ClimateChange Assessment Guide.pdf - University of Waterloo

Future Climate Scenarios21Figure 3.2 Development of climate models through incorporation of new components/processes ((Albritton et al., 2001)Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of theIntergovernmental Panel on Climate Change, Box 3, Figure 1. Cambridge University Press)however, improvements have also continued in existingcomponents and model resolution - in the vertical foratmosphere and ocean layers, and in the horizontal gridspacing. Developments in GCMs have been limited bycomputing capability as well as understanding of thephysical processes that influence climate.A complementary development to GCMs is limited-areamodelling or a regional climate model (RCM). RCMscover only a portion of the globe, use a finer scalegrid than GCMs and incorporate smaller-scale physicalprocesses particularly interactive land-surface models.RCMs are discussed in more detail in Chapter 4 alongwith other methods for developing local scale climatedata.The performance of GCMs in reproducing featuresand trends of past and recent climate is treatedextensively in Bader et al. (2008) and Randall et al.(2007). The availability of the CMIP3 results allowed forthe development of metrics from a wide range of GCMoutput to compare model results (Gleckler et al., 2008;Randall et al., 2007). Current climate models simulate theseasonal cycle and large-scale geographical variationsin surface temperature very well; correlation betweenobserved and modelled temperature is 95% or better(CCCP, 2008) (Covey et al., 2003). These models arealso very good at simulating storms and jet streams inthe mid latitudes. Simulation of precipitation, however,remains a challenge with a correlation of only about 50to 60% for seasonal mean precipitation at the scale ofa few hundreds of kilometres (CCCP, 2008; Covey et al.,2003). When precipitation is sorted into light, moderateand heavy categories, models reproduce the observedextent of moderate precipitation (10 to 20 mm/day)but underestimate that of heavy precipitation andoverestimate the extent of light precipitation (Dai, 2006).An emerging area of research is the development ofquantitative metrics to assess the performance of GCMsin simulating large-scale climatological features toprovide information to aid in the selection of GCMs forclimate change scenario development (Gleckler et al.,2008; Randall et al., 2007). It is not clear what aspectsof current climate need to be well simulated in order toprovide the best projections of future climate (Gleckler