60 second guide to… Biofuels

Are biofuels an effective way of reducing greenhouse gas emissions, or more trouble than they're worth?

What are biofuels?

Biofuels are the plant-based alternatives to oil-based fuels such as petrol, diesel and heating oil. Burning biodiesel emits CO2, but this is offset by the fact that the crop used to produce it uses CO2 from the atmosphere to grow.

However, the environmental benefits of biofuels are hotly disputed, with some green commentators claiming that they cause more harm than good.

There are two main kinds of bio-fuel: biodiesel and ethanol.

Biodiesel

As the name suggests, biodiesel is designed for use in diesel engines. It is very similar to vegetable oil and is produced from the same kinds of plants – oil-rich sources such as sunflower, palm, rapeseed and groundnut. It can also be made from animal fats or oils recycled from restaurants.

Biodiesel can be used neat in some diesel cars. But at present it's more commonly found in a mix with regular diesel – typically 5 per cent biodiesel with diesel fuel. This mix can be used in any diesel car.

Ethanol

Ethanol-based biofuels are designed for use in petrol engines. It is produced mainly from sugar and maize but it can also be made from many other cereal crops, such as wheat and barley. Ethanol is particularly popular in Brazil, where around 30 per cent of vehicle fuel is produced from sugar cane.

Like biodiesel, ethanol is typically added to conventional petrol, which allows it to be used in any car. However, some special cars, such as the flexible fuel vehicles common in Brazil, can handle ethanol in much higher concentrations.

Driving destruction

Growing fuel in fields is an attractive idea but serious concerns have been raised over the side-effects of the burgeoning market for biofuels.

The main worry is that the rush for biofuels will impact on our ability to grow sufficient food crops, which would be disastrous for poor urban populations. The other concern is that it will boost the incentive for people in tropical countries to clear rainforests and grow crops – disastrous for the environment.

But production of biofuels is still rising and the EU wants them to account for 10 per cent of fuel for transport by 2020.

Hidden emissions

Another argument against biofuels is that they may not be as climate-friendly as they appear. It's true that burning a biofuel releases CO2 equal to or less than that soaked up by the plants as they grew.

But that doesn't take into account the greenhouse emissions caused by growing the plants in the first place. For example, CO2 from fertiliser factories and tractors, and nitrous oxides released by ploughing the soil.

Blessing or curse?

The total environmental impact of a biofuel is difficult to measure. It depends on the crop, the farming practices and even the degree to which rainforests are protected in tropical countries.

While biofuels continue to be promoted by some policymakers, on both sides of the Atlantic, many experts remain highly sceptical of their benefits. In January, the UK’s government’s Environment Audit Committee recommended dropping biofuel targets. Author and journalist George Monbiot has even gone so far as to describe biofuels as an "agricultural crime against humanity".

Future fuels

As for the future, cellulosic biofuels, made from low-input crops that can be grown on marginal lands, could bring clearer benefits. But it remains to be seen how long it will be before these next-generation fuels become practical and economical.

A more promising solution may be algae, say some experts. Algae doubles their size in a day, making them among the most efficient organisims at capturing light energy and converting it into biomass. And unlike biofuels such as corn, algae don’t use up land or water that could be used to grow food crops.

Some experts believe that algae on around 20 million aces of land would be enough to supply all of the US’s transportation fuel needs, which is a small fraction of its agricultural land. Algae need a good supply of carbon dioxide to grow at an acceptable rate, and they can feed on nutrients in sewage. Both of these resources are readily available so biodiesel from algae could offer real hope.

As a result, algae are getting increased attention from oil companies. Shell, which is building a pilot facility in Hawaii to grow and test marine algae for its potential on an industrial scale.