impacted because many of them have specialized in growing specific crops, which in turn are often highly specialized for the climatic conditions they tolerate (see Figure 1). Longer-term regional climate projections of precipitation, temperature, and soil moisture will allow farmers to decide which crops to focus on in the future and to prepare for investments in new technologies needed to successfully grow new crops.

Mayors of Large Cities

One of the main concerns about climate change is associated with the projected increase in the frequency, duration, and intensity of heat waves. According to the National Weather Service (NWS),“heat is the number one weather-related killer in the U.S.,” b claiming more lives each year than floods, lightning, tornadoes, and hurricanes combined. Heat waves also increase the peak demand for electricity, with the potential for blackouts and the high economic cost associated with them. (Estimates for the August 2003 blackout that affected numerous cities in the United States and Canada ranged from $4 billion to $10 billion [U.S.-Canada Power System Outage Task Force, 2004]). Using a heat index that considers absolute temperature and humidity to assess how hot it really feels, the NWS forecasts extreme heat events several days in advance. This allows city officials to prepare for heat waves by warning the public, instituting energy-saving programs, and designating community cooling centers, reducing some of the negative impacts of heat waves

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FIGURE 1 U.S. Department of Agriculture plant hardiness zone maps are used extensively by gardeners and growers to determine which plants are most likely to thrive at a location. Maps are based on the average annual minimum winter temperature, divided into 10°F zones. The map on the left is based on data from 19741986, and the map on the right is based on data from 1976-2005. The more recent map (right) is generally one half-zone warmer than the previous map (left). SOURCES: http://arborday.org/media/map_change.cfm; http://planthardiness.ars.usda.gov/PHZMWeb/AboutWhatsNew.aspx (both accessed October 11, 2012).



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