Fuelling controversy

Interest in biofuels for transport has increased markedly in recent years and so too have the concerns related to their production and use.  The competition increasingly set up between providing food or fuel is raising questions about the long-term contribution biofuels can make as fuels for vehicles.  Indeed, last month, the European Environment Agency (EEA) called for the EU to suspend its ten per cent target for biofuel use until more comprehensive scientific work has been done to assess their risks.  

The EEA report came one day after a World Bank report that suggests that biofuel production has contributed to an 83 per cent increase in global food prices in three years. However, factors such as increased food demand in China and India, weather and energy prices are all important.  Nevertheless, biofuels are increasingly considered as being an unhelpful additional stress in this respect.  Putting aside the competition with food supply, there are also important issues to be resolved concerning the environmental impact that biofuels have.

The recent report by the Select Committee on Environmental Audit raises serious questions regarding the use and environmental impact of biofuels for transport.  The Committee was most concerned by the use of ‘first generation’ biofuels; fuels derived from food and fodder crops.  By contrast, ‘second generation’ biofuels are produced from the whole of the plant, not just the sugar or oil-rich parts. Second generation fuels are currently not commercially viable but do have longer term-potential.  Their advantage over first generation fuels would be the avoidance of competition with food supply and reduced environmental impacts.  So what are these impacts and how important are they?

A shift away from petrol and diesel to alternative fuels such as biofuels requires different issues to be considered, which are also important for most other alternative fuels.  We have had over 100 years of environmental impacts that have been dominated by point of use emissions, whether related to local air pollution concerns or, in the more recent past, climate change.  The vast bulk of these impacts have been due to what comes out of the exhausts of vehicles.  A shift away from petrol and diesel will require impacts other than those at the point of use to be considered in much more detail.

There are other factors to be considered too: petrol and diesel are in many respects ideally suited for transport use due to their energy density — and this can be a problem for some competing alternative fuels.  Ethanol is not a bad alternative, but a car running on pure ethanol typically uses around 50 per cent more fuel per mile (by volume) compared with petrol.

One of the often-cited benefits of biofuels is that they are ‘carbon-neutral’.  The same carbon emitted during combustion is balanced by that in growing biomass to make the fuel in the first place.  However, to be fully carbon-neutral requires that all stages of the fuel cycle are also carbon neutral, meaning that harvesting, processing and transporting the fuels do not use fossil fuels.  Emissions of carbon are only part of the story though.

Assessing these impacts requires a different way of thinking that considers a much wider range of environmental impacts.  In the case of conventional fuels this is often called ‘well-to-wheel’ where emissions and their impacts are assessed from the extraction at the oil well through to the point of use.  In the case of biofuels a better description might be from ‘field to wheel’.  It is at the farm that emissions of pollutants other than carbon dioxide are potentially very important and can in some cases remove any carbon-neutrality benefit they have.  The petrol and diesel fuel cycle is generally dominated by discrete emissions that are usually well-characterised such as the emissions related to oil and gas extraction.  In the case of biofuels there are many more diffuse sources that can be difficult to measure and quantify.  Furthermore, these diffuse emissions include the release of other pollutants that are important to climate.

One of the key pollutants associated with farming is a greenhouse gas called nitrous oxide with a warming effect over 300 times that of carbon dioxide.  This means that even relatively small emissions of nitrous oxide can rapidly become important when considering the overall climate impacts of fuels.  

Rather than ‘carbon-nuetral’, a better description would be ‘climate-neutral’.  The extent to which nitrous oxide emissions are important depends on many factors including the type of biomass grown in the first place and the type and use of fertilizers employed.  These impacts are currently not very well characterised and more research is ongoing to help better quantify them.  What is essential, however, is that the full range of impacts is considered when comparing the relative merits of vehicular fuels.

Indeed, these issues are at the heart of the debate over biofuel impacts and studies vary widely in their assessment of their total climate impact. Under European conditions, bioethanol for example, is estimated to have a total greenhouse gas impact ranging from around 60 per cent less than petrol to no benefit at all.

One of the major advantages of biofuels over other alternative fuels is that they are in liquid form.  This allows them to fit into a  global infrastructure that has been developed and refined over decades to provide liquid fuels for transport at high levels of efficiency.  Furthermore, the global car industry has similarly honed its developments to use fuels that are in liquid form.  This gives biofuels the potential to reduce the climate impact of transport emissions quickly without the need for a completely new fuel infrastructure or vehicle technologies.  

Whilst there is unlikely to be a single solution, biofuels have the potential to make an important contribution — provided the full range of impacts is comprehensively quantified.  

Dr David Carslaw is a principal research fellow at the Institute for

Transport Studies at the University of Leeds.