Summers Are Getting Warmer Nationwide, Including in Milwaukee

Summers have been heating up across the country and Wisconsin is no exception, according to a new analysis from the group Climate Central.

The group analyzed data from the National Oceanic and Atmospheric Administration. The analysis found 97 percent of 242 cities studied are seeing hotter summers with an average temperature increase of 2.6 degrees Fahrenheit since 1970.

Shel Winkley, meteorologist for Climate Central, said nearly one-third of those cities have warmed by 3 degrees or more, including the city of Milwaukee.

“When you look at the states across the U.S, summer is warming, which means that it is starting earlier. It’s eating into our spring season, and it’s lasting longer,” Winkley said.

Meteorological summer starts in June, and extreme heat has already descended on southern portions of the country. Temperatures are forecasted to lean above normal this summer in Wisconsin.

Winkley said climate change is making heat waves more frequent and longer. The last two years have been the hottest on record. Despite that data, the Trump administration has rolled back efforts to address climate change in favor of more oil and gas production.

In Milwaukee, Climate Central found that the city has warmed 3.4 degrees in the last 55 years, adding about 17 more days that have been hotter than normal.

“Effectively, what we’ve done by adding carbon pollution into our atmosphere, by putting this wool blanket around the Earth, is that we’ve added over half a month of extra above-average heat days in the city of Milwaukee,” Winkley said.

Milwaukee also suffers from the urban heat island effect, in which more developed areas absorb and retain more heat.

Other Wisconsin cities like Wausau, Green Bay, Madison, La Crosse and Eau Claire have seen temperatures increase between 1.6 to 2.8 degrees during the same timeframe. They’ve experienced around 10 to 16 more days hotter than normal.

Wisconsin counties have seen temperatures rise from a low of 0.4 degrees in Pierce County to a high of 2.5 degrees in Jackson County. Winkley said the data shows that the north-central portion of the state is seeing the most warming.

The analysis is largely in line with the findings of Wisconsin’s Initiative on Climate Change Impacts, according to Jonathan Patz, a professor in the Nelson Institute for Environmental Studies and Population Health Sciences at the University of Wisconsin-Madison.

He noted the latest report found temperatures in Wisconsin have increased by around 3 degrees since the 1950s.

“We’re seeing more nighttime warming than daytime warming, which is a problem for health,” Patz said. “Because if you don’t have cooling temperatures in the nighttime, it’s more dangerous, and there are more people at risk from heat waves.”

State Climatologist Steve Vavrus agreed the state has seen a trend of more extreme nighttime heat in the summer.

“For instance, nighttime temperatures not falling below 70 degrees,” Vavrus said. “When it’s really sticky and difficult to sleep, if you don’t have air conditioning, those kind of nights have become more common in Wisconsin in the last few decades.”

Vavrus noted that the state hasn’t seen an increase in really high daytime temperatures above 90 or 100 degrees. He said Wisconsin has largely escaped more extreme heat during the day compared to other parts of the country. He said that may be due to the state growing wetter during the summer, as well as more intense agriculture pumping moisture into the atmosphere.

Even so, the number of days hotter than 90 degrees is likely to triple in Wisconsin by mid-century. Milwaukee could see three times as many days with a heat index above 105 degrees by 2050.

Hotter summer temperatures can prompt more heat-related illnesses and worsen air quality, according to Dr. Elizabeth White, a family medicine physician in rural southwestern Wisconsin. She said outdoor workers are more vulnerable to illnesses like heat exhaustion or heat stroke.

“Our construction workers are at higher risk for negative health impacts of that direct heat,” White said. “We also see that there are other groups of individuals that are more vulnerable to these direct heat-related illnesses.”

She said those include people suffering from mental health disorders, heart disease or diabetes. She added that young children and pregnant women are also more at risk of severe illness. Another Climate Central analysis found that extremely hot days increased the risk of preterm birth by more than one-third in cities like Green Bay, Madison and Milwaukee.

White urged communities to think about identifying spaces with clean water, food and air conditioning that are open 24/7 during times of extreme heat.

Extreme heat kills more people nationwide than any other weather event. A record 2,325 people died from extreme heat in 2023.

Listen to the WPR report

Analysis finds summers are heating up nationwide, including in Wisconsin was originally published by Wisconsin Public Radio.