Biofuel research should focus on planes and not cars, the think tank Policy Exchange has said.

智囊团Policy Exchange表示，生物燃料的研究应该主要针对飞机而非汽车。

Virgin¹ Atlantic are among airlines to trial flight powered by biofuel" width="226" border="0" src="/upimg/090722/4_062142_1.jpg" />
Virgin Atlantic are among airlines to trial flight powered by biofuel

A crop area the size of the USA would be needed to biofuel all the world's cars and alternatives, such as electricity, exist for them, it added.

Instead, it said the EU should fund research into using plant-based fuel for aviation（航空） to help cut emissions².

Sceptics say some biofuels create more carbon than they save and push up the price of food for the poor.

Most biofuels are derived³ from（来源于） crops such as corn, sugarcane（甘蔗） and rapeseed（油菜籽）.

Bioethanol（生物乙醇） is usually mixed with petrol, while biodiesel（生物柴油） is either used on its own or in a mixture.

The UK government, which is funding a £27m research centre to find economically viable⁴ alternatives（可行的选择） to fossil fuels, says 25% of greenhouse gas emissions come from transport.

In April 2008, it introduced a "Renewable Transport Fuel Obligation", requiring 2.5% of all fuel sold at petrol stations to be biofuels, having revised its target from 5%.

Escalating⁵ emissions

The EU also changed its stipulation⁶（约束，约定） that 10% of transport fuel had to be from crop-based fuel, instead saying the targets could be met by any renewable source, including fuel cells, hydrogen or solar power.

Policy Exchange has previously⁷ said the government should spend its £550m annual biofuel subsidies⁸（补助金，津贴） on halting the destruction of rainforests and peatland（泥炭地）, which remove carbon dioxide from the atmosphere.

Now the centre-right think tank says the EU should switch policy to subsidising development of biofuels for aviation because planes cannot run on other sources of energy.

Airlines including Virgin Atlantic have trialled flights using up to 20% biofuel to power the engines, although climate change campaigners say use of the fuel is not sustainable.

Policy Exchange claims using biofuels is the only way in the foreseeable future to meet people's desire to travel without escalating（扩大，升高） emissions of greenhouse gases.

Airlines should be mandated⁹（委托统治的） to blend biofuel with kerosene¹⁰（煤油） in increasing quantities from 2020, it believes.

By this time new generation crop-based fuels should have been developed which do not compete with food crops.

Green groups have been critical of the destruction of rainforest to create the fuels and the resultant（合成的） loss of habitat for rare species.

They also say that with more farmland being turned over to grow profitable biofuels, food production has fallen and pushed up global prices, affecting supplies for the poorest people.