Plant-based fuels could increase emissions

Biofuels’ contribution to global warming is a contentious issue for environmentalists.

Plant-based fuels can reduce transport emissions of carbon dioxide (CO2), the most common gas linked with climate change. But looking at the bigger picture biofuels may not have such a positive impact on greenhouse gas emissions.

The first and often biggest greenhouse gas problem comes right at the start. Farming crops to turn into biofuels means using a lot of fertilizer, says Ariel Brunner of conservation group Birdlife International and fertilizer emits a lot of nitrous oxide which is a greenhouse gas more than 300 times as potent as CO2.

In the worst case scenario, says Brunner, intensive agriculture can lead to so much fertilizer being used that greenhouse gas emissions over the whole lifecycle of a biofuel can cancel out all the CO2 reductions. In this case, he says, biofuels are "worse than oil".

Even if biofuel crops are farmed in a more environmentally friendly way, turning them into fuel can pump up the CO2 emissions.

"A big chunk of the lifecycle emissions come at this industrial phase," explains Brunner. "The biggest problem comes if coal is used to run the biofuel production plant, as is sometimes the case in Germany. Natural gas, as used in the US, is not quite as bad but still quite awful."

The best option, he suggests, is to use renewable energy for biofuel production factories. With renewables still struggling to increase their share of the EU energy mix, the renewable biofuel plant remains a rare site.

Many of the crops used to produce European biofuels are grown outside the EU. And shipping them, or the fuel they produce, to Europe, uses energy.

Then there is the problem of what the energy crop might have displaced, which can be a particular issue outside the EU.

"If you cut down a tropical rainforest," says Brunner, "you’re left with these tonnes and tonnes of carbon [the trees] to dispose of." These trees are usually disposed of by burning. "These initial emissions will be so big that your first years of producing biofuels will just be offsetting that start," he points out.

Getting energy from renewable plants might appear to be a good way of avoiding CO2-emitting hydrocarbons, but the benefits are qualified.

Biofuels’ contribution to global warming is a contentious issue for environmentalists.