Summer is hotter than it was a generation ago, and for people living and working in five U.S. cities, that shift has been dramatic. A May 2026 analysis by Climate Central examined average summer temperatures across 243 major U.S. cities between 1970 and 2025. Summers have warmed in 97% of them. Across those cities, the average increase is 2.6 degrees, and cities now see 22 more hotter-than-normal days per summer than they did in the 1970s.
Five cities stand out from the rest.
The 5 Fastest-Warming U.S. Cities This Summer
Reno, Nevada tops the list by a wide margin, with average summer temperatures up 11.3 degrees Fahrenheit since 1970. Boise, Idaho and El Paso, Texas both follow at +6.3 degrees. Las Vegas, Nevada sits at +6.2 degrees, and Salt Lake City, Utah rounds out the top five at +6.0 degrees.
Reno's increase is close to double that of the next city on the list. To put that in terms Shandas used when speaking to Newsweek: a 6-to-11-degree increase in average summer temperatures is like moving the climate of a city hundreds of miles south toward the equator.
Why the West Is Warming Fastest
Vivek Shandas, a professor of geography at Portland State University, described what is happening to these cities as a "double exposure." Inland western cities have absorbed faster warming than most of the country over the past 50 years, with no coastal moderation from the Pacific Ocean to soften the impact.
Urban growth compounds the problem. Reno and Boise both grew fast after 1970. Farmland and open space gave way to roads, parking lots, and buildings. The land that once shed heat through shade and evaporation is gone, and the temperature records reflect that trade.
Climate Central found that human-caused climate change was the leading driver of summer warming in 221 of the 243 cities analyzed, 91%.
What a 6-to-11 Degree Rise Produces
Shandas described that range as "an extreme outlier" from a public health perspective. The increase does not feel like a modest uniform bump. It shifts the entire range of summer conditions upward. Days that used to reach 90 degrees now push past 100. Heat waves last longer. A heat event that used to be unusual is now a normal summer week.
Hot nights drive the most serious health outcomes. When temperatures stay elevated after dark, the body has less time to recover from daytime heat exposure, and that's when heat illness, hospitalization, and death rates climb. Climate Central reports that extreme heat is the leading cause of weather-related deaths in the United States, according to its analysis of federal mortality data.
Shandas also flagged indoor overheating as a growing concern, in parts of the inland West and Pacific Northwest where homes were built for cooler conditions and may lack air conditioning or adequate ventilation.
The burden falls hardest on neighborhoods with less tree cover, more pavement, older housing stock, and fewer resources. Those areas face both the highest temperatures and the greatest health risk.
Cold Water Is Part of the Answer
Hydration under heat stress is not a wellness habit. It is a physiological requirement. You lose water faster when you are hot, and dehydration accelerates the risk of heat illness. Cold water helps lower core body temperature faster than warm water and people drink more of it, which means the people on your team stay functional longer on a 105-degree afternoon in El Paso or a humid August day in a Las Vegas warehouse.
A cooler that delivers ice-cold water on demand is not optional equipment for facilities in these cities. It is a basic operational necessity.
How Bottleless Nation Coolers With Ice Help
Bottleless Nation's water and ice coolers connect to your building's water line, filter the water, and deliver it cold, on demand, without plastic jugs, delivery schedules, or the ongoing cost of keeping cases of bottled water in stock. The ice-equipped models keep water cold enough to matter and run through August without problems.
We operate across 55+ markets nationwide, including cities across the West and Southwest where this summer is going to demand the most from your team and your facility. If your current setup is a warm jug cooler or a case of plastic bottles, this summer is the right time to upgrade.
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Data: Climate Central, "Summer Warming Trends Across U.S. Cities," May 2026. Expert commentary sourced from Newsweek, June 2026.