Not all biofuels are created equal
Biofuels should be differentiated by more than just carbon intensity, with the type of crop, location and farming practices all playing a role in environmental impact
The publication of a special report on “Climate Change and Land” by the UN Intergovernmental Panel on Climate Change, and Greta Thunberg, the Swedish teenage climate activist, advocating for “natural climate solutions” are signs that land-based agriculture and extractive sectors are going to be in the spotlight as countries strengthen their climate policies in the years to come. As policymakers evaluate their policy options, the role of bioenergy is likely to be scrutinized.
The sustainability credentials of biofuel have always been disputed. Production of food crops as biofuel feedstock has been linked to deforestation and volatility in cereal prices. However, biofuel’s potential to reduce greenhouse gas emissions in the transport and energy sectors has made it an important part of climate policy in many countries. The use of biofuels in transport needs to increase from around 2% of the transportation mix to about 15% by 2050 to meet the 1.5 degrees Celsius warming target in the Paris Agreement, according to a 2017 report by the IPCC.
Recognizing this ambition, regulators have started to introduce rules to regulate the sustainability credentials of biofuel to ensure it becomes an effective climate policy tool. For example, carbon intensity scores are being used in California’s new fuel standards and there are restrictions on biofuel coming from high “land use change” risk sources in the EU’s Renewable Energy Directive.
Today, there are multiple methods to assess the environmental impact of biofuel, but carbon intensity is the metric adopted by most policymakers. However, the environmental impact of biofuels is not just about greenhouse gas emissions. In addition, the type of crop, place of origin and farming practices are all important factors that could enhance or tarnish the fuel’s sustainability credentials.
The importance of land
Carbon intensity, measured in grams of CO2 equivalent per megajoule of energy in the fuel, captures the greenhouse gas emissions from the production of the feedstock, the fuel conversion process and the combustion of the fuel.
In theory, biofuels are carbon-neutral at the point of use, meaning the amount of carbon emitted from their combustion would have been balanced by the carbon absorbed during the growth of the feedstock. The reality is a little more complicated. To begin with, conversion of feedstock into fuel requires energy, usually generated from fossil fuels.
Also, to achieve the balance, the speed at which the feedstock is regrown has to match the rate of biofuel consumption, which might not always be the case.
Despite that, the scientific consensus is that biofuels produced from feedstock grown on existing cropland are less carbon-intensive than fossil fuels such as diesel and petrol.
Biofuels made from conventional food crop feedstock such as corn, sugar cane or oilseeds generally have higher carbon intensity than their lignocellulosic counterparts made from switchgrass or straw. For instance, the carbon intensity of bioethanol produced from switchgrass is less than two-thirds that of fuel produced from corn. The extra carbon in corn-based biofuel comes from the greenhouse gas emitted during the manufacturing and application of nitrogen-based fertilizers, an essential ingredient in the industrial production of most food crops.
The picture is rosy until we take into account “land use change” – in other words, the clearing of native forests or grasslands. This is what critics of biofuels usually cite as the unintended consequence of biofuel production. The increased demand for biofuels would drive higher prices, and farmers would respond by converting forests to cropland to expand production.
Native ecosystems, such as tropical rainforests, are natural stores of carbon. They absorb carbon through the growth of trees and store them in the vegetation or soil. Clearing of these ecosystems would lead to the release of large amounts of carbon into the atmosphere, usually through burning and decomposition of vegetation.
This is the reason feedstock produced on land obtained from cleared forests has a significantly higher carbon intensity than feedstock grown on existing cropland. Biofuel derived from palm oil produced on land converted from forests is 80% more carbon intensive than conventional fuels. An EU study put the carbon intensity of biofuel produced from converted peatland in Indonesia and Malaysia, one of the most carbon-dense ecosystems in the world, 231 gCO2e/ MJ, almost two-and-a-half times higher than that of the average of gasoline and diesel.
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