The deadliest extreme weather event is not what you think it is

LAS VEGAS — Extreme heat has already taken a deadly toll in the United States this summer, even as some of the hottest weeks are still to come.

The Northern Hemisphere is approaching the midway point of summer, and preliminary numbers from some of the country’s notorious hot spots show that heat has been a significant killer yet again this year.

Heat is sometimes called a “silent killer,” because its impact on the human body is not always obvious. Symptoms of heat-related illness — when the body’s organs lose the ability to regulate temperature and become dangerously overtaxed — often go unnoticed until it’s too late.

Nationally, extreme heat causes more deaths each year than any other weather event, including floods, hurricanes and tornadoes, according to the National Weather Service. Those risks are expected to increase in the years ahead, because climate change is increasing the frequency, intensity and duration of heat waves around the world.

This week, dangerously high temperatures are descending on the South, Midwest and Northeast, according to the NWS. Around 96 million people are under heat alerts Wednesday from New Orleans north to Minneapolis and spreading east through New England.

Meanwhile, in southern Nevada’s Clark County, the coroner’s office announced last week that 29 heat-related deaths have been reported so far this year — up from the same time in 2024. Clark County includes the city of Las Vegas, which is one of the fastest-warming cities in the country, according to a study published earlier this year by the nonprofit organization Climate Central.

The county recorded its first heat-related death for 2025 on May 9, weeks before its first confirmed heat-related fatality in late May 2024. Last year was particularly deadly for southern Nevada, with 527 heat-related fatalities, according to the Clark County Coroner and Medical Examiner’s office.

The summer of 2024 was southern Nevada’s hottest in recorded history, according to the National Weather Service. Las Vegas recorded a new record high temperature of 120 degrees Fahrenheit last July, and endured more than 100 days of triple digit temperatures.

Nearby, in Arizona’s Maricopa County, 15 heat-related deaths have been recorded as of July 19. That early figure trails the 23 confirmed deaths recorded by July 19, 2024, though public health records indicate that 299 deaths this year are still under investigation.

In May, the Maricopa County Department of Public Health said that last year, at least one heat-related death occurred every day in Maricopa County from June 18 to July 31.

In 2024, which was the hottest year on record for the county, authorities confirmed 602 heat-related fatalities, down from a record-shattering 645 heat-related deaths in 2023. That marked Maricopa's first decline in heat deaths in a decade.

Local officials launched several new initiatives aimed at keeping people cool and safe over the summer, including planting trees to increase shade in public spaces and resurfacing pavements with more reflective surfaces in certain areas to combat urban heat.

“For a lot of folks, heat is an inconvenience, but for others, it’s very much a matter of life and death,” said Ariel Choinard, a scientist at the Desert Research Institute in Las Vegas and head of the Nevada Heat Lab.

Certain people are more at risk than others, such as senior citizens, individuals with chronic health conditions or young children who may not be able to articulate how they are feeling, she said.

Exposure to extreme heat also tends to disproportionately affect lower-income communities, according to Choinard. While everyone in a city like Las Vegas is exposed to summertime high temperatures, how people experience that heat depends on if they have stable housing, whether they are dependent on public transportation, or if they have access to and can afford air conditioning.

A study published in August 2024 in the journal JAMA found that from 1999 to 2023, there were 21,518 heat-related deaths in the United States. The research tracked these deaths each year and found that heat-related mortality rates have increased over the past two decades, and particularly in the last seven years.

This year’s heat fatality numbers for Maricopa and Clark counties are considered preliminary, and not all counties or states have released early estimates of heat’s toll so far this year.

As such, early figures on heat deaths are a “lagging indicator,” Choinard said, because it takes time for the coroner’s office to carry out investigations and confirm whether or not heat was a factor in reported deaths. Final counts on heat-related mortality are often not released until the end of the year, or even early next year.

With weeks to go before temperatures cool off, extreme heat remains a threat across many states.

“Summer isn’t over, by any means,” Choinard said. “Here in Vegas, our heat season can stretch well into October.”

This article was originally published on NBCNews.com