Emissions Scenario-Based Analyses of Projected Extreme Heat and Energy Costs in Southwestern United States

Summer temperatures in the southwest U.S. are projected to increase more rapidly than previously expected, accompanied by longer, more frequent, and more severe extreme heat conditions. This study is based on two Atmosphere-Ocean General Circulation Models, the HadCM3 and the PCM. These were forced with the A1FI (higher) and B1 (lower) greenhouse gas emissions detailed in the IPCC Special Report on Emission Scenarios, and were statistically downscaled to specific urban locations for impacts assessments. Results show summer average temperature increases of 2-5oC under the lower B1 scenario and 4-8oC under the higher A1fi scenario. As heat waves become longer and more frequent, projections for California indicate the heatwave onset will occur by as much as 30 days earlier than present by 2050 and 70 days earlier by 2099. In addition, the number of heat wave days for six major metropolitan areas (Los Angeles, Riverside/San Bernardino, San Francisco, Sacramento, Albuquerque and Phoenix) show an increase by 15 to 40 more days in the 2050s than during the 1990s, and by the 2090s, the increase in heatwave days rises by 30 to 50 days under B1 and 70 to 100 days under A1fi. Heat waves are also projected to become more intense, with higher temperatures sustained over longer periods.

Increases in mean and extreme heat events during the summer months have significant implications for energy demand in the already air-conditioned Southwest. Electricity load in these areas have a strong correlation with temperature and increases proportionally due to air conditioning use. California's power grid is already strained as temperatures increase, as this recent summer has seen energy alerts for Southern California. The projected temperature increases discussed here are likely to further strain the California power grid requiring a combination of increased energy efficiency, conservation, and alternative energy sources.