The current obsession with ‘carbon neutral’ – in many ways a very good one – has meant that people are very keen to label things carbon neutral when in fact they are nothing of the sort. Biofuels is a prime example. If you look at it simply – you burn a tree and release carbon but, through photosynthesis, it took in that much carbon while it was growing. However, a whole lifecycle analysis is needed to understand how sustainable these crops are. This takes into account emissions from transportation, inputs such as fertiliser, and the disposal of waste products.
Cambridge scientists did this analysis for the production of bioethanol from willow in the UK. Their results showed that bioethanol from willow would produce over 80% less greenhouse gas than burning gasoline from fossil fuels. These savings are much greater than the ‘first-generation biofuels’ that have been grown in the US and come from crops such as corn. They make ethanol from willow seem like an appealing option.
A major advantage of willow over first-generation biofuels is that it can be grown on marginal land. It even improves the soil quality; willows are coppiced so only replanted every 30 years. The soil isn’t ploughed in this time so any carbon that the tree sequesters in the soil remains there.
However, it’s not yet economically viable. A high capital investment is needed, and the provision of the willows themselves and enzymes needed to make the ethanol are expensive. The study suggests that selective breeding can help change this. The significant genetic diversity of willows can be exploited through breeding to make them even more suitable for biofuels use. For example, a higher ratio of cellulose to lignin would increase the yield of ethanol.
A.L. Stephenson, P. Dupree, S.A. Scott and J.S. Dennis (2010) The environmental and economic sustainability of potential bioethanol from willow in the UK. Bioresource Technology 101, 9612-9623
I think this research again highlights the point that has come up in our discussion of GM crops – just because some of the earlier biofuels ideas using food crops turned out to be a bad idea, it doesn’t mean that there’s no potential for biofuels to reduce greenhouse gas emissions.