Historic 1971-2000 modal Vegetation Type, MC2

The dynamic vegetation model MC2 used a suite of climate futures from the Coupled Model Intercomparison Project (CMIP5, http://cmip-pcmdi.llnl.gov/cmip5/  downscaled using a fairly new statistical downscaling approach (Abatzoglou 2011), Multivariate Adaptive Constructed Analogs (MACA), over the western US. The vegetation model was run on the NASA Earth Exchange (NEX) platform at 4km resolution for 2 representative concentration pathways (RCPs) 8.5 and 4.5 (Moss et al. 2010, van Vuuren et. al 2011). Representative Concentration Pathway define a specific emissions trajectory and subsequent radiative forcing. Radiative forcing is a measure of the influence a factor has in altering the balance of incoming and outgoing energy in the Earth-atmosphere system, measured in Watts per square meter. For energy and industry CO2 emissions, RCP8.5 represents the 90th percentile of the reference emissions range rising the radiative forcing to 8.5 W/m2 in 2100. RCP 4.5 is a stabilization scenario and assumes that climate policies, in this instance the introduction of a set of global greenhouse gas emissions prices, are invoked to achieve the goal of limiting emissions, concentrations and radiative forcing. RCP 4.5 stabilizes radiative forcing at 4.5 Watts per meter squared (Wm-2, approximately 650 ppm CO2-equivalent) in the year 2100 without ever exceeding that value.