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Biofuels were first pioneered in the early days of car manufacturing. Cheap fossil fuels soon overtook them as our fuel of choice, but concerns about climate change have revived interest in them - global biofuel production doubled between 2000 and 2007, and is expected to double again by 2011.
'First generation' biofuels, mainly produced from food crops, were initially regarded as a potential renewable and sustainable source of energy. But hopes faded as researchers found biofuels offer small or even negative greenhouse gas emission savings across their life cycle compared with fossil fuels.
Problems associated with environmental impact have also arisen. In Indonesia, for example, large areas of rainforest have been cleared to plant palm oils for biofuels. The country's total rainforest area will soon be about half of what it was in 1990 if current trends continue.
There have been social and economic effects too.
On the plus side, biofuel production has helped some farmers and workers boost their incomes and develop their businesses. But, as with many other types of agriculture, other workers and farmers have experienced inadequate working conditions and negative health effects from pesticide use, for example.
In Colombia, local communities have reportedly lost control of - or even been evicted from - their land to make way for biofuel production.
There is also an ongoing debate among campaigners and scientists about whether biofuel production diverts land and water away from food production, potentially limiting local food supplies and driving up prices.
A new generation of biofuels
Scientists are developing a new generation of biofuels to help avoid such problems. For example, research is exploring the use of plants' inedible, woody parts for biofuel production that would allow non-food crops such as bushes, trees and agricultural waste to be used. Trials are also underway in the United States on using algae to produce biodiesel.
Genetic modification is being used to introduce favourable traits into biofuel crops, such as higher yields or the ability to grow on non-arable land. For example, scientists are developing a genetically-modified poplar tree that is a more accessible source of cellulose for bioethanol production.
And the emerging field of synthetic biology is aiming to develop entirely new means of generating biofuels, for example by building microbes that produce hydrocarbons.