Heat in the Heartland

The report finds that dangerously hot summer days and heat waves have become more common in the US Midwest since the 1940s and 1950s. It highlights that nighttime temperatures have risen, reducing the cooling relief necessary to prevent heat-related illness. The analysis, covering 10 cities, indicates that these trends are not solely due to urban heat island effects, as smaller cities showed similar increases. Future projections suggest a significant increase in days over 90°F and 100°F by the end of the century if high carbon emissions continue.

• Dangerously hot summer days and heat waves lasting three days or longer have increased in frequency across the Midwest over the last 60 years. In St. Louis, the average number of three-day heat waves per year rose from three in the 1940s to seven today.
• Summer nights have become hotter and more humid, which limits the relief from heat and increases health risks. In some cities, nighttime summer temperatures within certain air masses increased by 4° to 5°F over six decades.
• The increase in hot summer days is not exclusively caused by the urban heat island effect, as smaller cities in the study recorded similar increases to those seen in large cities.
• There has been a general decrease in the number of cool, dry days during the summer across all studied cities, reducing the available relief from heat.
• Under a higher-emissions scenario, the Midwest is projected to experience a sharp increase in days exceeding 90°F and 100°F by the end of the century. For example, in St. Louis, days over 100°F are projected to rise from fewer than 3 (1961–1990) to 43 (2070–2099).

APA

Union of Concerned Scientists (2012). Heat in the Heartland. https://www.ucs.org/sites/default/files/2019-09/Heat-in-the-Heartland-Executive-Summary.pdf

Chicago

Union of Concerned Scientists. Heat in the Heartland. 2012. https://www.ucs.org/sites/default/files/2019-09/Heat-in-the-Heartland-Executive-Summary.pdf.

Wikipedia

{{cite report |author=Union of Concerned Scientists |title=Heat in the Heartland |date=July 2012 |url=https://www.ucs.org/sites/default/files/2019-09/Heat-in-the-Heartland-Executive-Summary.pdf |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{unionofconcernedscientists2012heat, author = {{Union of Concerned Scientists}}, title = {{Heat in the Heartland}}, institution = {Union of Concerned Scientists}, year = {2012}, month = jul, url = {https://www.ucs.org/sites/default/files/2019-09/Heat-in-the-Heartland-Executive-Summary.pdf}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }