Climate-fueled heat wave isn’t done with Wisconsin

Clark Evans, a meteorological professor at UW-Milwaukee, is impressed by the severity of the recent heat waves that have crept northward, part of a global trend of blistering temperatures. “Some of our hottest days here in Wisconsin tend to have relatively low humidity, relatively low dew points,” Evans told Wisconsin Examiner. “So it’s hot, but it doesn’t feel as muggy or as oppressive. Whereas this event is both hot with temperatures over 100 degrees – or at least one day if not two in some locations – but it’s also very humid with dew point temperatures in the 70s, and humidity values in the 70-80% range as well.” That’s a potent combination and it “can create a lot of stress on one’s body. It becomes  much more difficult to cool off when you get hot.”

Conditions like those that swept the state in August and continued over Labor Day weekend  heighten the possibility of heat-related injuries and deaths. As temperatures climbed just in time for the Republican debate in Milwaukee last month, local schools shut down for multiple days due to the heat. Labor Day temperatures climbed to near 100 degrees, according to the National Weather Service. Last week, the Department of Natural Resources (DNR) issued a warning for high fire danger in southern and central Wisconsin. Wildfire activity has been on the rise this year, burning more acres than in previous years due to drought.

Wildfires burned in four central Wisconsin counties on the first day of September. The largest fire scorched five acres before it was controlled. Meanwhile, a staggering 4 million people statewide are enduring drought conditions, with a 0.8% increase since last week. The drought conditions were unique in their own right, since normally a drought means dry ground without a lot of humidity. “But here, as I was mentioning, we had both the hot air and the high humidity,” said Evans. “So the drought didn’t really seem to have that much of an impact for this specific event. But generally, when it’s dryer it tends to be hotter, and vice versa.”

For some, these are signs of an ever worsening climate crisis. Jeff Goodell, the author of “The Heat Will Kill You First” stressed that point in a recent interview with Wisconsin Public Radio. “There’s a strong case to be made that people who live in northern cities are more at risk from these freakish and increasingly hot weather patterns that are going to be emerging in the future,” said Goodell. “Wisconsin is not known, of course, as a place where you’ve experienced a lot of extreme heat waves…But it is now in this new climate, a place where I would not be surprised to see temperatures far beyond what you’re used to at some point in the not-so-distant future.” Around the globe – including in Europe and Asia,  heat domes defined the summer months of 2023.

As the heat wave simmered into late August, word of a new method of modeling future climate conditions emerged. The concept, known as ensemble boosting, uses computer modeling to simulate large data sets of extreme – yet plausible – heat wave predictions. Evans says new models make the relationship between these weather events and climate change clearer.

In 2021 a report by the Wisconsin Initiative on Climate Change Impacts (WICCI) also predicted that extremely hot days in the state would become more common. The report noted that Wisconsin is likely to trend towards wetter conditions, particularly during the winter, spring and fall. Extreme rain and precipitation events are also likely to increase in frequency.

For many local towns and cities, the effects may be startling. The WICCI report found, for example, that Green Bay can expect the number of days that exceed 90 degrees to increase from about seven days per year to up to 20. “These changes in average temperature will increase the frequency and magnitude of many extreme weather events,” the report states. “By mid-century extreme heat days over 90 degrees Fahrenheit in Wisconsin will likely triple. The number of hot nights when the temperature does not drop below 70 degrees Fahrenheit will likely quadruple.”

Evans says demand for public services like cooling stations will become more crucial. “But then beyond that, you start to get to bigger, more ‘how do we define our cities and communities?’ types of questions,” said Evans. “Do we need more green space? Should we mitigate sprawl and build upward, recognizing that if you condense buildings, you create a really intense heat effect in those cities, but you lessen the spread of that heat effect spatially within the broader community? So there are a lot of trade-offs that go into that type of question beyond, ‘How do I handle the things that are happening right now?’”

Different communities may also have different climate adaptive needs. A recent DNR study found that in Milwaukee, temperature affects some communities more than others. “They demonstrated that in some of the most disadvantaged zip codes in Milwaukee is actually where you have this strongest heat effect where it’s anywhere from eight to 10 degrees warmer than the surrounding areas,” said Evans.

When TV news and radio stations broadcast a recorded high temperature for Milwaukee, some of the city’s most vulnerable communities may in fact be even hotter. “When you get a temperature reading like, Milwaukee’s high was 101 degrees that one day last week, that’s at the airport over an open field,” Evans explains. “Whereas in the city, the urban heat island was actually likely warmer on the level of 105-112 degrees because of that urban heat island effect. And so, when it’s hot, it’s even hotter inside of our cities. And in Milwaukee in particular, that tends to be inside of the more disadvantaged portions of town as well as the downtown more. So from a societal impact perspective, that has a disproportionate negative effect on people who have the least amount of resources to be able to do something about it.”