Two future climate change scenarios at a resolution of 0.5 degree latitude/longitude for the conterminous United States were used in the Vegetation Ecosystems Modelling Analysis Project (VEMAP): a moderately warm scenario produced by the general circulation model from the Hadley Climate Centre [Johns et al., 1997; Mitchell and Johns, 1997], HADCM2SUL (up to a 2.8oC increase in average annual U.S. temperature in 2100) and a warmer scenario (up to a 5.8oC increase in average annual U.S. temperature in 2100), CGCM1, from the Canadian Climate Center [Boer et al., 1999a, 1999b; Flato et al., 1999]. Both general circulation models (GCMs) included sulfate aerosols and a fully dynamic 3-D ocean. Both transient scenarios started in 1895 and ran to the present using observed CO2 increases [Schimel et al., 2000]. They used IPCC projections of gradual (1%/yr) future greenhouse gas concentrations (IS92a) [Kattenberg et al., 1996] in the future such that CO2 atmospheric concentration reaches 712 ppm in year 2100. Changes in monthly mean temperature were calculated as differences (2xCO2 climate value - 1xCO2 climate value) and those for monthly precipitation as change ratios (2xCO2 climate value/1xCO2 climate value).
