Impacts of biofuel cultivation on mortality and crop yields

Ground-level ozone is a priority air pollutant, causing similar to 22,000 excess deaths per year in Europe(1), significant reductions in crop yields(2) and loss of biodiversity(3). It is produced in the troposphere through photochemical reactions involving oxides of nitrogen (NOx) and volatile organic compounds (VOCs). The biosphere is the main source of VOCs, with an estimated 1,150 TgC yr(-1) (similar to 90% of total VOC emissions) released from vegetation globally(4). Isoprene (2-methyl-1,3-butadiene) is the most significant biogenic VOC in terms of mass (around 500 TgC yr(-1)) and chemical reactivity(4) and plays an important role in the mediation of ground-level ozone concentrations(5). Concerns about climate change and energy security are driving an aggressive expansion of bioenergy crop production and many of these plant species emit more isoprene than the traditional crops they are replacing. Here we quantify the increases in isoprene emission rates caused by cultivation of 72 Mha of biofuel crops in Europe. We then estimate the resultant changes in ground-level ozone concentrations and the impacts on human mortality and crop yields that these could cause. Our study highlights the need to consider more than simple carbon budgets when considering the cultivation of biofuel feedstock crops for greenhouse-gas mitigation.