Biofuels, made from plant material, are often called ”green” or “environmentally friendly” compared to conventional transport fuels such as gasoline and diesel.

Are they?

The idea is that biofuels merely exploit a carbon cycle - plants store carbon dioxide, the main greenhouse gas, as they grow and release it after they die. So biofuels can slow global warming by cutting use of fossil fuels that release greenhouse gases trapped for millions of years. Biofuels can also help countries bolster their energy security and shore up dwindling farm incomes.

But some of them have nasty side effects and arouse strong views.

One problem is that biofuels narrow the range of habitats for wildlife. Some tropical forests — huge stores of carbon — are cleared to grow crops such as palm oil in Malaysia and Indonesia. Environmentalists say that wildlife such as the orang utan is coming under threat from palm oil plantations in Indonesia.

Other biofuels, such as ethanol produced by Brazil from sugar cane, get better ratings. Unlike palm oil, sugar cane doesn’t grow in climates where it could compete with tropical rainforests. But planned increases in Brazilian soybean production could encroach on the Amazon.

In Europe and North America, biofuels are mainly derived from intensively farmed food crops such as corn (maize), rapeseed and wheat. One report, disputed by biofuels producers, said that using fertilisers to grow these crops produces more greenhouse gases than burning conventional diesel and gasoline.

The drive for biofuels, taking farm land away from crops, is one factor stoking rising food prices. Maize prices have been surging despite bumper crops in the United States, Brazil and Mexico.

So are biofuels helping to protect the environment and do they merit the ”green” tag?

If not, how should we describe them — maybe ”renewable” or ”alternative”?

Please tell us what you think.

Biofuels, made from plant material, are often called "green" or "environmentally friendly" compared to conventional transport fuels such as gasoline and diesel.

Are they?

The idea is that biofuels merely exploit a carbon cycle - plants store carbon dioxide, the main greenhouse gas, as they grow and release it after they die. So biofuels can slow global warming by cutting use of fossil fuels that release greenhouse gases trapped for millions of years. Biofuels can also help countries bolster their energy security and shore up dwindling farm incomes.

But some of them have nasty side effects and arouse strong views.

One problem is that biofuels narrow the range of habitats for wildlife. Some tropical forests -- huge stores of carbon -- are cleared to grow crops such as palm oil in Malaysia and Indonesia. Environmentalists say that wildlife such as the orang utan is coming under threat from palm oil plantations in Indonesia.

Other biofuels, such as ethanol produced by Brazil from sugar cane, get better ratings. Unlike palm oil, sugar cane doesn't grow in climates where it could compete with tropical rainforests. But planned increases in Brazilian soybean production could encroach on the Amazon.

In Europe and North America, biofuels are mainly derived from intensively farmed food crops such as corn (maize), rapeseed and wheat. One report, disputed by biofuels producers, said that using fertilisers to grow these crops produces more greenhouse gases than burning conventional diesel and gasoline.

The drive for biofuels, taking farm land away from crops, is one factor stoking rising food prices. Maize prices have been surging despite bumper crops in the United States, Brazil and Mexico.

So are biofuels helping to protect the environment and do they merit the "green" tag?

If not, how should we describe them -- maybe "renewable" or "alternative"?

Please tell us what you think.