Heat in the Heartland: 60 Years of Warming in the Midwest (2012)

July 2012
Report shows the growing health risks of heat waves and hot summer weather in the Midwest.

Rising temperatures are not just a concern for the future. Dangerously hot weather is already occurring more frequently in the Midwest than it did 60 years ago.

The report, Heat in the Heartland: 60 Years of Warming in the Midwest, presents an original analysis of weather data for five major urban areas — Chicago, Cincinnati, Detroit, Minneapolis, and St. Louis — as well as five smaller nearby cities.

The results from the analysis are clear: Hot summer weather and heat waves have been increasing in cities in the nation’s heartland over the last six decades on average. The report documents this trend, explores its health implications, and looks at what the largest cities are doing to adapt to these changes and protect their residents.

It is the third report in a UCS series on Climate Change and Your Health.

Heat creates serious health risks

High temperatures can lead to dehydration, heat exhaustion, and deadly heat stroke. Very hot weather can also aggravate existing medical conditions such as diabetes, respiratory disease, kidney disease, and heart disease.

Urban populations, the elderly, children, and people with impaired health and limited mobility are particularly susceptible to heat-related illness and death.

Dangerously hot weather is increasing in the Midwest

Download individual city fact sheets (PDFs):

Chicago | Cincinnati | Detroit | Minneapolis | St. Louis

The report looked at changes in summertime weather patterns using information dating back to the 1940s and 1950s.

The study focused on weather systems called air masses — vast bodies of air overhead that define the weather around us. Specifically, it explored how dangerously hot summer air masses and cool, dry summer air masses have changed in frequency over the last 60 years.

The report also examined how the average daytime temperatures, humidity levels, and nighttime temperatures within different types of weather systems have changed over time.

Key findings include:

  • Heat waves lasting three days or more have become more common over the last six decades. St. Louis has approximately four more three-day heat waves each year than it did in the 1940s.
  • On average, hot humid days have increased more rapidly in frequency, while hot dry days have increased in temperature more rapidly across the Midwest since the 1940s and 1950s.
  • The meteorological characteristics of these weather types are also changing. In general, hot air masses have become hotter and more humid during nighttime hours.
  • In some cities, average nighttime temperatures within some air mass types have increased as much as 4 to 5 degrees Fahrenheit (˚F) over the six decades.
  • Relief from heat is harder to find—all of the cities studied now have fewer cool, dry days in the summer.
  • The results aren’t due solely to an urban heat island effect on major cities. Less urban neighboring locations showed similar increases in hot summer air masses.

Where do we go from here? It's up to you.

The goal of this report was to understand how summer weather has changed in the Midwest, and how this can inform our efforts to minimize the health risks projected with future climate change.

The report did not examine how these weather changes are linked to climate change, though its findings are consistent with other studies that examine the links between human behavior and a warming world.

Each of the larger cities mentioned in the report is taking its own steps to protect public health and save lives during extreme heat events. For more specific information on city action plans and resources, please see the individual fact sheets above.

As individuals, we can address climate change by implementing practical policies and programs and changing our own behaviors. The choices we make today about the way we live and the energy we use will make a difference for the health and well-being of ourselves, our children, and our descendants long into the future.