Probabilistic estimation of future emissions of isoprene and surface oxidant chemistry associated with land-use change in response to growing food needs
We quantify the impact of land-use change, de-termined by our growing demand for food and biofuel pro-duction, on isoprene emissions and subsequent atmospheric oxidant chemistry in 2015 and 2030, relative to 1990, ignor-ing compound climate change effects over that period. We estimate isoprene emissions from an ensemble (n = 1000) of land-use change realizations from 1990–2050, broadly guided by the IPCC AR4/SRES scenarios A1 and B1. We also superimpose land-use change required to address pro-jected biofuel usage using two scenarios: (1) assuming that world governments make no changes to biofuel policy after 2009, and (2) assuming that world governments develop bio-fuel policy with the aim of keeping equivalent atmospheric CO 2 at 450 ppm. We present the median and interquartile range (IQR) statistics of the ensemble and show that land-use change between −1.50 × 10 12 m 2 to +6.06 × 10 12 m 2 was found to drive changes in the global isoprene burden of −3.5 to +2.8 Tg yr −1 in 2015 and −7.7 to +6.4 Tg yr −1 in 2030. We use land-use change realizations correspond-ing to the median and IQR of these emission estimates to drive the GEOS-Chem global 3-D chemistry transport model to investigate the perturbation to global and regional surface concentrations of isoprene, nitrogen oxides (NO+NO 2), and the atmospheric concentration and deposition of ozone (O 3). We show that across subcontinental regions the monthly sur-face O 3 increases by 0.1–0.8 ppb, relative to a zero land-use change calculation, driven by increases (decreases) in surface isoprene in high (low) NO x environments. At the local scale (4 • × 5 •) we find that surface O 3 increases by 5–12 ppb over temperate North America, China and boreal Eurasia, driven by large increases in isoprene emissions from short-rotation coppice crop cultivation for biofuel production.