Confronting Climate Change in the Great Lakes Region. Technical Appendix Climate Change Projections CLIMATE MODELS

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1 Confronting Climate Change in the Great Lakes Region Technical Appendix Climate Change Projections CLIMATE MODELS Large, three-dimensional, coupled atmosphere-ocean General Circulation Models (GCMs) of the Earth's climate system are the reference standard for global change research. These models incorporate the latest understanding of the physical processes at work in the atmosphere, oceans, and the Earth s surface. Models are constantly being enhanced (see Figure 1) as our understanding of climate improves and as computational power increases, enabling additional components of the Earth-oceanatmosphere system to be dynamically linked. Figure 1. Schematic diagram showing the development of climate models from the mid s to the present date. Source: IPCC, 2001 Using the Intergovernmental Panel on Climate Change s 2000 standard emission scenarios as input, current models estimate global temperature to increase by 2.5ºF to 10.4ºF (1.4ºC to 5.8ºC) by It is certain that the rate of temperature change will be faster than any since at least the end of the last ice age, ten thousand years ago. Annual and regional changes have the potential to far exceed these values as they respond to natural variability and to local conditions. It is also certain that precipitation will change, with some regions becoming drier and others wetter. Projected intensification of the hydrological cycle increases the threat of more floods, although how this intensification will affect different regions is likely to vary considerably. Likewise, changes in precipitation patterns bring the threat of more extreme droughts to some regions while others may experience fewer droughts.

2 While today s state-of-the-art GCMs are generally in good agreement concerning globally-averaged climate projections, regional changes in climate are more difficult to predict because the extrapolation from global to local scales is not precise. In particular, these models lack sufficient spatial resolution to capture the orographic drivers of local climate variations such as mountain ranges or lakes. However, these results still allow for determination of gradients and general trends across the region of interest. To date, results from global-scale general circulation models remain the best means of evaluating regional changes in climate. In the future, studies such as this one will be enhanced through the use of regional climate models driven by 6-hr output from global models, currently under development. At the present time, however, our confidence in available climate projections can already be improved through comparison of results between reliable models driven by the same emission scenarios (see below). Figure 2. Schematic diagram of the primary components of the PCM model. (Source: Previous assessments of regional impacts have been based on the results of models from the early and late 1990 s. In contrast, this analysis uses results from two of the latest generation of general circulation climate models: the Parallel Climate Model (PCM), recently developed at the U.S. National Center for Atmospheric Research and funded by the U.S. Department of Energy (Figure 2, Washington et al., 2000) and the HadCM3 model, developed at U.K. Meteorological Office s Hadley Centre for Climate Modeling (Figure 3, Gordon et al., 2000; Pope et al., 2000). Both PCM and HadCM3 are three-dimensional climate models, with a resolution of 2.5 o latitude by 2.5 o longitude for PCM and 2.5 o latitude by 3.75 o longitude for HadCM3, as illustrated in Figure 3. This means that the PCM model covers Great Lakes area with 48 grid boxes, while the HadCM3 model covers the area with 49 boxes. More information is available on-line at: and

3 Figure 3. Schematic diagram of the HadCM3 model resolution andits primary components. (Source: Viner, 1998, 2002) A detailed comparison of observed temperature and precipitation patterns with model calculations over the reference period of reveals that, despite its relatively coarse resolution, the HadCM3 model does an adequate job of capturing the observed distribution of temperature and precipitation over the Great Lakes region (Figures 4 and 5). This comparison also revealed three biases in HadM3 model calculations relative to historical data that must be kept in mind when analyzing future projections: modeled average winter temperatures are approximately 5-10 o F lower than observed; modeled average summer temperatures in the northern part of the region are 1-5 o F higher than observed; and modelled average precipitation throughout the year is slightly higher (~0.1 mm/day) than observed. In regards to this bias, two important points must be made. First, detailed historical data for the reference period was used to eradicate model biases to the extent this was possible. Second, the projections presented in this report are for the change in temperature relative to baseline, not absolute temperatures. If it is assumed that changes in model bias between the beginning and the end of the century, though existent, are secondary in comparison to the change in temperature projected to occur over the same time period, the greater part of model bias can be removed by considering relative rather than absolute change.

4 Figure 4. Comparison of HadCM3 modelled temperature for winter (DJF) and summer (JJA) with observed data for the reference period ( o F). Figure 5. Comparison of HadCM3 modelled precipitation for winter (DJF) and summer (JJA) with observed data for the reference period (mm/day).

