Future Climate of the West

See Chapter 6: Glaciers for more about interglacial periods.

By using techniques that help to reconstruct past climates, and by tracking trends in the present, we can predict how current climates might change. Overall, the world is warming, yet, because we are still in an ice age, eventually the current interglacial period should end, allowing glaciers to advance towards the equator again (although likely not for about 100,000 years). However, because the Earth is already getting warmer, the effects of anthropogenic warming are amplified through feedback. Some scientists worry that, if not curbed, human activity could actually disrupt the cycle and knock the planet entirely out of the interglacial period, melting all the ice on Earth.

Causes of Change

While astronomical and tectonic forces will continue to cause climatic shifts, they act so slowly that they will be overshadowed in the near term by human-induced effects. The burning of fossil fuels and removal of forests are the main human activities that alter the composition of the atmosphere. Most dramatically, we are adding huge amounts of carbon dioxide and other greenhouse gases, which trap heat radiated by the Earth. Since plants remove CO2 from the atmosphere, deforestation compounds the issue.

It is extremely difficult to predict the outcome of putting increasing amounts of carbon (as CO2) into the atmosphere, but there are several important reinforcing effects already being observed. The increasing heat is causing glaciers and sea ice around the globe to melt, and as the ground and ocean they covered is exposed, these darker surfaces absorb and re-radiate increasing amounts of heat.

As permafrost in high latitudes melts, the carbon in the soils will become free to enter the atmosphere and, worse, to be converted by bacteria into the even more potent greenhouse gas, methane. Less directly, higher temperatures lead to more frequent and severe droughts, which, in turn, lead to more wildfires that release carbon and aerosols into the atmosphere. Aerosols can have a cooling effect as they reflect away radiation from the sun, but they can also pose a public health hazard.

Water is extremely good at absorbing heat: water vapor is actually the most effective greenhouse gas. Higher temperatures increase evaporation and allow the air to retain more water. While water vapor feedback is the most significant reinforcer of climate warming, water tends to move out of the atmosphere in a matter of weeks—other greenhouse gases linger in the atmosphere for years.

The West contributes significantly to climate change. The population of any industrialized and particularly wealthy country produces pollution. The more than 54 million residents of the West use electricity, transportation, and products that come from carbon-rich fossil fuels. Burning fossil fuels releases carbon into the atmosphere, which warms the Earth. Of the Western states, California emits by far the most greenhouse gases. In 2011 California was the second highest greenhouse gas emitter in the nation, behind only Texas, and the majority of its emissions came from transportation.

On the other hand, Western states are making changes to reduce human impact on the climate. The city of Seattle was an early adopter of the 2030 Challenge, an effort by cities to reduce fossil fuel use in buildings so that both new and renovated buildings would qualify as carbon neutral by the year 2030. Additionally, Washington, California, and Oregon are the top three producers of renewable electric energy in the nation.

Trends and Predictions

Studies show that the West’s climate is changing right now, and that change has accelerated in the latter part of the 20th century. These changes include the following:

  • Temperatures in the West have increased in the last 25 years during all seasons.
  • Nighttime temperatures in the Southwest have increased by almost 1.7°C (3°F) since 1900.
  • The average annual number of wildfires of over 400 hectares (1000 acres) has doubled in California since the 1970s.
  • The freeze-free season in the Northwest is on average 11 days longer for the period of 1991 - 2010, compared with that of 1961 - 1990.
  • Heavy downpours have increased by 18% in the Northwest from 1948 to 2006.
  • Statewide average temperatures in Alaska have increased, with winter temperatures increasing the most: up 3.2°C (5.8°F) from 1949 to 2011.

Climate models predict that the West’s climate will continue to warm, and that the average annual temperature will rise by 2° to 6°C (3° to 10°F) by the end of the 21st century. In Alaska, temperatures are expected to rise more rapidly, by 2° to 4°C (3.5° to 7°F) by the middle of the 21st century. These increased temperatures lead to a whole host of other effects, including drier soils from more evaporation, the increased likelihood of drought and fires, and more rain (rather than snow) in the winter.

Water supply is a critical issue in the West, and communities will need to adapt to changes in precipitation, snowmelt, and runoff as the climate changes. Models predict that winter and spring storms in Nevada will shift northward, dropping less rain and snow in already arid areas. California will likely be faced with less water flowing in its rivers, declining high elevation forests, and expanding grasslands, along with increased pressure on the water supply for agriculture and cities (Figure 9.20).

Figure 9.20: This lake near San Luis Obispo, California contains barely any water following a several-year drought.

Figure 9.20: This lake near San Luis Obispo, California contains barely any water following a several-year drought.

The Northwest is expected to see less summer precipitation and more winter precipitation, and more of the winter precipitation falling as rain rather than snow. Over the past 40 to 70 years, the Cascade Range has experienced a 25% decline in snowpack measured on April 1, a trend that is expected to continue. This means less water from snowmelt in the warm season. Spring runoff in Northwestern streams is expected to occur nearly 20 to 40 days earlier during the 21st century. Sea level rise from melting glaciers and the thermal expansion of a warmer ocean will be a concern for cities such as Seattle, Tacoma, and Olympia (Figure 9.21).

Climate models project that Alaska will receive more precipitation, but that soils will actually become drier due to increased evaporation from warmer air temperatures. Summers are expected to support a longer growing season, and also to see more drought and wildfires. Invasive insects that damage Alaska trees will be better able to survive warmer winters, and will therefore increase and spread. Sea ice will cover the ocean for shorter portions of the year, possibly 284 changing the distribution of plankton blooms, a part of the marine food chain upon which Alaska’s fisheries depend.

Figure 9.21: Maps showing portions of the cities of Olympia and Seattle, Washingrton that will be inundated if sea level rises by one, two, or four feet.

Figure 9.21: Maps showing portions of the cities of Olympia and Seattle, Washingrton that will be inundated if sea level rises by one, two, or four feet.

Hawai’i stands to be significantly impacted by climate change, with serious potential effects on both its ecosystems and economy. Rising temperatures could disrupt the pattern of trade winds, changing rainfall patterns across the islands and creating periods of flooding or drought. Higher temperatures will also place more stress on native plants and animals, enabling the proliferation of invasive species that are better able to withstand temperature extremes. Warming oceans and increased ocean acidity could trigger massive coral die-offs as well as affecting ocean circulation. Finally, sea level rise could inundate much of Hawai’i’s coastline—the worst case scenario of a 2-meter (6-foot) sea level rise would bring Hawai’i’s coast 1.6 kilometers (1 mile) inland in some places, submerging or eroding important economic locations like Waikiki Beach and parts of Honolulu.