Future Climate of the Midwest

The Earth’s orbit, tilt, and wobble alter its position with respect to the Sun, affecting the global climate. These changes in the Earth’s movement are cyclical, and the changes in Earth’s climate associated with them are known as Milankovitch Cycles.

While climate describes conditions over a long period of time, it does change, however slowly. In a previous section of this chapter, past changes were discussed. Using some of the techniques that help to reconstruct past climates, plus 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 will end, and glaciers will begin advancing towards the equator again, although likely not for about 100,000 years. Because the Earth is already getting warmer, the effects of anthropogenic sources of 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.

See Chapter 6: Glaciers for more about interglacial periods.

Causes of Change

While astronomical and tec- tonic forces will continue to cause climates to change, their work is so slow that it will be overshadowed in the near term by human-induced effects. The burning of fossil fuels, removal of forests, and all manner of human activities are altering 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 carbon dioxide from the atmosphere, deforestation compounds the issue.

There is a finite amount of carbon on the planet, and the ways in which it changes states and locations are almost innumerable. This makes it extremely difficult to predict the outcome of putting increasing amounts of carbon (as carbon dioxide) 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 the most effective greenhouse gas. Higher temperatures allow more water to be held in the air, as well as increase evaporation. 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 Midwest has a unique combination of contributors to climate change. The population of any industrialized, and particularly wealthy, country produces pollution. The more than 50 million residents of the Midwest use electricity, transportation, and products that come from carbon-rich fossil fuels. But it is also a major center for agriculture, manufacturing, and coal, gas, and biofuel production, each of which release greenhouse gases. The Midwestern states are also developing unique ways to curb their effect on the climate. Minnesota has some of the most aggressive energy objectives in the US and is on track to produce 25% of its energy from clean fuel sources by 2025. In fact, Minnesota and Iowa already produce more than 10% of their energy from wind and, along with Wisconsin, 50% from biofuel! A distinction should, however, be drawn between production and consumption—these states consume far more coal and natural gas than anything else.

Temperature, Precipitation, and Storms

The average temperature in the Midwest is predicted to continue to increase for the foreseeable future—likely 3°C (5°F) by 2100. Of course, this doesn’t mean this will occur steadily or evenly. For example, since 1980, the average annual temperature for northern Illinois has increased from around 7°C (45°F) to 9°C (49°F), a change of 2°C (4°F), yet the average winter temperature has increased by 4°C (8°F)! Perhaps because of its distance from the moderating influence of the oceans, the Midwest appears to be affected by warming more quickly than are many other areas. Interestingly, higher temperatures and higher carbon dioxide levels are, up to a point, expected to extend the growing season and increase crop yields. The US Government’s Global Change Research Program expects the plant hardiness zones for the Midwest to become warmer by up to one zone every 30 years, rapidly changing what kinds of plants and crops can survive. Translating this change to the Köppen climate classification, much of the Midwest will soon be redesignated as humid subtropical. Coupled with less precipitation overall, a garden you planted in Michigan as a child will look like one from Arkansas by the time you are an adult, and then like one from Texas after 30 more years!

We can also expect more incidences of extreme weather. The causes of specific weather events are incredibly complex, but strong correlations and consequences from climate change are already apparent, and they offer clues about what to predict. Because higher temperatures mean greater evaporation and the ability of the air to hold more water, precipitation will occur in greater amounts at a time, but less frequently. During the cooler spring this will lead to flooding, while in hot summers, droughts will become more frequent. Higher atmospheric moisture content has also been correlated with an increased incidence of tornados—a particular concern in the Midwest.