A paper published in Nature Climate Change suggests that planting trees for use as a biofuel source, near populated areas, is likely to increase human deaths due to inhalation of ozone. Increased levels of isoprene emitted from such trees, when interacting with other air pollutants can lead to increased levels of ozone in the air which might also lead to lower crop yields.
In Europe, fast growing trees such as eucalyptus, willow and poplar, have been planted and are being used to create biofuels which can be burned in engines and generators. Such trees have been seen as an attractive alternative to other edible crops, such as corn, because growing them does not conflict with food production goals. However these types of trees emit high levels of the chemical isoprene into the air. Prior research has shown that when isoprene mixes with other pollutants (such as nitric oxides), ozone is produced. In this new research, the team suggests that planting enough trees to meet the EU’s 2020 biofuel target could result in up to 1,400 deaths per year in Europe, along with $7.1 billion in additional health care costs and crop losses - on top of the 22,000 deaths already attributable to ozone pollution in Europe each year.
Plans for using trees as a biofuel resource generally involve planting near large urban areas to avoid incurring transportation costs. Such plantings, the researchers suggest, would lead to lung problems and deaths for people living in those areas. Conversely, if large numbers of such trees were planted in rural areas, edible crops would be adversely impacted, leading to less production and higher costs. The team also notes that ozone is currently blamed (by the European Environment Agency).
Ground-level ozone is a priority air pollutant, causing ~ 22,000 excess deaths per year in Europe, significant reductions in crop yields and loss of biodiversity. 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 (~ 90% of total VOC emissions) released from vegetation globally. Isoprene (2-methyl-1,3-butadiene) is the most significant biogenic VOC in terms of mass (around 500 TgC yr−1) and chemical reactivity and plays an important role in the mediation of ground-level ozone concentrations. 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.
Ashworth K, Wild O, Hewitt C N (2013). Impacts of biofuel cultivation on mortality and crop yields, Nature Climate Change doi:10.1038/nclimate 1788
You can access the paper (subscription only) here.
There are also helpful summaries of the research findings to be found here and here.
25 Feb 2013
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