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 West has been accompanied by more frequent heat waves, shorter winters, and an increased likelihood of drought and wildfires. The contiguous Western states are currently experiencing severe drought throughout, with the worst effects occurring in California and parts of Nevada (Figure 10.30). Increased dryness contributes to fire risk—in September 2014, the Eldorado National Forest near Sacramento, California experienced a massive wildfire that consumed more than 39,254 hectares (97,000 acres) of land and required the efforts of more than 8000 firefighters to combat the blaze.
See Chapter 9: Climate to learn more about how climate change will affect the West.
Heat waves are periods of excessively hot weather that may also accompany high humidity. Temperatures of just 3°C (6°F) to 6°C (11°F) above normal are enough to reclassify a warm period as a heat wave. Under these conditions, the mechanism of sweating does little to cool people down because the humidity prevents sweat from evaporating and cooling off the skin. Heat waves have different impacts on rural and urban settings. In rural settings, agriculture and livestock can be greatly affected. Heat stress recommendations are issued to help farmers protect their animals, particularly pigs and poultry, which, unlike cattle, do not have sweat glands.
The impacts of heat waves on urban settings include a combination of the natural conditions of excessive heat and the social conditions of living in a densely populated space. Cities contain a considerable amount of pavement, which absorbs and gives off more heat than vegetation-covered land does. Air conditioning units that cool down the inside of buildings produce heat that is released outside. Pollution from cars and industrial manufacturing also elevates the outdoor temperature in cities. This phenomenon, in which cities experience higher temperatures than surrounding rural communities do, is known as the heat island effect. Other social conditions can cause an increase in the hazards associated with heat waves in urban areas. People who are in poor health, live in apartment buildings with no air conditioning, or are unable to leave their houses are at greatest risk of death during heat waves. In the summer of 2014, California broke a 120-year record for heat, with temperatures 2.5°C (4.6°F) hotter than average. Southern parts of the state also experienced severe heat waves in September and October of that year. The heat wave in September 2014 led to the cancellation of over 20 athletic events, as well as over 100 schools shortening their school days. Los Angeles set a record for daily energy use, as people turned up their air conditioners in an effort to cool down. During the same month, Hawai’i’s electric utilities struggled to generate enough electricity to power an associated spike in energy demand.
Water supply is also a critical issue for the Western states. Much of the West obtains its water from precipitation, snowmelt, and runoff, which will dramatically decrease in quantity as temperature and aridity rise. The Arctic is warming nearly twice as fast as the rest of the planet—summer sea ice around Alaska has decreased by about 12% every decade since the 1970s (Figure 10.31). With melting ice comes an increase in sea level, and all of the Western states except Nevada have a considerable amount of oceanic coastline which will be affected by sea level rise.
Figure 10.31: Extent of Arctic sea ice from 1979 to present. Measurements are made via satellite each September.
Increasing temperatures also allow for certain pests, such as ticks and mosquitoes, to live longer, thereby increasing the risk of contracting the diseases they carry. In addition, invasive insects that damage ecosystems, such as the spruce bark beetle in Alaska, will be better able to survive warmer winters, and will therefore increase and spread.
Another concern regarding hazards exacerbated by climate change in the West is whether or not there has been or will be an increase in the number or severity of storms, such as hurricanes and tornadoes. 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 10.32).