Modelling changes in VOC emission in response to climate change in the continental United States

The alteration of climate is driven not only by anthropogenic activities, b ut also by biosphere processes that change in conjunction with climate. Emi ssion of volatile organic compounds (VOCs) from vegetation may be particula rly sensitive to changes in climate and may play an important role in clima te forcing through their influence on the atmospheric oxidative balance, gr eenhouse gas concentration, and the formation of aerosols. Using the VEMAP vegetation database and associated vegetation responses to climate change, this study examined the independent and combined effects of simulated chang es in temperature, CO2 concentration, and vegetation distribution on annual emissions of isoprene, monoterpenes, and other reactive VOCs (ORVOCs) from potential vegetation of the continental United States. Temperature effects were modelled according to the direct influence of temperature on enzymati c isoprene production and the vapour pressure of monoterpenes and ORVOCs. T he effect of elevated CO2 concentration was modelled according to increases in foliar biomass per unit of emitting surface area. The effects of vegeta tion distribution reflects simulated changes in species spatial distributio n and areal coverage by 21 different vegetation classes. Simulated climate warming associated with a doubled atmospheric CO2 concentration enhanced to tal modelled VOC emission by 81.8% (isoprene + 82.1%, monoterpenes + 81.6%, ORVOC + 81.1%), whereas a simulated doubled CO2 alone enhanced total model led VOC emission by only + 11.8% (isoprene + 13.7%, monoterpenes + 4.1%, OR VOC + 11.7%). A simulated redistribution of vegetation in response to alter ed temperatures and precipitation patterns caused total modelled VOC emissi on to decline by 10.4% (isoprene -11.7%, monoterpenes -18.6%, ORVOC 0.0%) d riven by a decline in area covered by vegetation classes emitting VOCs at h igh rates. Thus, the positive effect of leaf-level adjustments to elevated CO2 (i.e. increases in foliar biomass) is balanced by the negative effect o f ecosystem-level adjustments to climate (i.e. decreases in areal coverage of species emitting VOC at high rates).