Growing demands for food and biofuels have led to the conversion of grasslands and forests to agricultural land. The associated changes in plant type affect the magnitude of isoprene emissions from vegetation, and lead to enhanced levels of surface ozone at a local level, numerical simulations suggest.
Catherine Hardacre, of the University of Edinburgh, and colleagues constrain the effect of projected changes in land use on plant isoprene emissions in the first half of the twenty-first century, using a broad range of land-use scenarios and a biogenic volatile organic compound emissions model. They find that the cultivation of biofuel crops — which emit large quantities of isoprene — in the Northern Hemisphere leads to a rise in emissions. In contrast, the replacement of isoprene-emitting forest and grasslands with food crops, particularly in Brazil and sub-Saharan Africa, reduces emissions. By 2030, the global isoprene load could increase by up to 1.4%, or decline by up to 1.7%, depending on the balance of these changes.
Chemistry transport modelling suggests that at the global scale, the projected changes in isoprene emissions have only a minimal effect on levels of the surface pollutant ozone, a product of isoprene oxidation. However, significant increases in surface ozone concentrations are evident at a local level, particularly in North America, China and boreal Asia.