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 seemingly slight increase in the average annual temperatures in the Northwest Central over the past 25 years has been accompanied by more frequent heat waves, shorter winters, and an increased likelihood of drought and wildfires.

Although wildfires can occur during any season, summer fires are the most common, since increased dryness contributes to fire risk. In June 2012, the Fontenelle wildfire in Wyoming’s Bridger-Teton National Forest consumed 25,990 hectares (57,324 acres) of forest after sparks from a downed power line ignited dry, dead timber. In August 2013, a lightning strike ignited the Bear Creek wildfire in Idaho, which burned more than 40,440 hectares (100,000 acres), threatened two popular ski resorts, and required the efforts of more than 1200 firefighters to combat the blaze. The 2012 fire season was among the worst on record in Wyoming, with more than 1300 fires burning about 240,000 hectares (600,000 acres) across the state, thanks to extremely dry conditions and swaths of dead trees killed by pine beetles. Unfortunately, the Rocky Mountains’ rugged terrain can make fires even more difficult to extinguish.

Water supply is also a critical issue for the Northwest Central States. Here, most water is obtained from precipitation, snowmelt, and runoff, which will dramatically decrease in quantity as temperature and aridity rise. In addition, Nebraska obtains much of its agricultural and drinking water from the Ogalalla aquifer, an underground layer of water-bearing permeable rock. Part of the High Plains aquifer system, this underground reservoir supplies vast quantities of groundwater to Nebraska as well as Texas, Oklahoma, and Kansas. 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 recharges 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 10.33). However, the aquifer only replenishes at a rate no greater than 150 millimeters (6 inches) per year. While the portion of the aquifer beneath Nebraska has yet to be adversely affected, 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.

Figure 10.33: Water level change in the Ogalalla aquifer between 1950 and 2005.

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 mountain pine beetle, have a better chance of multiplying and outcompeting 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 Northwest Central is whether or not there has been or will be an increase in the number or severity of storms, including thunderstorms and tornados. According to NASA, the present data is inconclusive in terms of whether major storms are already more severe, but there is a greater than 66% chance that global warming will cause more intense storms 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, however, 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 10.34).

Figure 10.34: The strength of evidence supporting an increase in different types of extreme weather events caused by climate change.