Climate change is a global phenomenon with tangible effects that are increasingly observed in urban centers. Chicago, with its position on the Great Lakes and inland location, exhibits particular vulnerabilities to these shifts. The city’s unique geography shapes how global climate patterns translate into local impacts. These changes present distinct challenges for Chicago’s environment and its residents.
Shifting Temperature Patterns
Chicago’s temperature profile is undergoing alterations due to climate change, leading to warmer conditions across seasons. The city experienced its warmest year on record in 2024, with an average annual temperature of 55 degrees Fahrenheit, which is 3.8 degrees above normal. While high daytime temperatures have been typical, overnight low temperatures are also increasing. This trend contributes to a general warming.
The frequency and intensity of heat waves are increasing in Chicago. Projections suggest that severe heat waves could occur as frequently as every other year by the end of the century. By mid-century, the annual number of days over 95 degrees Fahrenheit is projected to increase from 2 to 18, with some areas experiencing up to 20 to 25 such days per year.
Winters in Chicago are becoming milder and shorter, with the season being the fastest-warming in the United States. Since 1970, Chicago’s winters have warmed an average of 3.2 degrees Fahrenheit. This warming means fewer extreme cold days and reduced snow cover. By mid-century, Chicago is projected to have 22 fewer days per year with minimum temperatures below 32 degrees Fahrenheit. These warmer winters can also lead to more dramatic freeze-and-thaw cycles.
Altered Precipitation and Water Levels
Chicago is experiencing a shift toward more intense and frequent heavy rainfall events. The heaviest rain events in the Great Lakes region have increased by 45% since 1958. Extreme rainfall events that once had a very low chance of occurring in a given year are becoming more common; The 2020s decade has already seen five extreme rainfall events in central Cook County, compared to two in the 2000s and 2010s. This increase in heavy downpours contributes to more frequent flooding and impacts the city’s water infrastructure.
Lake Michigan water levels are also subject to fluctuations, with the potential for both extreme highs and lows. Warmer temperatures can lead to increased evaporation, contributing to lower water levels. Conversely, periods of colder temperatures can result in reduced evaporation and greater ice cover, which can lead to higher water levels. For example, a rapid decline in lake evaporation due to colder winters in 2013-2014, followed by persistent above-average precipitation, led to record high levels in 2019-2020. These extreme swings in water levels pose challenges for the city’s infrastructure and coastal erosion.
Increased runoff from heavy rains can affect water quality in the Chicago River and Lake Michigan. More intense rainfall events are projected to increase combined sewer overflows into Lake Michigan by 50% to 120% by the end of the century. Such overflows can increase the likelihood of drinking water contamination.
Impacts on Urban Systems
Chicago’s built environment and essential services face stress from changing temperature and precipitation patterns. The city’s stormwater and sewer systems are vulnerable to being overwhelmed by intense rainfall. This can lead to basement flooding and combined sewer overflows. In July 2023, extreme rainfall caused widespread flooding of roadways and basements, with one event being among the costliest weather-related disasters in Cook County’s history.
Transportation networks in Chicago are also affected by these climate shifts. Flooding poses a threat, impacting roads, rail lines, and transit stations. Extreme heat can also damage infrastructure, leading to issues like rail buckling and signal equipment failures, causing service disruptions for public transportation.
Buildings and housing are impacted by increased energy costs for cooling due to hotter summers. Properties also face flood risks from heavy precipitation. The city’s density of asphalt and concrete contributes to an urban heat island effect, intensifying the dangers of heat waves, particularly in neighborhoods with less tree cover.
The energy grid experiences increased stress during extreme heat events because of higher demand for air conditioning. Prolonged heat events, defined as three or more days exceeding 90 degrees Fahrenheit, are projected to increase in the Chicago area. This places a greater burden on the electrical system.
Implications for Public Health and Ecosystems
Climate change presents threats to the health of Chicagoans. Increased heat-related illnesses and mortality are a concern, with projections suggesting that average heat-related deaths could quadruple by 2050. The 1995 heat wave in Chicago resulted in over 700 deaths. Higher temperatures can also worsen air quality, contributing to increased ground-level ozone and longer pollen seasons, which can exacerbate respiratory issues. Waterborne diseases are a potential risk from contaminated floodwaters, as increased runoff can expose people to pathogens. The mental health of residents can also be affected by the stress of extreme weather events and displacement.
The city’s local ecosystems are also undergoing changes. Warmer temperatures and altered precipitation patterns can affect urban wildlife and plant species. For instance, warmer winters can confuse amphibians and reptiles, causing them to emerge from hibernation too early, making them vulnerable to sudden cold snaps and predators. This can significantly reduce their populations.
Shifts in pest populations and the spread of invasive species are also linked to climate change. As temperatures rise, insect-borne diseases, such as West Nile virus, may become more prevalent. Native tree species in the Chicago region could decline, while non-native and invasive species might thrive as habitat suitability shifts. Invasive species can out-compete native plants for resources, harming the local ecology.