5 Both the PCM and the HadCM3 models have run the two SRES mid-range scenarios, A2 and B2. Model results for these scenarios, shown in Figures 6 and 7, are in good agreement for winter temperatures (within 2 o F) while summer temperatures differ by up to 6 o F by the end of the century, with the HadCM3 model predicting higher summer temperatures than the PCM. HadCM3 and PCM projections of precipitation changes for the A2 scenario are in good agreement for both seasons, averages over the Great Lakes region projected to display an increase in winter and a slight decrease in summer. In addition to these mid-range scenarios, the HadCM3 model has also run the A1FI (high emissions) and B1 (low emissions) scenarios. The wider range of climate change projected by the high and low scenarios are used to explore the possible extent of climate change impacts on various sectors, keeping in mind the differences between the models for the mid-range scenarios. Figure 6. Comparison of HadCM3 and PCM temperature projections for winter (DJF) and summer (JJA). Temperature change is shown relative to average for that season.

6 Figure 7. Comparison of HadCM3 and PCM projections of change in precipitation for winter (DJF) and summer (JJA). Percentage change in precipitation is shown relative to for that season.

7 Additional comparisons between HadCM3 projections for the Great Lakes region and those of other climate models are made possible by a comparison tool hosted by the Canadian Institute for Climate Studies ( scenarios/plots/select.cgi). The current version of this tool only permits comparison of one selected point in space. To compare model performance over the Great Lakes region, 5 gridpoints were selected as indicated in Figure 8, centered at: Latitude ( o N) Longitude ( o W) Figure 8. Map of Great Lakes region indicating locations of grid points at which intermodel comparisons were made. 5 Eight models are compared in the following plots, consisting of: CGCM1 and 2 HadCM2 and 3 ECHAM4 CSIRO mk2b CCSR98 GFDLr15 3 Model projections of temperature/precipitation change for greenhouse-gas-only (GG) and greenhouse gas/aerosol scenarios (GA) are compared for three decades (2020 s, 2050 s and 2080 s) and two seasons (winter/djf and summer/jja). The models used for the US National Assessment are blue (HadCM2) and black (CGCM1). HadCM3 results are yellow, while PCM results are not available for this comparison.

8 WINTER (DJF) PROJECTIONS FOR THE 5 GRID POINTS 1 Near-term (2020 s) Mid-term (2050 s) Long-term (2080 s)

9 SUMMER (JJA) PROJECTIONS Near-term (2020 s) Mid-term (2050 s) Long-term (2080 s)

10 Points to note are the following: For short-term projections (2020 s), model responses appear randomly scattered For long-term projections (2080 s) model results migrate towards the lower right-hand side of the plot, suggesting hotter and drier conditions under increasing forcing (except for winter in northernmost grid box #5) The primary exception to this trend is the HadCM2 model whose runs remain primarily in the upper left-hand side of the plot, indicating that its projections lie at the cooler and wetter end of the range of possible change in the Great Lakes region Relative to other models, HadCM3 temperature projections tend to show a smaller response in winter and a similar or greater response in summer Relative to other models, HadCM3 precipitation projections appear to be mid to high for winter and mid to low for summer PCM results are not available for this intercomparison, although Figures 6 and 7 suggest that PCM precipitation is similar to that of HadCM3, and PCM temperature projections may be at the lower end of the range for both winter and summer

11 References Gordon, C., Cooper, C., Senior, C.A., Banks, H., Gregory, J.M., Johns, T.C., Mitchell, J.F.B. and Wood, R.A.: 2000, The simulation of SST, sea ice extents and ocean heat transports in a version of the Hadley Centre coupled model without flux adjustments, Climate Dynamics 16, Intergovernmental Panel on Climate Change: 2001, Climate Change 2001: The Scientific Basis, J.T. Houghton and D. Yihui (eds.), Cambridge, Cambridge University Press. Pope, V. D., Gallani, M. L., Rowntree, P. R. and Stratton, R. A.: 2000, The impact of new physical parametrizations in the Hadley Centre climate model -- HadCM3, Climate Dynamics 16, Washington, W.M., Weatherly, J.W., Meehl, G.A., Semtner Jr., A.J., Bettge, T.W., Craig, A.P., Strand Jr., W.G., Arblaster, J.M., Wayland, V.B., James, R. and Zhang, Y.: 2000, Parallel climate model (PCM) control and transient simulations, Climate Dynamics 16,