These American cities are warming the most

CNN
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No, it’s not your imagination: American summers really are getting hotter and longer.

Human-caused climate change is accelerating heat across the country, but it’s most intense in cities, home to more than 260 million Americans. That’s because buildings, roads and sidewalks radiate more heat than grass and trees, in what’s known as the urban heat island effect, which can increase urban temperatures by as much as 20 degrees Fahrenheit.

The country’s 50 most populous cities have gotten warmer over the past 50 years, with all but three experiencing more “extremely hot” days above 95 degrees, according to an analysis of data from the International Institute for Environment and Development, shared exclusively with CNN.

These are the cities that are on the front line.

This year’s summer has been marked by record temperatures, power outages and train delays due to overheated tracks. deformed and threatened to derail. In one Arizona county, hundreds of people are believed to have died from heat-related causes. Phoenix paramedics are now traveling with body bags filled with ice to submerge people suffering from heat exhaustion or heat stroke.

If you take the 50 largest cities in the country and add up the number of days with temperatures above 95 degrees, there have been at least 1,071 this summer, 161 more than the average for the past decade. for the same period.

Those days aren’t evenly distributed across cities. Las Vegas and Phoenix, for example, have seen more than 80 days with temperatures above 95 degrees this summer, while coastal California cities like Los Angeles and San Francisco have been spared entirely.

Washington, D.C., and Baltimore are experiencing their hottest summers in at least a decade. Each has recorded at least 18 extremely hot days this year. Last summer, they recorded just three and five, respectively, through the end of July.

As for cities that have seen the biggest increase in days with temperatures above 95 degrees, Las Vegas takes the top spot. It’s been a very hot summer, with 83 days (18 more than its average over the past decade) and every day in July in the city was above 105 degrees, reaching a high of 120.

San Antonio, Texas, experienced 54 extremely hot days, 16 more than its 2013-2023 average, while Nashville, Tennessee, recorded 23, also 16 days above average.

Over the past five decades, the number of days of extreme heat has increased from 1,064 to 1,857 among the 50 most populous cities, an increase from an average of 21 days per city to 37.

“The overall trend is clear: major U.S. cities have seen a significant increase in the number of extremely hot days,” said Tucker Landesman, a senior researcher at the International Institute for Environment and Development.

More days of extreme heat and temperatures rising by a few degrees may seem manageable, but even small increases, especially when combined with increased humidity, can increase the risk of serious health emergencies, such as heat exhaustion and even heat stroke, which can be fatal.

And these impacts are having a disproportionate impact on vulnerable groups.

“Recent years have shown that heat is a killer, and this may be particularly true for children, the elderly and people with lower incomes or living in substandard housing,” Landesman told CNN. “High temperatures are also linked to premature births, stillbirths, and other health problems during pregnancy.”

Over the long term, large cities in Texas, Arizona and inland California have been hardest hit in terms of the increase in extremely hot days.

Of the 10 cities that recorded the largest increase since the mid-1970s, seven are in Texas.

In 1976, San Antonio experienced one week of extreme heat, but by 2023 that had increased to nearly 13 weeks, an increase of 1,276%.

Austin went from less than three weeks to more than 12, while Houston went from just over a week to more than seven.

Beyond climate change, parts of Texas have become more vulnerable to extreme heat over the past five decades because their cities have expanded rapidly and their downtowns have become denser. And populations there continue to grow rapidly: By 2023, San Antonio added 22,000 people to its population, more than any other city, followed by Fort Worth, which added more than 21,000.

In Austin, city officials aim to cover 50 percent of the city with trees by 2050 to prevent some of the city’s heat from being trapped in concrete and asphalt.

“Too often, heat is talked about as if it were just ‘the weather,’ but we have built our cities to be heat islands, often much warmer than the surrounding land, exacerbating the effects of climate change,” Landesman said. “This effect can be especially acute in low-income areas that lack quality green space.”

Outside of Texas, but also among the top 10 cities with the largest increase in extremely hot days, are Tucson, Arizona, which went from 79 days to 132, as well as Fresno, California, from 60 to 92, and Denver, Colorado, from just five days to 31, representing a jump from one workweek of extreme heat to six full weeks.

Of the 50 cities, only three (Los Angeles, Omaha and Kansas City) did not experience an increase in extremely hot days over the five-decade period.

Arizonans living in urban centers are accustomed to extreme desert heat, but like much of the country, they, too, are having to adjust to even longer periods of heat.

Phoenix, Mesa and Tucson are the places with the most days of extreme heat. In 2023, Phoenix averaged 158 days, three weeks longer than 50 years ago and 40% of the year.

Tucson’s increase was the largest in Arizona, with 53 more days of extreme heat, or seven more weeks.

If you are one of those people who thinks that summer doesn’t start until a really hot day comes, then summers start earlier and end later.

In the decade from 1974 to 1983, the first extremely hot day of the season, on average, occurred on June 22 and the last on September 4. But in the past decade, that period begins more than a week earlier and lasts about a week longer than it used to.

So if you lived in those earlier decades, summers may seem to be getting longer.

As the heat becomes deadly, there is growing awareness of the importance of adapting to a warmer world to avoid reaching temperatures that challenge human survival, while reducing fossil fuel pollution as much as possible.

Landesman suggests that cities expand green space, increase shade, provide public cooling stations and improve messaging about the dangers of heat to prevent serious human health consequences and costs.

“As the wealthiest country in the world, the United States has the resources and technology to address extreme heat,” Landesman said.

“We can’t fix this problem by installing air conditioning; in fact, that would only make it worse, because the United States gets much of its electricity by burning fossil fuels. It would also be prohibitively expensive for the most vulnerable, and cities should be livable for everyone, not just the rich.”