Future Climate of the South Central

By using some of the 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. In 1956, NOAA established the Mauna Loa Observatory (MLO) in Hawai’i to measure a variety of atmospheric parameters, including carbon dioxide concentration. The CO₂ record extends from 1958 to present, and it shows the influence of both natural and anthropogenic processes (Figure 9.11). 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 9.11: Measured concentration of atmospheric carbon dioxide (1958 to present) at MLO.

While some atmospheric CO₂ 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 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, such as carbon dioxide and methane, linger in the atmosphere for years.

The South Central contributes significantly to climate change. The population of any industrialized and particularly wealthy country produces pollution. The 48 million residents of the South 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 South Central States, Texas emits by far the most greenhouse gases. The highest greenhouse gas emitter in the nation, Texas releases nearly 656 million metric tons of CO₂ per year, nearly double that of California, the second largest emitter. The majority of these emissions come from the use of petroleum.

On the other hand, South Central States are making changes to reduce human impact on the climate. Texas’ emissions have decreased by 65 metric tons (64 standard tons) in the last decade, the greatest absolute reduction in of any state over that time period. The city of Dallas 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, many states are stepping up their use and production of renewable energy. Missouri ranks 17th in the nation for renewable energy use, most of which it produces from biomass.

Trends and Predictions

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

• The number of days with temperatures above 35°C (95°F) has been steadily increasing for the last 25 years (Figure 9.12).

• The city of St. Louis experiences about four heat waves lasting three days or longer each summer—a number which has doubled over the last 60 years.

• Locations along the Gulf of Mexico have experienced over 8 inches of sea level rise in the last 50 years.

• In 2011, Texas experienced the worst one-year drought in state history, exacerbated by temperatures almost 3°C (5°F) above normal. The drought cost the state $7.6 billion in agricultural losses.

• The Ogalalla Aquifer, which provides fresh water to much of the South Central, has been depleted by more than 40% in some areas, thanks to years of decreased rainfall.

• Altered flowering patterns due to more frost-free days have increased the South Central’s pollen season for ragweed, a potent allergen, by 16 days since 1995.

Figure 9.12: 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 South Central will continue to warm, and that the average annual temperature will continue to increase for the foreseeable future—likely a 3°C (5°F) increase by 2100. Summer temperatures in Oklahoma, for example, are expected to increase by 3 to 6°C (6 to 10°F) by 2100. These increased temperatures lead to a whole host of other effects, including drier soils from more evaporation, and the increased likelihood of drought and fires. Texas, which contains the largest acreage of crop-, pasture-, and rangeland in the United States, could be severely impacted by these changes. Because higher temperatures mean greater evaporation and warmer air can hold more water, precipitation will occur in greater amounts at a time, but less frequently (Figure 9.13). 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 on agriculture.

Water supply is a critical issue in the South Central, and communities will need to adapt to changes in precipitation, snowmelt, and runoff as the climate changes. Drier days and higher temperatures will amplify evaporation, increasing the desertification of already arid areas and affecting natural ecosystems as well as increasing pressure on the water supply for agriculture and cities (Figure 9.14).

Figure 9.13: 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: Dead fish rot on the cracked lakebed of the O.C. Fisher Reservoir at San Angelo State Park, Texas. The lake, which once spanned more than 2200 hectares (5400 acres), was once an important source of drinking water as well as a recreational fishing area. It is now completely dry due to severe drought conditions.

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.

More than 50% of the American population currently lives in coastal regions. With increased global warming, sea-level rise and the likelihood of increased incidences of extreme weather are expected, including an increase in hurricane intensity and associated storm surge. Sea level rise from melting glaciers and the thermal expansion of a warmer ocean will be a concern for populated coastal areas, including major cities such as New Orleans (Figure 9.15) and Houston. Regional studies project that by 2030, climate change could cause $4.6 billion in damages to coastal property and assets on the Gulf Coast alone.

Figure 9.15: Land loss in coastal Louisiana between 2010 and 2060, according to projections consistent with a sea level rise of 27 centimeters (10.6 inches) (left) and 80 centimeters (31.5 inches) (right).