Summer Temperatures On The Climb

Locations across the U.S. are reporting an increase in the number of extremely hot days over the last 51 years.
Madison has seen an increase of 2.3 degrees in summer temperatures.
Madison has seen an increase of 2.3 degrees in summer temperatures.(WMTV)
Published: Jul. 7, 2021 at 10:23 PM CDT
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MADISON, Wis. (WMTV) -June was one of the hottest on record in the Madison area with July starting off on a very similar note. This is part of a larger trend of summers getting hotter thanks to climate change. As heat-trapping greenhouse gases increase the global average temperature, we are experiencing higher average temperatures and more extreme and record-breaking heat events. This is most apparent in the summertime since it’s the hottest time of the year.

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Our partners at Climate Central evaluated 51 years of summer temperature data in 246 U.S. locations. Results show an overall warming trend for the summer season. About 95% (233) of the locations had an increase in their average summer temperature, with 50% (122) of those increasing by 2°F or more. Nine out of the top ten fastest-warming summer locations were located in the Western U.S. and Texas, with Reno, Nev. (10.6°F),  Las Vegas (5.6°F), and El Paso, TX (5.5°F) in the lead. Madison has experienced a 2.3 degree warming in it’s average temperature since 1970.

A look at regions of the country and the change in average summer temperature since 1970.
A look at regions of the country and the change in average summer temperature since 1970.(WMTV)

The exception though, has been across the northern Plains, where average temperatures have been holding steady. That’s most likely due to transpiration from the expanding corn crop. Corn “sweats” lots of water vapor into the air, which is helping to counterbalance the increase in summer heat compared to the rest of the country. However, you shouldn’t think they’re getting off easy out there, because summer heat indices (feel-like temperatures) across the Corn Belt are often brutal.

Summer night temperatures increased by 2°F or more in 61% of the locations. In Madison, there has been a dramatic increase in overnight lows. Since 1970, this has increased by 5.2 degrees! The primary culprit is an increase in humidity. That’s from both the Gulf of Mexico, and to a lesser degree, that large corn crop to our west.

Overnight temperature change in the summer since 1970.
Overnight temperature change in the summer since 1970.(WMTV)

It was also noted that 38% of locations reported, on average, at least one additional week of extremely hot temperatures annually (compared to 1970) and 59% have reported an annual increase of at least three days. The largest change is in Miami with 79 additional days above a sizzling 90°F. Oddly enough, Madison has seen a decrease in 90 degree temperatures. Since 1970, 8 fewer 90 degree days are occurring each summer on average. The increase in humidity is helping to mitigate the number of days we get into the 90s. As a reminder, that’s not considering the heat index, which is reaching new heights thanks to more muggy air than ever before.

Average 90 degree days have decreased in Madison.
Average 90 degree days have decreased in Madison.(WMTV)

Extreme heat is the deadliest kind of hazardous weather to humans and has many negative consequences to human health. Extreme heat can increase heat-related illnesses in vulnerable populations. This includes seniors, younger children, and people without air conditioning. Summer heat can contribute to poor air quality by trapping harmful pollutants close to the Earth’s surface and creating ground-level ozone. These pollutants can inflate respiratory problems in people with asthma and other lung diseases. In areas without air conditioning, warmer nights can cause health issues by not letting our bodies cool off and recover after intense heat events. One study also reveals that warmer nights can disrupt our sleeping patterns. Cities can get much hotter than surrounding suburban and rural areas because they have more heat-absorbing surfaces and materials. Studies have found that this “urban heat island” effect disproportionately affects Black and immigrant communities, which typically have less shade-covering trees than whiter areas.


Summer (June, July, and August) temperature data from 1970-2020 were obtained from the Applied Climate Information System. Displayed trend lines are based on a mathematical linear regression. Climate Central’s local analyses include 247 stations. However, for data summaries based on linear trends, only 246 stations are included due to large data gaps in Wheeling, W. Va.

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