Now, a study by researchers at EMPA in Switzerland has carried out environmental life-cycle assessments of biofuels for transport – incorporating factors such as fertilizer use – rainforest clearance, biodiversity loss and soil acidification, as well as the fuel’s greenhouse gas emissions. The Swiss government commissioned the report, which concluded that not all biofuels can reduce environmental impacts compared to those from fossil fuels.

"It is true that reductions in greenhouse gas emissions of more than 30% can be obtained with many biofuels," say Rainer Zah and colleagues at EMPA in the report's conclusion. "However, most of the production paths display higher impacts than petrol in various other environmental indicators."

These indicators can include destruction of native ecosystems, pollution, soil erosion, emission of harmful trace gases such as nitrous oxide, hydrological functioning and damage to human health.

The team used two different life-cycle assessment techniques to look at bioethanol, biodiesel, methanol and methane made by various routes, as well as diesel, petrol and natural gas. Biofuels made from waste products – such as biodiesel made from waste cooking oil or methane made from liquid manure – generally had the lowest environmental impact.

Of the 26 biofuels examined, 13 reduced greenhouse gas emissions by more than 50%. These included biofuels made from liquid manure, biodiesel made from waste cooking oil, methanol and methane from wood, and bioethanol from domestic biomass (grass, wood, sugar beets or whey), Brazilian sugar cane and Chinese sorghum. At worst, the emissions from Brazilian soy biodiesel were slightly higher than those from petrol.

The EMPA researchers found that most of the environmental impact associated with the biofuels came from the agricultural cultivation of the raw materials used to produce them. This cultivation could involve machine use, fertilizer manufacture, pesticide application and rainforest clearance as well as potentially causing direct emissions such as nitrous oxide. For cultivation in tropical areas, the key problems were the clear-cutting and burning of rainforests, which release large quantities of carbon dioxide, increase air pollution and harm biodiversity. For growth of biofuel crops in mid-latitudes, intensive fertilizer use, mechanical tilling of the soil and lower yields were the primary issues.

The production of the fuel itself generally created a much lower impact than cultivation, as did transport to Switzerland. Provided that the long-distance routes were covered in tank ships or in pipelines, this typically contributed much less than 10% of overall greenhouse gas emissions and played "only a secondary role" from an environmental standpoint.

"Of all the production paths tested, at present it is primarily the utilization of biogenic waste material and wood and the utilization of grass for ethanol production that bring a reduction in environmental impact – versus the fossil reference," the researchers concluded. "Nonetheless, the environmental impact of biofuels – unlike that of fossil fuels – can be reduced a lot by appropriate measures."

The scientists say that in future it will be possible to achieve better results for a number of production paths. They believe that innovative processes such as biomass-to-liquid will also become more important, although they were not able to include them in the study. The report excluded second-generation biofuels like those made from the breakdown of plant cellulose or lignin, because of insufficient data.

Wider issues

According to an analysis of the EMPA report in Science, it shows that the economically most important biofuels, namely US corn ethanol, Brazilian sugarcane ethanol and soy diesel, and Malaysian palm-oil diesel, have greater aggregate environmental costs than do fossil fuels.

Jörn Scharlemann and William Laurance of the Smithsonian Tropical Research Institute, Panama, raise concerns that the analysis doesn’t look at indirect effects, for example the trend for American farmers to shift from growing soy to growing corn encouraged by US government subsidies designed to boost corn-based ethanol production. This move is helping to drive up global soy prices, increasing incentives to destroy Amazonian forests and Brazilian tropical savannas for soy production, according to the pair.

"Governments should be far more selective about which biofuel crops they support through subsidies and tax benefits," say Scharlemann and Laurance in Science. "For example, multibillion-dollar subsidies for US grain production appear to be a perverse incentive from a rational cost-benefit perspective."

Last year, the international aid agency Oxfam raised concerns about EU plans to make it mandatory by 2020 for 10% of all member states' transport fuels to come from biofuels. Oxfam believes that the resulting demand for biofuel imports could threaten to force poor people from their land, destroy their livelihoods, lead to the exploitation of workers and hurt the availability and affordability of food.

It’s a complex issue – let’s hope that research into next-generation biofuels can iron out many, if not all, of these problems.