Título original: Podem os biocombustíveis ajudar a combater o aquecimento global, ou farão o problema ainda pior?

Why are we asking this question now?
The European Union is having second thoughts about its policy aimed at stimulating the production of biofuel – transport fuel derived from crops and other vegetation or organic waste. Stavros Dimas, the EU environment commissioner, admitted yesterday that the EU did not foresee the scale of the problems raised by Europe's target of deriving 10 per cent of its transport fuel from plant material. The rush to produce biofuels is reported to have increased the cost of food on the global market, destroyed tracts of rainforest in tropical countries and to have had little overall impact on reducing greenhouse gases.

"We have seen that the environmental problems caused by biofuels and also the social problems are bigger than we thought they were. So we have to move very carefully," Mr Dimas told the BBC. Yesterday also saw the publication of a report on biofuel by the Royal Society in London which had asked a committee of experts to examine the complex issues surrounding the technology. The report concluded that there is no simple answer to whether biofuels are good or bad for the environment, and that each type of biofuel – and how it is produced – has to be considered on its own merits.

What are biofuels and how are they meant to help fight global warming?
The principle behind biofuels is essentially the same as that behind fossil fuels such as oil. Both biofuels and fossil fuels have stored the energy of the Sun in the form of biologically-produced chemicals called hydrocarbons. The energy stored in the fuels results from the ability of plants to carry out photosynthesis – the manufacture of sugar, starch and other complex organic molecules using sunlight.

However, unlike fossil fuels, biofuels have the potential to be carbon neutral, meaning that the loss of carbon dioxide to the atmosphere caused by burning them is offset by the absorption of carbon dioxide by the biofuel plants when they are growing. (The carbon locked up in fossil fuels was put there by plants that lived and photosynthesised millions of years ago.)

If this were true – that there is a perfect balance between absorption and production of carbon dioxide – then burning biofuels would not cause an overall increase in levels of atmospheric carbon dioxide, one of the principal greenhouse gases. Unlike fossil fuels, biofuels therefore have the potential to help to prevent global warming if they could replace the burning of oil-based fuels such as gasoline and diesel. They also have the added advantage over fossil fuels in that they are renewable.

It sounds like the perfect answer to all our worries
Yes it sounds like it, but the truth is not so straightforward. There are many problems with biofuel production that can significantly change the carbon balance sheet.

For a start, biofuel crops often need fertilisers and pesticides which are made from oil. The machinery used to grow, transport and process the crop is also often powered by fossil fuel. Then there are the tracts of pristine forests that are cut down to grow biofuel crops. This results in the loss of natural "carbon sinks" that are invaluable in the fight against climate change. In short, biofuels are not the universal panacea that some people believe them to be.

What can we use biofuels for?
Biofuels are mainly used for transport. This is important in the fight against climate change because, worldwide, transport accounts for something like 20 per cent of carbon dioxide emissions.

Carbon dioxide emissions from transport are also experiencing the highest growth of any energy-intensive sector. By 2030, it is predicted that carbon emissions from transport will be 80 per cent higher than current levels. So biofuels are seen as a critical element in the fight to offset these expected increases.

Biofuels can come in one of three varieties. The first is bioethanol, or alcohol, which is usually produced by the fermentation of sugars. The second is biodiesel produced from processing plant oils and the third is synthetic biofuels, which result in fuels identical to petrol, diesel and even aviation fuel.

What has gone wrong with the biofuel dream?
People have failed to look at the overall costs and benefits from the complete production process, from "farm to forecourt". This is sometimes known as life-cycle assessment and it involves taking into account all aspects of the carbon budget from one end of the production process to the other. When this is done, the simple assumptions that politicians and some environmentalists have made about the benefits begin to look hopelessly optimistic.

Take for example biofuels made from maize (in the US way) and from sugar (in the Brazilian way). The Worldwatch Institute estimates that the reductions in greenhouse gases on a life-cycle assessment resulting from ethanol produced in Brazil is about 80 per cent, compared with just 10 per cent from ethanol made from intensively-farmed maize in the US.

But the problem is not just about the efficiency of biofuel production. Britain will never be self-sufficient in biofuel and so other parts of the world will be expected to set aside land and water to supplement our needs. This has led to a growth in non-food crops in parts of the world where millions already go hungry. It has also put pressure on wildlife as forests are cut down to clear land for biofuel crops.

What can be done to retrieve the situation?
The Royal Society believes that current policy frameworks on biofuels in the EU and elsewhere must be changed so they encourage an overall reduction of greenhouse gases rather than being aimed simply at reducing reliance on imported oil. "As a result, there is no incentive to invest in the systems that would deliver low GHG [greenhouse gas] biofuels," says its report. Britain should, it says, set its own targets on reducing greenhouse gas emissions with biofuels – something that is not currently done with the Government's Renewable Transport Fuel Obligation, which comes into force this April.

So are biofuels good or bad for the environment?
The right sort of biofuel crops, grown in the right way and in the right place can be better for the environment in the longer term than burning fossil fuels. However, there are many things that can be overlooked and, in order to answer the question, people need to assess the entire life cycle of the production process, including its impact on local people and wildlife.

Is it right to set targets for biofuel use?
Yes...
* Without targets, there is nothing to aim for in terms of making biofuels compete with fossil fuels
* It would be impossible to quantify improvements in biofuel production without targets
* Targets stimulate ways of making biofuel even better for the environment

No...
* Targets emphasise short-term benefits at the expense of long-term gains
* Existing targets are aimed at reducing reliance on imported oil rather than lowering greenhouse gases
* There is no benefit in setting targets that are not met, or are not met everywhere in the world

(By Steve Connor, The Independent, 15/01/2008)