Future Climate

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 toward 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. In 1956, NOAA established the Mauna Loa Observatory (MLO) in Hawai’i to measure a variety of atmospheric parameters, including carbon dioxide (CO2) concentration. The CO2 record extends from 1958 to present, and it shows the influence of both natural and anthropogenic processes (Figure 9.12). The zigzag pattern is the result of seasonal photosynthesis in the northern hemisphere. In spring and summer, the growth and increased photosynthetic activity of plants draws CO2 out of the atmosphere. Conversely, it accumulates in the atmosphere during fall and winter when plants are dormant. The overall upward trend is caused by human activity. Industrialization, fossil fuel combustion, and deforestation all contribute CO2 to the atmosphere, adding it at a rate much faster than natural processes can remove it. Analyses of ancient atmosphere samples preserved in glacial ice cores show CO2 levels to be 180 parts per million (ppm) at the height of the last ice age and 280 ppm at its end. The amount of CO2 in the atmosphere has been increasing at a rapid rate since the start of the industrial revolution, and it has accelerated since the end of World War II. In May 2013, measurements at MLO reached 400 ppm CO2 for the first time.

Figure 9.12: Measured concentration of atmospheric carbon dioxide (1958 to present) at MLO.

Figure 9.12: Measured concentration of atmospheric carbon dioxide (1958 to present) at MLO.

While some atmospheric carbon dioxide is necessary to keep Earth warm enough to be a habitable planet, the unprecedentedly rapid input of CO2 to the atmosphere by human beings is cause for concern. Everything we know about atmospheric physics and chemistry tells us that increased CO2 leads to a warmer planet. Multiple paleoclimate data sets verify this conclusion, and modern measurements confirm that we are living in an increasingly warmer world. 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, carbon in the soil becomes 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, such as carbon dioxide and methane, linger in the atmosphere for years.

The Northwest Central US contributes to climate change, although its total greenhouse gas emissions are lower than those of other areas of the United States. The population of any industrialized and particularly wealthy country produces pollution; the majority of these emissions come from the use of petroleum. The 6.5 million residents of the Northwest Central 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 Northwest Central States, Wyoming emits the most greenhouse gases, releasing 64 million metric tons of carbon dioxide per year. By contrast, the highest greenhouse gas-emitting state in the nation is Texas, which releases nearly 656 million metric tons of CO2 per year. Idaho is one of the lowest carbon emitters in the nation, producing only 16 million metric tons of CO2 annually. However, the Northwest Central’s low emissions profile is related to its low population. For example, Wyoming has fewer than 600,000 residents; in 2011 it emitted 113 metric tons of CO2 per capita, the highest in the nation, while Texas, with a population of 26 million, emitted only 23 metric tons per capita.

Although the Northwest Central still has a relatively low carbon footprint, its greenhouse gas emissions have been growing. As recently as 1990, Montana was estimated to be a net carbon sink, with carbon sequestered in its forests and soils. By 2005, it had become a net carbon emitter, and carbon emissions in other Northwest Central States have increased as well. Over the period from 2000 to 2011, Nebraska experienced a 25% increase in the amount of CO2 it emitted—the greatest absolute increase in the country—due to an increasing amount of fossil fuel-related energy production.

See Chapter 7: Energy to learn about energy production in each of the Northwest Central states.

On the other hand, many Northwest Central States are also making changes to reduce human impact on the climate. Boise, Idaho, Big Sky, Montana, and Jackson, Wyoming are just a few locations that have adopted 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, many states are stepping up their use and production of renewable energy. Montana ranks ninth in the nation for renewable energy production, most of which it generates from hydroelectricity.

Trends and Predictions

Studies show that climate in the Northwest Central is changing right now, and that change has accelerated in the latter part of the 20th century (Figure 9.13). These changes include the following:

  • During the 20th century, the average annual temperature of the Northwest Central US as a whole increased by 0.9°C (1.6°F). North Dakota’s average temperature increased 1.9°C (3.4°F) during the last 130 years, the fastest increase in the US.
  • Soils in Nebraska have become warm enough to plant corn one to three weeks earlier in the 2000s compared to in the 1990s.
  • Springtime snowmelts in Wyoming in 1990 were flowing four days earlier than in 1950.
  • The Ogalalla Aquifer, which provides fresh water to most of Nebraska, has been depleted by more than 40% in some areas, thanks to years of decreased rainfall.
  • The bull trout, an endangered freshwater fish native to northwestern North America, is estimated to have lost 11% of its stream habitat in Idaho’s Boise River Basin due to an increase in water temperature.
  • In the last century, annual precipitation has increased by up to 20% in South Dakota.
  • In 1850, Montana’s Glacier National Park contained an estimated 150 glaciers. Today, only 25 glaciers remain. Models predict that all of them will have disappeared by 2030.
Figure 9.13: Global temperature change since the 1880s. The Earth’s average surface temperature has progressively risen over the last five decades.

