Skip to main content
Governor JB Pritzker Illinois.gov Contact IDNR DNR A to Z

Changing Temperatures

How much warmer?

Globally, temperatures are increasing at a fast rate. As the figure below shows, average surface temperatures in most parts of the world are between 0.5° and 2.0° Celsius higher (0.9° and 3.6° Fahrenheit) than they were 50 years ago. In fact, global temperatures in June and July 2023 were the warmest on record.

Figure 1: Average surface air temperatures 2011-21 compared to 1956-76. NASA's Scientific Visualization Studio. https://data.giss.nasa.gov/gistemp/maps/index_v4.html

In Illinois, average annual temperatures are also increasing. Between 1895 and 2019, Illinois’ statewide annual average temperature increased 1.2° Fahrenheit (0.67° Celsius). Half of that warming occurred in the last 30 years (NOAA NCEI, 2020).

While a temperature increase of 1-2 degrees may seem small, even small changes have large impacts. Most scientists agree that we should limit global warming to 1.5o Celsius (2.7o Fahrenheit) to minimize the devastating impacts of climate change on our environment. This is the goal set by the Paris Agreement, which Illinois joined in 2019 as part of the US Climate Alliance, and the United States rejoined in 2021. This agreement has been ratified by all but three countries.

Will there be more extreme heat events?

Climate change is causing more extreme heat events. Extreme heat events can trigger heat stroke, which can lead to death.  Heat is the leading weather-related cause of death in the US. Small children, older people, people with chronic diseases, low-income populations, and outdoor workers are all at risk.

Many animals and plants will be threatened by higher temperatures, too. High temperatures also cause water to evaporate faster, leading to drought and wildfires.

If we do not take steps to reduce global warming, Illinois will likely see more and more very hot days, as shown in the figure below. We can limit the increase in very hot days by lowering global emissions (see the “lower emissions” scenario, the two maps on top). This will require that Illinois join nations around the world to reduce greenhouse emissions. Without global climate action, we can expect to see many more hot days, as shown in the two “higher emissions” scenarios, the two maps on the bottom. 

Figure 2: Changes in Annual Number of Very Hot Days (95 degrees F or Higher). Wuebbles et al., 2021)