Biogenic emissions in the face of climate change

Biogenic emissions, such as isoprene and monoterpenes, are important contributors to the air quality of the troposphere. In combination with anthropogenic NOx compounds, biogenic VOCs can contribute to increased regional ozone levels. Biogenic emissions are driven primarily by temperature and solar radiation, thus it is expected that they will be sensitive to changes in climate. And biogenic emission inventories are an important first step for any air quality model. There are many facets to climate change that may impact biogenic emissions, such as the increased global temperatures, changes in radiation that reaches the surface, increased CO₂ concentrations altering biomass and plant productivity, changes in land use management and/or altering species distribution and composition, to name a few. However, with any future modeling work, there is also inherent variation in climate parameters due to natural cycles. The goal of this work is to assess if the change in climate parameters (primarily temperature and radiation) between historical and future periods is significant enough to alter biogenic emissions beyond the natural variation of emissions as a function of climate. In other words, do the estimated variations with future climate scenarios exceed the natural variation of current climate cycles? And if they do, how does that affect biogenic emissions?

To evaluate the variations in climate and emissions, a combination of measurements and modeling results will be invoked. A long-term (4 –year) data record of eddy covariance isoprene flux measurements has been collected above a hardwood forest in northern lower MI. With this record of isoprene fluxes, inter-annual variations in biogenic emissions can be determined along with associated variations in the natural climate parameters. In addition, future climate variations will be estimated using output from a general circulation model (GCM) simulation for current and future decadal periods. Based on these decadal climate data sets, the interannual variations in biogenic emission drivers will be compared to the long-term flux record, and the impacts of these variations on isoprene emissions will be determined. The results will be used to assess whether predicted climate changes are significant in terms of isoprene emissions compared to observed interannual variability in isoprene emissions.