Climate Change

It is important to understand that most of the extreme climate change in Earth’s history occurred before humans existed. That being said, the rapid release of carbon dioxide into the atmosphere from human activity is currently causing a global warming event. The warmest overall average state summer tempera-tures in the US are generally found in the South Central (primarily in Oklahoma, Texas, Louisiana, and Arkansas), with the warmest years averaging 28 to 30°C (83 to 86°F) and occasional weeks with maximum temperatures above 37.8°C (100°F). For the last 25 years, these temperature averages have been steadily rising. This seemingly slight increase has been accompanied by more frequent heat waves, shorter winters, and an increased likelihood of drought and wildfires.

The South Central is currently experiencing significant drought throughout, with the worst effects occurring in Texas and Oklahoma (see Figure 10.31). Increased dryness contributes to fire risk—in March 2015, the area northeast of Woodward, Oklahoma experienced a wildfire that consumed more than 9600 hectares (23,000 acres) of land and forced over 125 people to evacuate from their homes. During the major drought and heat wave of 2011, more than 31,000 separate wildfires raged through central Texas, burning a cumulative 1,559,446 hectares (3,853,475 acres) of land and destroying almost 6000 structures.

Water supply is also a critical issue for the South Central states. Much of the area obtains its agricultural and drinking water from aquifers, underground layers of water-bearing permeable rock. The Ogalalla aquifer, part of the High Plains aquifer system, supplies vast quantities of groundwater to Texas, Oklahoma, Kansas, and Nebraska. As drought intensifies and temperature rises, the amount of water drawn from the aquifer (especially for agricultural irrigation) has increased, while the rate at which the aquifer refills has decreased. The aquifer’s average water level has dropped by about 4 meters (13 feet) since 1950, and in some areas of heavy use, the decrease is as high as 76 meters (250 feet) (Figure 10.32). However, the aquifer only replenishes at a rate no greater than 150 millimeters (6 inches) per year. Some estimates indicate that at its current rate of use, the entire Ogalalla aquifer could be depleted by as early as 2028, threatening human lives, our food supply, and the entire Great Plains ecosystem.

Increasing temperatures also allow certain pests, such as ticks and mosquitoes, to live longer, thereby increasing the risk of contracting the diseases they carry. In addition, invasive organisms that damage ecosystems, such as the hydrilla plant in Louisiana, have a better chance to multiply and outcompete native organisms because increased temperatures stress local ecosystems and create an environment more favorable to invasive species.

Another concern regarding hazards exacerbated by climate change in the South Central is whether or not there has been or will be an increase in the number or severity of storms, such as hurricanes and tornados. According to NASA, the present data is inconclusive in terms of whether hurricanes are already more severe, but there is a greater than 66% chance that global warming will cause more intense hurricanes in the 21st century. Since climate is a measure of weather averaged over decades, it might take many years to determine that a change has occurred with respect to these types of storms. Scientists are certain that the conditions necessary to form such storms are becoming more favorable due to global warming.

The Union of Concerned Scientists has created an infographic that demonstrates the relative strength of the evidence that various hazards are increasing as a result of climate change (Figure 10.33).

Figure 10.32: Water level change in the Ogalalla aquifer between 1950 and 2005.

Figure 10.33: The strength of evidence supporting an increase in different types of extreme weather events caused by climate change.