As oil prices continue to rise, thoughts naturally turn to replacements. Many people talk about electric or hydrogen vehicles as being the way of the future, since they do not rely on fossil fuels such as oil. (This is straying a little beyond my area of expertise, but here are some thoughts anyway.)

To my mind, such comments ignore an absolutely fundamental question: where does the electricity or hydrogen come from? At the moment, a large proportion of our electricity is produced by burning fossil fuels and so switching from petrol cars to electric cars is of very little benefit. The same applies to hydrogen, which can either be made from water using electricity, or by splitting a hydrocarbon fuel such as natural gas (CH₄). In either case the losses through the various conversions are so high that it would be more efficient to simply burn the fossil fuel directly in the vehicle, as is done today. There are also severe difficulties with storage of both hydrogen and electricity in sufficient quantities to give a useful driving range.

It is true that hydrogen or electric cars produce no toxic emissions at the point of use, but it is already possible to reduce the toxic emissions of conventional vehicles to levels where they cease to be an important factor. Even with increasing traffic levels, ever-tighter emissions standards mean that urban air quality is actually improving in most of the developed world, and there is no reason why this should not continue. The very high cost and poor efficiency of electric or hydrogen vehicles does not seem a price worth paying for marginal additional air quality improvements.

Of course, at some point we may well have a cheap, environmentally friendly way to produce electricity, at which point hydrogen or electric vehicles will be appropriate. But all the current candidates have significant problems - renewables such as tidal and wind power are expensive and intermittent, while nuclear has issues with safety and waste disposal. Clearly these technologies should continue to be pursued, and hopefully the problems will be solved. But until they are, hydrogen and electric vehicles as a solution to environmentally-friendly travel are just an illusion.

In my view, further optimisation of conventional vehicles (as discussed here) is the most effective medium-term strategy. People have been predicting the imminent death of the internal combustion engine for decades, but I believe it still has many years to live. We may well see substution (in whole or in part) of oil-derived fuels by biomass-derived ones - for example ethanol from sugar cane - as a medium-term solution. It is unfortunately true that, if you were to sit down and design the "ideal" fuel for a vehicle (in terms of ease of handling, energy density, etc) you would almost certainly end up with something like petrol or diesel.

Note: I am not any kind of expert on energy generation, and am not qualified to comment on the relative merits of wind, wave, nuclear, etc. It is however clear to those who work in this field that all these technologies have severe practical problems, and cannot be expected to provide all our energy needs in a CO₂-free way for years or even decades to come.