Nothing would please me more than to see batteries break out of their traditional markets and propel our cars, a goal described in your News Feature 'Charging up the future' (Nature 456, 436–440; 2008). In my view, this will not happen, however, because of the weakness of electrochemical power storage. The best lithium-ion battery provides energy at the rate of 100 watt-hours per kilogram. For liquid fuels such as petrol and diesel the energy density is around 12,000 watt-hours per kilogram. Even after dividing the latter figure by four because of Carnot-cycle losses in the conventional car engine, you are still at least 30 times better off with petrol than with the best and most expensive battery.

Would people be willing to pay significantly more for cars that perform worse than current versions? How likely are they to charge their batteries with 'green' power, which costs up to 10 times more than conventional electricity? The truth is that electric cars may fill a niche market for idealistic commuters, but for longer trips they are out of the question.

Synthetic fuels made of non-edible biomass are the best way to free cars of carbon dioxide emissions with existing technologies. Although the enzymes needed for splitting cellulose into sugar (the source of ethanol) are still much too expensive, the Fischer–Tropsch technology for making synthetic fuels from waste wood, straw or grass has been around for 70 years. Controlled burning with the addition of water yields a mixture of carbon monoxide and hydrogen that can be catalytically converted into any desired liquid fuel suitable for conventional internal-combustion engines.

The infrastructure for distributing such fuels is already in place. And enough biomass grows each year to supply the world's entire car fleet.