Summer 2021 was one of Ohio’s hottest on record, especially at night

Climate Columbus

Warmer-than-average summer nights push temperature records

cleveland indians tigers progressive field summer night

A sunset over Progressive Field in the sixth inning during game one of a doubleheader between the Detroit Tigers and the Cleveland Indians on June 30, 2021 in Cleveland, Ohio. (Photo by Ron Schwane/Getty Images)

COLUMBUS (WCMH) – This summer was a scorcher around Ohio, but not just during the heat of the day.

Cities across the Buckeye State saw temperatures in June through August – meteorological summer – break or nearly break records that go back well over a century, according to weather station data tracked by the National Oceanic and Atmospheric Administration.

Much of the record-breaking was in northern Ohio, where cities from Cleveland to Findlay saw some of their hottest average summer temperatures in history. Mansfield, for example, saw its hottest summer ever, dating 101 years.

Northern Ohio cityWarmest summer rankYears of recordkeeping
Mansfield1st101 years
Toledo2nd149 years
AkronT-3rd127 years
Findlay4th79 years
ClevelandT-14th150 years
YoungstownT-17th93 years
WarrenT-50th126 years
Source: NOAA. For cities with multiple weather stations, station with longest history chosen.

“The unusually high average temperatures reflect warmer nights and higher humidity more than hot days,” said NBC4 meteorologist Ben Gelber.

Ohio cities farther south fared a bit cooler because they saw less sunshine, Gelber said. Columbus, for example, saw its 19th-warmest summer in 143 years of recordkeeping.

Columbus had 20 days this summer where the temperature hit or exceeded 90 degrees, slightly above normal for June through August, which Gelber said “reflect many nights when morning readings didn’t drop below the low 70s.”

Those hot overnight periods trace back to the second week of June, he said, culminating in a heat wave that lasted from Aug. 18 to the closing days of the month with the arrival of Hurricane Ida’s remnants.

Nights warm as climate warms, threatening comfort and health

Overnight temperatures in June, July and August also made a stark impact on Ohio’s record books. Four major cities – Toledo, Akron, Mansfield and Findlay – broke their records for average minimum summer temperature.

CityAvg. min. summer temp. rank (2021)Years of recordkeeping
Toledo1st149 years
Akron1st127 years
Mansfield1st101 years
Findlay1st79 years
Dayton4th128 years
Zanesville4th75 years
ColumbusT-7th143 years
YoungstownT-12th93 years
ClevelandT-15th150 years
WarrenT-20th126 years
CincinnatiT-30th150 years
Source: NOAA. For cities with multiple weather stations, station with longest history chosen.

In Mansfield, which also set an average overall summer temperature record, low temperatures were 4.2 degrees higher than normal.

Nighttime temperatures in Ohio are trending higher as Earth warms due to climate change, caused by humans emitting heat-trapping gases like carbon dioxide. Since 1970, the average minimum summer temperature in Columbus has risen more than 4 degrees, according to a 2019 analysis by the nonprofit research group Climate Central.

Climate Central warm summer nights 2019
(Graphic via Climate Central)

Columbus saw the highest increase among the 10 cities Climate Central analyzed, coming out just ahead of Cleveland’s 4.2-degree increase.

“When we have more moisture in the air or higher humidity, nights cool off more slowly,” said Gelber, who also teaches meteorology at The Ohio State University. “So, instead of low temperatures falling into the more typical 60s, we are seeing an increasing number of nights where temperatures don’t drop below 70 degrees in central and northern Ohio.”

Columbus had 29 nights this summer that did not get below 70 degrees, tied for the 4th-most in 142 years of recordkeeping at John Glenn International Airport. The capital city’s average low temperature was 65.8 degrees this summer, 2.2 degrees above normal.

Warmer nights force us to use more energy by running fans and air conditioning, increasing greenhouse gas emissions tied to the power grid. But there are also health effects, even beyond it being harder to fall asleep on muggier nights.

“The concern is that higher humidity puts more stress on our bodies,” Gelber said, “because it’s difficult to cool off when the moisture in the air is high.”

Hotter nights, then, pose a heightened threat to vulnerable people like the elderly and people with underlying health conditions. But geographically, nights are worse in cities.

“Pavement and buildings retain heat, so nighttime cooling is already limited in urban areas,” Gelber said. This is called the heat island effect, which a Climate Central study this summer found adds an average of 6 degrees to Columbus’ temperature, compared to nearby rural areas.

“When the humidity is consistently higher because of more moisture in the air – which has been a trend since the mid-20th century in our portion of the country – nights tend to be that much warmer,” Gelber said. “And especially in urban settings, that adds to our heat stress.”

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