmosphere when it is burned, in the form of carbon dioxide, the very gas whose presence in the atmosphere we are trying to reduce, not increase! When, by contrast, we burn hydrogen the only product is water vapour, which will simply re-enter the rain cycle from which it was extracted.