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By Alice Gibbs
Senior Reporter
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A new analysis of U.S. temperature data has identified five cities where summer heat has increased the most over the past half-century, with one western city far above the rest.
Reno, Nevada, has seen average summer temperatures rise by 11.3 degrees Fahrenheit since 1970, according to research published May 20 by Climate Central. It is followed by Boise, Idaho, and El Paso, Texas (both +6.3 degrees), Las Vegas, Nevada (+6.2) and Salt Lake City, Utah (+6.0).
The findings are based on an analysis of 243 major U.S. cities examining changes in average temperatures across June, July and August between 1970 and 2025, with Climate Central finding that summers have warmed in 97 percent of the cities studied.
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Why These Cities Are Heating Up Faster
The cities at the top of the ranking are concentrated in the West and Southwest—regions already known for hot, dry summers but now are experiencing sharper warming. Climate Central found that summer warming has been strongest, on average, across the Northwest, Southwest and South.
Reno stands out as a clear outlier, with nearly double the increase seen in the next-highest cities.
Vivek Shandas, a professor of geography at Portland State University, said inland western cities such as Reno and Boise are facing what he called a “double exposure”: broader climate warming across the region combined with rapid urban development that intensifies how heat is felt locally.
“The western United States has experienced some of the most rapid warming in North America over the past several decades,” Shandas told Newsweek. “These effects are often amplified in interior continental locations that lack the moderating influence of the Pacific Ocean.”
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He said fast-growing cities in arid and semi-arid parts of the country are especially vulnerable.
“Many cities such as Reno and Boise have grown rapidly since the 1970s," he said. "Expansion of roads, parking lots, commercial areas and residential development has replaced natural landscapes and agricultural lands that previously provided cooling through shade and evaporation. As a result, temperature increases can be more pronounced than in wetter regions.”
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As these cities, and most others across the U.S., have seen rises in summer temperatures over the last few decades, Shandas said the cause was clear.
“The best available evidence suggests that climate change is responsible for most of the long-term increase in average summer temperatures,” he said.
Climate Central’s analysis also attempts to isolate the role of human-caused climate change, which was the leading driver of summer warming in 221 of the 243 cities analyzed, or about 91 percent.
How Much Hotter Summers Have Become
While the headline figures highlight the fastest-warming cities, the broader dataset shows that most U.S. cities have experienced rising summer temperatures since 1970. Across the 236 cities where warming was observed, average summer temperatures increased by 2.6 degrees.
Major metro areas such as New York City have also warmed, though less drastically—by around 1.2 degrees over the same period. Climate Central also found that nearly every city studied now experiences more hotter-than-normal summer days than in the early 1970s—22 more, on average.
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What 6- to 11-degree Rise Means for Residents
A rise of even a few degrees in average summer temperature can have outsized impacts on daily life, particularly during heatwaves.
Shandas said that a rise of roughly 6-11 degrees in average summer temperatures is “extraordinarily large” from a public health perspective because it shifts the entire range of summer conditions toward more dangerous heat.
Rather than feeling like a small uniform increase, he said, it means more days above 90 and 100 degrees, longer heat waves, hotter nights, earlier extreme heat and greater strain on homes and power systems.
“Perhaps most importantly, temperatures that were once considered rare become commonplace,” he said. “A 6- to 11-degree increase in average summer temperatures is like moving the climate of a city hundreds of miles south towards the equator.”
That has serious implications for residents of these cities because hot nights are often one of the strongest predictors of severe health outcomes.
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“Once temperatures cross certain thresholds, which differs depending on an individual's sensitivities, the likelihood of heat-related illness, hospitalization and death rises rapidly,” Shandas said.
When temperatures stay elevated after sunset, the body has less chance to recover from daytime heat, raising the risk of heat-related illness, hospitalization and even death. Climate Central notes that extreme heat is the leading cause of weather-related deaths in the United States.
Indoor overheating is another growing concern, particularly in parts of the inland West and Pacific Northwest where many homes were built for historically cooler climates and may lack air conditioning or adequate ventilation.
“This infrastructure is especially concerning for older adults, renters, low-income households, people with chronic illnesses and residents in manufactured homes, mobile home parks and multifamily apartments,” Shandas said.
Beyond health impacts, hotter summers can drive up electricity demand and household cooling costs while putting roads, rail, power and water systems under greater stress.
Shandas also warned that the burden is not shared equally. Neighborhoods with fewer trees, more pavement, older housing and fewer resources often face the highest temperatures and the greatest health risks.
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