Figure 9.13: Global temperature change since the 1880s. The Earth’s average surface temperature has progressively risen over the last five decades.

Climate models predict that the Northwest Central’s climate will continue to warm, and that the average annual temperature in most of the area will rise by 3°C to over 6°C (6°F to over 10°F) by the end of the 21st century. These increased temperatures lead to a whole host of other effects, including drier soils from greater evaporation, and the increased likelihood of drought and fires. In Montana, for example, the annual amount of wildfire-prone land area is predicted to increase by nearly 400% by the end of the century.

Water supply is a critical issue in the Northwest Central US, and communities will need to adapt to changes in precipitation, snowmelt, and runoff as the climate changes. Models predict that much of the area’s climate will become wetter, with more precipitation falling in winter and spring. In Idaho, it’s likely that increasingly more precipitation will fall as rain rather than snow, and snow in the mountains will melt earlier in the spring. This could strain the water supply in the warm season. Additionally, because higher temperatures mean greater evaporation and warmer air can hold more water, precipitation will occur in greater amounts at a time (Figure 9.14). During the cooler spring this will lead to flooding, while in hot summers, droughts will become more frequent. These drier summers and wetter winters and springs could have significant adverse impacts—drier summer days and higher temperatures will amplify evaporation, increasing the risk of desertification and affecting natural ecosystems as well as increasing pressure on the water supply for agriculture and cities.

Figure 9.14: Changes in heavy precipitation events from the 1900s to the 2000s. Each event is defined as a two-day precipitation total that is exceeded, on average, only once every five years. The occurrence of such events has become increasingly common.

Figure 9.14: Changes in heavy precipitation events from the 1900s to the 2000s. Each event is defined as a two-day precipitation total that is exceeded, on average, only once every five years. The occurrence of such events has become increasingly common.

Agriculture is a huge industry in the Northwest Central US, especially in the Great Plains and Central Lowland. To the advantage of soybean and corn growers in Nebraska, warmer temperatures and increased precipitation have helped bring on longer growing seasons. Warmer temperatures, however, also make it easier for insect pests to overwinter and produce more generations. The European corn borer, a devastating pest found in the central and eastern US, produces more generations in warmer parts of the country (Figure 9.15).

Figure 9.15: The European Corn Borer, an agricultural insect pest, currently produces one to four generations a year depending on its location in the US. As the climate warms farther north, they are expected to produce more generations in the Great Plains and Central Lowland, causing greater crop damage.

Figure 9.15: The European Corn Borer, an agricultural insect pest, currently produces one to four generations a year depending on its location in the US. As the climate warms farther north, they are expected to produce more generations in the Great Plains and Central Lowland, causing greater crop damage.

As the Great Plains and Central Lowland warm, one can expect three or four generations of these pests annually in regions that previously had only one or two. Another major pest affected by the warming climate is the mountain pine beetle, which has been devastating pine forests throughout the Pacific Northwest and Canada, and is now spreading west into Montana, Wyoming, and the Dakotas. In the last few years, the beetle’s numbers have spiraled out of control thanks to warmer temperatures, which extend the breeding season and generate fewer cold-related dieoffs for the insect population. So far, 36 million hectares (88 million acres) of pine forest have been affected, with a 70 - 90% tree mortality rate (Figure 9.16). The death of these trees will have a significant impact on the forests’ ability to sequester carbon; researchers have estimated that the dieoffs in Canada alone will have caused the release of 270 million metric tons of CO2 into the atmosphere by 2020.

Figure 9.16: A swath of dead trees in the Black Hills of South Dakota, destroyed by the mountain pine beetle.

Figure 9.16: A swath of dead trees in the Black Hills of South Dakota, destroyed by the mountain pine beetle.

The causes of specific weather events such as hurricanes and severe thunderstorms are incredibly complex, although climate change has enhanced some correlated factors, such as increased wind speed and an unstable atmosphere. Higher atmospheric moisture content has also been correlated with an increased incidence of tornados and winter storms. However, although climate change is predicted to enhance the intensity of severe weather, there is currently no way to calculate what effect climate change will have on the frequency of specific storm events—for example, we might see more powerful tornados, but we do not know if we will see more of them.

All over the Northwest Central US, residents and communities have begun to adapt to climate change, and to plan for future changes that are expected to come.