It is almost 20 years since we should have started doing something about climate change. Instead, humanity has spent that time creating a monumental work of denial and procrastination. We have employed cod science, elaborated blame strategies, and generally messed around. Now, we are approaching the cliff edge.

Against this backdrop, the EU's package of climate and energy measures, agreed in principle last year, was a welcome sign we are at last moving from words to action. Even if the level of ambition is still inadequate, some parts of the plan have real bite - including a 20% target for renewable energy use, which could be the biggest move we have ever made towards a low-carbon economy.

But we are too often at the mercy of quack doctors peddling ineffective medicines with grim side effects. One element of the EU package - the aggressive promotion of liquid biofuel use in cars - falls squarely into this category.

Using plant materials to supply our energy needs is, in theory, a perfectly sensible idea - if it can be done in ways that maximise energy efficiency and minimise waste across existing production cycles - and we should be working out how to do this as quickly as we can.

But requiring 10% of the EU's transport fuel to come from biofuels in the next decade will not help. It will increase demand for conventional crops, push up food prices, and drive production into forests and grasslands, destroying precious wildlife and releasing stored carbon into the atmosphere.

Supporters of the 10% target claim it can be met through productivity increases and the use of "idle land". I recommend a browse round the EU website, where documents written by the very same people proclaim the benefits of the policy for European farmers, in higher commodity prices. Only since realising the embarrassing impacts of such a tactic on the poor have its architects fallen back on promises of technical advance.

Arguing that the target could be met through productivity increases is very different from ensuring it will be. The latter would require stringent regulation of the global agricultural commodities market - an implausible project that would be opposed with vigour, by the EU's trade commissioner and the World Trade Organisation.

Rather than crossing our fingers and hoping that the current policy is not a disaster, we should scrap it and get on with designing policies that promote the efficient use of bioenergy as part of a wider strategy, built around the cheapest, safest and most sustainable options for reducing emissions.

Those options do exist. It is technically feasible to build cars that emit about 80 grammes of CO2 per km - half that of the average family saloon. Why, then, are European policies on vehicle efficiency so lacking in ambition? The answer is: they are designed to protect the interests of the car industry, rather than protect the world's poor or its biodiversity.

Behind all the arguments about biofuels, there is a moral choice. High food prices punish the less well off. Smaller cars with more efficient engines and lower fuel costs, coupled with a move away from policies that increase food prices, are, on the other hand, truly socially progressive. How we go forward from here, will depend largely on Gordon Brown, because without the UK's intervention there is no chance that Europe will step away from the 10% target.

This week is the last chance Europe has to rethink its policy. So, Mr Brown, are you going to go to demand more efficient cars, or will you rubber stamp an EU policy that will force consumers to burn the world's food supplies and forests in their petrol tanks?

· Ruth Davis is head of climate change policy at the RSPB