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The global rise in temperatures will affect different locations on earth in unique ways. Scientists have identified the Southwest as a climate change hotspot—an area whose climate is particularly vulnerable to an increase in greenhouse gases in the atmosphere (Diffenbaugh et al. 2008). The models used by the US Global Change Research Program indicate that the average annual temperature in the Southwest may increase by 4 to 10 degrees Fahrenheit, compared to temperatures between 1960 and 1979. Atmospheric circulation patterns are likely to change, causing southwestern climate to become more arid overall (Christensen et al. 2007, Seager et al. 2007). The aridity may become much worse during La Niña events, causing droughts that may be more severe than any other droughts seen in the climate record, including the medieval megadroughts (Seager et al. 2007, Dominguez et al. 2009). The Southwest may also experience more frequent and longer-lasting heat waves, and the precipitation that does fall is more likely to come from extreme precipitation events (Diffenbaugh et al. 2005). Human- caused changes in winter climate appear to be happening already: over the past 50 years, natural climate variability alone could account for only 40% of the changes observed in snow pack, winter air temperatures, and spring streams in the West (Barnett et al. 2008). These results indicate that if humans continue to emit greenhouse gases, future climate will continue to be outside the normal range of variability.
The seasonality and variability of the precipitation is likely to shift, too. Because of the effect of greenhouse gas emissions on climate, spring has been arriving earlier over the past 50 years, and this trend is likely to continue (Bonfils et al. 2008, Cayan et al. 2001, Stewart et al. 2004). The dry spring season is expected to begin earlier in the year because models predict that the late-winter storm track over the western United States may weaken and shift northward (McAfee and Russell 2008, Seager et al. 2007). If the dry-season is lengthened, severe droughts may occur more often. Drought effects could be amplified by increased variation in year-to-year winter precipitation. Although this variability has not yet been modeled for the future, it has been analyzed for the past 40 years. The analysis found that extreme reversals in winter precipitation from year to year have increased since 1960 (Goodrich and Ellis 2008). For example, the winter of 2004/2005 was the wettest winter on record, but the winter the following year was the driest winter on record. Winter precipitation is far easier to predict than monsoon precipitation because winter storms are large and follow storm tracks, but the monsoon storms are localized and their occurrence is influenced by topography. Therefore, current climate models cannot accurately predict the effect of climate change on the monsoon (Lenart 2007)."
The global rise in temperatures will affect different locations on earth in unique ways. Scientists have identified the Southwest as a climate change hotspot—an area whose climate is particularly vulnerable to an increase in greenhouse gases in the atmosphere (Diffenbaugh et al. 2008). The models used by the US Global Change Research Program indicate that the average annual temperature in the Southwest may increase by 4 to 10 degrees Fahrenheit, compared to temperatures between 1960 and 1979. Atmospheric circulation patterns are likely to change, causing southwestern climate to become more arid overall (Christensen et al. 2007, Seager et al. 2007). The aridity may become much worse during La Niña events, causing droughts that may be more severe than any other droughts seen in the climate record, including the medieval megadroughts (Seager et al. 2007, Dominguez et al. 2009). The Southwest may also experience more frequent and longer-lasting heat waves, and the precipitation that does fall is more likely to come from extreme precipitation events (Diffenbaugh et al. 2005). Human- caused changes in winter climate appear to be happening already: over the past 50 years, natural climate variability alone could account for only 40% of the changes observed in snow pack, winter air temperatures, and spring streams in the West (Barnett et al. 2008). These results indicate that if humans continue to emit greenhouse gases, future climate will continue to be outside the normal range of variability.
The seasonality and variability of the precipitation is likely to shift, too. Because of the effect of greenhouse gas emissions on climate, spring has been arriving earlier over the past 50 years, and this trend is likely to continue (Bonfils et al. 2008, Cayan et al. 2001, Stewart et al. 2004). The dry spring season is expected to begin earlier in the year because models predict that the late-winter storm track over the western United States may weaken and shift northward (McAfee and Russell 2008, Seager et al. 2007). If the dry-season is lengthened, severe droughts may occur more often. Drought effects could be amplified by increased variation in year-to-year winter precipitation. Although this variability has not yet been modeled for the future, it has been analyzed for the past 40 years. The analysis found that extreme reversals in winter precipitation from year to year have increased since 1960 (Goodrich and Ellis 2008). For example, the winter of 2004/2005 was the wettest winter on record, but the winter the following year was the driest winter on record. Winter precipitation is far easier to predict than monsoon precipitation because winter storms are large and follow storm tracks, but the monsoon storms are localized and their occurrence is influenced by topography. Therefore, current climate models cannot accurately predict the effect of climate change on the monsoon (Lenart 2007)."