Adapted from: Global Climate Impacts in the United States. T.R. Karl, J.M. Mellilo, and T.C. Peterson (eds.). Cambridge University Press, 2009. Available online at USGCRP
In the Midwest, precipitation has increased along with temperature in recent decades. Average temperatures in the Midwest have risen, with the largest increases in winter. The length of the frost-free or growing season has been extended by one week, mainly due to earlier dates for the last spring frost. Since the 1980s, large heat waves have become more frequent than any time in the last century, other than the Dust Bowl years of the 1930s.
Heavy downpours are now twice as frequent as they were a century ago. Both summer and winter precipitation has been above average for the last three decades, the wettest period in a century. The Midwest has experienced two record-breaking floods in the past 15 years. There has also been a decrease in lake ice, including on the Great Lakes. The observed patterns of temperature increases and precipitation changes are projected to continue, with larger changes expected under higher emissions scenarios.
Key issues include:
Summer warming will mean more heat waves, reduced air quality, and increasing insect and waterborne diseases. Heat waves are projected to be more frequent, more severe, and longer lasting. The frequency of hot days and the length of the heat-wave season are both projected to be twice as great under a scenario of higher greenhouse gas emissions than a lower one. Ozone pollution tends to increase as temperatures rise, so air quality is likely to decline. Insects such as ticks and mosquitoes that carry disease are likely to survive winters more easily and produce larger populations in a warmer Midwest.
Reductions in Great Lakes water level could impact shipping, infrastructure, beaches, and ecosystems. Higher temperatures will mean more evaporation and hence a possible reduction in Great Lakes water levels, particularly in a scenario of higher greenhouse gas emissions. Reduced lake ice increases evaporation in winter, which could also contribute to a decline. A reduction would affect shipping, ecosystems, recreation, infrastructure, and dredging requirements. Costs will include lost recreation and tourism dollars and increased repair and maintenance costs.
More frequent flooding and, paradoxically, more water deficits are likely. The projected pattern of increasing precipitation in winter and spring and more frequent heavy downpours throughout the year is expected to lead to more frequent flooding. This puts people at risk of flood injury and waterborne disease. Heavy downpours can overload drainage systems and water treatment facilities, increasing the risk of waterborne diseases associated with sewage. Floods and higher temperatures can also damage other infrastructure, such as roads. In summer, with increasing evaporation and potentially longer periods between rainfalls, the likelihood of drought will increase. Water levels in rivers and wetlands are likely to decline as higher temperatures bring higher evaporation rates.
Increases in heat waves, floods, droughts, insects, and weeds will present challenges to managing crops, livestock, and forests. Although a longer growing season provides the potential for increased crop yields, spring flooding is likely to delay planting. An increase in disease-causing pathogens, insect pests, and weeds causes additional challenges for agriculture and forests. Livestock production is expected to become more costly as higher temperatures stress livestock, decreasing productivity and increasing costs associated with the needed ventilation and cooling equipment.
Native species are likely to face increasing threats from changing climate, pests, diseases, and invasive species. All major groups of animals including birds, mammals, amphibians, reptiles, and insects will be affected by climate change impacts on local populations and by competition from species moving into the Midwest from warmer regions. The potential for animals to shift their ranges to keep pace with the changing climate could be inhibited by major urban areas and the presence of the Great Lakes.
Adapted by Melanie Lenart, University of Arizona
Other Regional Climate Change Impacts from USGCRP: