I don't blame Mo Farah, Pele and Haile Gebrselassie, who lined up, all hugs and smiles, outside Downing Street for a photocall at the prime minister's hunger summit. Perhaps they were unaware of the way in which they were being used to promote David Cameron's corporate and paternalistic approach to overseas aid. Perhaps they were also unaware of the crime against humanity over which he presides. Perhaps Cameron himself is unaware of it.

You should by now have heard about the famine developing in the Sahel region of west Africa. Poor harvests and high food prices threaten the lives of some 18 million people. The global price of food is likely to rise still further, as a result of low crop yields in the United States, caused by the worst drought in 50 years. World cereal prices, in response to this disaster, climbed 17% last month.

We have been cautious about attributing such events to climate change: perhaps too cautious. A new paper by James Hansen, head of Nasa's Goddard Institute for Space Studies, shows that there has been a sharp increase in the frequency of extremely hot summers. Between 1951 and 1980 these events affected between 0.1 and 0.2% of the world's land surface each year. Now, on average, they affect 10%. Hansen explains that "the odds that natural variability created these extremes are minuscule, vanishingly small". Both the droughts in the Sahel and the US crop failures are likely to be the result of climate change.

But this is not the only sense in which the rich world's use of fuel is causing the poor to starve. In the United Kingdom, in the rest of the European Union and in the United States, governments have chosen to deploy a cure as bad as the disease. Despite overwhelming evidence of the harm their policy is causing, none of them will change course.

Biofuels are the means by which governments in the rich world avoid hard choices. Rather than raise fuel economy standards as far as technology allows, rather than promoting a shift from driving to public transport, walking and cycling, rather than insisting on better town planning to reduce the need to travel, they have chosen to exchange our wild overconsumption of petroleum for the wild overconsumption of fuel made from crops. No one has to drive less or make a better car: everything remains the same except the source of fuel. The result is a competition between the world's richest and poorest consumers, a contest between overconsumption and survival.

There was never any doubt about which side would win.

I've been banging on about this since 2004, and everything I warned of then has happened. The US and the European Union have both set targets and created generous financial incentives for the use of biofuels. The results have been a disaster for people and the planet.

Already, 40% of US corn (maize) production is used to feed cars. The proportion will rise this year as a result of the smaller harvest.

Though the market for biodiesel is largely confined to the European Union, it has already captured 7% of the world's output of vegetable oil. The European commission admits that its target (10% of transport fuels by 2020) will raise world cereal prices by between 3% and 6%. Oxfam estimates that with every 1% increase in the price of food, another 16 million people go hungry.

By 2021, the Organisation for Economic Co-operation and Development says that 14% of the world's maize and other coarse grains, 16% of its vegetable oil and 34% of its sugarcane will be used to make people in the gas-guzzling nations feel better about themselves. The demand for biofuel will be met, it reports, partly through an increase in production; partly through a "reduction in human consumption". The poor will starve so that the rich can drive.

The rich world's demand for biofuels is already causing a global land grab. ActionAid estimates that European companies have now seized 5m hectares of farmland – an area the size of Denmark – in developing countries for industrial biofuel production. Small farmers, growing food for themselves and local markets, have been thrown off their land and destituted. Tropical forests, savannahs and grasslands have been cleared to plant what the industry still calls "green fuels".

When the impacts of land clearance and the use of nitrogen fertilisers are taken into account, biofuels produce more greenhouse gases than fossil fuels do. The UK, which claims that half the biofuel sold here meets its sustainability criteria, solves this problem by excluding the greenhouse gas emissions caused by changes in land use. Its sustainability criteria are, as a result, worthless.

Even second-generation biofuels, made from crop wastes or wood, are an environmental disaster, either extending the cultivated area or removing the straw and stovers which protect the soil from erosion and keep carbon and nutrients in the ground. The combination of first- and second-generation biofuels – encouraging farmers to plough up grasslands and to leave the soil bare – and hot summers could create the perfect conditions for a new dust bowl.

Our government knows all this. One of its own studies shows that if the European Union stopped producing biofuels, the amount of vegetable oils it exported to world markets would rise by 20% and the amount of wheat by 33%, reducing world prices.

Preparing for the prime minister's hunger summit on Sunday, the international development department argued that, with a rising population, "the food production system will need to be radically overhauled, not just to produce more food but to produce it sustainably and fairly to ensure that the poorest people have the access to food that they need". But another government department – transport – boasts on its website that, thanks to its policies, drivers in this country have now used 4.4bn litres of biofuel.

Of this 30% was produced from recycled cooking oil. The rest consists of 3bn litres of refined energy snatched from the mouths of the people that Cameron claims to be helping.

Some of those to whom the government is now extending its "nutrition interventions" may have been starved by its own policies. In this and other ways, David Cameron, with the unwitting support of various sporting heroes, is offering charity, not justice. And that is no basis for liberating the poor.

• For a fully referenced version of this article, visit George Monbiot's website