Biofuels will only cut transport emissions if crops are selected carefully and changes to land minimized according to “Biofuels and synthetic fuels in the US and China: A review of Well-to-Wheel energy use and greenhouse gas emissions with the impact of land-use change.”
The review, by University of Oxford Smith School of Enterprise and Environment scientists, has found that corn-based ethanol, the most widely used biofuel, often increases emissions compared to fossil fuels largely because of land-use changes.
Ethanol produced from sugarcane, or the woody shrub cassava, and biodiesel from soybean, rapeseed or jatropha – a small tree - can cut emissions but by very little if carbon-storing forests and grasslands are cleared to grow these crops.
Only one fuel source known as cellulosic biomass – urban waste or the leftovers from crops - has significant potential for cutting transport emissions, because it has minimal land-use impacts.
The scientists warn: “Converting grasslands in the US to corn fields for bioethanol production could cause [a] huge carbon debt through direct land-use change. Diverting US corn export to bioethanol production could potentially cause [an] even greater carbon debt through indirect land-use change.”
The authors of the study, Dr Xiaoyu Yan, Dr Oliver Inderwildi and Professor Sir David King, the Smith School’s Director, focused on biofuel production in the US and China where its use is set to rise rapidly because of fears over energy security.
They found that comparisons of CO2 emissions from different fuels were only valid if the effects of land-use changes were taken into account.
The availability of land and water will limit corn ethanol production in the US, where it is heavily subsidized. China, however, and European countries, is increasingly making biofuel from non-food sources. These sources could provide a significant amount of China’s road fuel by 2030, the scientists say.
Ethanol made from leftovers uses significantly less fossil fuel during production, cuts emissions and does not require changes to land. This is significant in China, where energy use is soaring because of the country’s rapid development.
Dr Yan said: “It is extremely unlikely that a major share of the current demand for transport fuel demand can be provided by biofuels. Biofuels will only cut transport emissions if appropriate feedstocks are used and emissions from land-use change are minimized.”
Dr Inderwildi said: “Sustainably manufactured biofuels can reduce emissions in the short term but unless there’s a significant breakthrough in fuel production from algae, the only source with long-term potential, problems linked with land use change will limit the impact of biofuels.
Sir David King said: “While useful to an extent, sustainably produced biofuels are far from the only solution to cutting transport emissions. They must be part of a range of technological innovations and transport measures including electric cars, congestion charging and higher taxes for gas-guzzling cars.”
* Biofuels and synthetic fuels in the US and China: A review of Well-to-Wheel energy use and greenhouse gas emissions with the impact of land-use change, Yan X, Inderwildi OR, King DA, Energy and Environmental Science, the journal of the Royal Society of Chemistry.
* Direct land-use change is the clearance of forests or grasslands for crops; indirect change occurs when a crop is used for fuel instead of food, forcing the farmer to clear new land for food crops.
* Transport consumes 60% of global oil production, of which 80% is for road transport.
* Ethanol and biodiesel are the most-used biofuels.
* If ethanol production targets set by the US, Asia and Europe are met, production could total 125 billion litres by 2020 compared to 46bn litres – or 4% of petrol demand - in 2007 (Balat M, Balat H, Applied Energy 2009, 86, 2273).
* Ethanol can also be made from sorghum grain and its production is being trialed in China. But its production uses more fuel, and has higher emissions, than petrol. Cassava-based ethanol could cut emissions by 25% however and is readily grown on mountainous or poor quality farmland.
* Around 10bn litres of biodiesel was produced in 2007 with the potential for much more. Biodiesel is made from edible oil crops such as rapeseed in the EU, soybean in the US and South America, and palm oil in south-east Asia.
· First generation biofuels – those made from food crops – only cut emissions if land use changes are ignored. Many have significantly higher emissions than oil-based fuels when land use impacts are included. These emission debts can take decades or centuries to repay. Additional effects include soil erosion, increased use of chemicals including fertilizer (and with it more emissions) and biodiversity loss. In other words, retaining and restoring forests can combat climate change more effectively than first generation biofuel production.
