Climate Change in the Southwest
Observed Climate Changes
Thermometers and weather stations positioned around the globe paint a clear picture: the mercury is rising. Since about 1900, when the number of weather stations became sufficient to depict regional and global trends, temperatures have increased by about 1.5 degrees Fahrenheit (Figure 1). More recently, temperature increases have accelerated to the tune of about 0.35 degrees F per decade in the last 30 years. It has not, however, been a smooth ride. Natural climate variability like El Niño–Southern Oscillation (ENSO) and volcanic eruptions influence the amount and the mechanism by which energy is distributed around the globe and have caused dips and spikes in global temperature.
Average annual temperature in the Southwest has mimicked the global pattern. Seasonal patterns are also important as some processes respond to climate of specific periods. For example, snow melt in the spring, and observed increases in this season’s temperatures have caused the peak in streamflow to occur earlier in the year and the amount of snow measured on April 1 to decline.
Changes in precipitation are also discernable. Since 1958, average annual precipitation has decreased in most of Arizona but has increased in New Mexico (Figure 2).
There also have been indications that the strong westerly jet stream that directs storms in the Southwest during the winter has shifted north in the spring since the 1970s. Less precipitation and warmer conditions worsen drought, which is natural and common to the area. A comparison of the drought experienced in the early 1950s to the recent drought period between 2000 and 2003, for example, suggests that a major difference is that temperatures in the spring and early summer are warmer in the 2000s, which more rapidly parches the landscape and primes it for fires, among other potential impacts.
Indicators of changes in the climate range from shifts in the timing of flower blooms to the amount of water continue in snowpack to the number of heat waves and days with temperatures that exceed 100 degrees F.
Southwest Climate Change Network
CLIMAS has developed a Web resource specific to the issue of climate change because the Southwest is sensitive to climate change and is exhibiting dramatic changes that have widespread impacts. The Southwest Climate Change Network (SWCCN) features information on the science, impacts, and solutions along with news feeds, a blog from scientists, and other informational resources.
Figure 1. Average annual global temperature between 1880–2009. Data analyzed and presented by the NASA Goddard Institute for Space Studies.
Figure 2. Observed changes in Annual average precipitation between 1958–2008. Image courtesy of the U.S. Global Climate Research Program, 2009.