Extreme heat is the deadliest weather phenomenon in the United States. It's also one of the easiest to underestimate: We feel it on our skin, or perhaps see it shimmering in the air around us, but it doesn't announce itself with the destructive aplomb of a hurricane or wildfire. Still, heat waves are becoming practically synonymous with summer.
Climate change is only making heat waves worse. They're getting more frequent, up from an average of two per year in the United States in the 1960s to six per year in the 2010s and '20s. They're also about a day longer than they were in the ‘60s, and they're more intense; those two factors combined, in particular, make them more deadly. This year's expected El Niño will bring even more heat with it: NOAA's summer outlook for the United States, shown below, paints a swath of above-average temperatures across much of the country.
NOAA's seasonal temperature outlook for the summer of 2023.National Oceanic and Atmospheric Administration
I’ve spent a lot of time thinking about how to cover heat waves. Each is unique — suffering of any kind is always unique, even if the broad strokes are not — yet the things one can say about them are, for the most part, largely the same. Records will break, power grids will strain, and people will be hurt: This is the reality of climate change.
So this year, we are trying an experiment: We will document particularly notable heat waves around the world as they happen, but rather than devote separate stories to them, each heat wave will get a short entry within this larger page. We will call out especially vivid details or statistics and include links to local outlets that can provide more information to anyone looking for it.
The goal here is to create a record of the very real impact of climate change today. By the end of the summer, this page will likely be filled with entry after entry showcasing the ways heat affected people around the world over the course of a few months. This is, I am aware, potentially fertile ground for climate anxiety, but our hope is that the project can help us recognize how our lives are changing and allow us to refocus on what we can do to adapt to our new reality.
Each entry has its own URL. If you wish to share details of any particular heat wave, simply scroll to that entry and hit the share button on your phone or copy the link in your browser. If you'd like to share this tracker as a whole, scroll back up to this introduction. This timeline will be in reverse chronological order, or in other words the newest events will appear at the top of the page.
This project is publishing in the midst of a heat wave hitting multiple Asian countries, and we’ve also included a couple of heat waves that have already come and gone; as the summer progresses, you'll see updates from the entire Heatmap staff and the gradual shaping of a larger story of heat. Again, this is an experiment, and we'd love to hear what you think about it — if you have strong thoughts one way or another, please send them to neel [at] heatmap [dot] news. —Neel Dhanesha
The UN confirms this was the hottest summer ever
September 6: As we near the end of the summer — though ambient temperatures this week may suggest otherwise — the World Meteorological Organization (WMO) has announced that Earth just had its hottest three-month period on record, and the year so far is the second-warmest after 2016, which saw an extreme El Niño.
“Climate breakdown has begun,” said UN Secretary-General António Guterres in a statement. “Leaders must turn up the heat now for climate solutions. We can still avoid the worst of climate chaos — and we don’t have a moment to lose.”
According to the Copernicus Climate Change Service, August is estimated to have been around 1.5°C warmer than the preindustrial average. Last month saw the highest global average sea surface temperatures on record, at 20.98°C, and Antarctic sea ice was at a record low for that point in the year. Those sea surface temperatures will have a significant impact on hurricane season; as we saw with Idalia, extremely high ocean temperatures can supercharge tropical storms.
These numbers are no surprise — scientists have, of course, been warning of these catastrophic impacts for years — and this report is just the latest in a long line of UN reports that catalog the ways our planet is changing. The question, as always, is if this report will spur any more action than the previous ones did, or whether it will amount to yet another howl lost in the wind. —Neel Dhanesha
Texas gets a reprieve from wicked heat
August 23-28: On Thursday, record-breaking heat tied the hottest temperature ever recorded in Houston at 109 degrees. In Dallas on Friday, highs climbed into the high 100s. And in Austin on Sunday, the temperature climbed up to 109 degrees. From Thursday to Sunday, the Electricity Reliability Council of Texas issued a conservation request every day — asking Texans to lower their energy use as air conditioners blasted.
Texans will get a relative reprieve from the heat over the coming days: Dallas won’t cross back over the triple-digit mark until Saturday, while Houston won’t get hotter than 100 degrees this week. Still, temperatures remain high — a reminder that just because summer break is over in many places, summer weather isn’t, making air conditioning in schools and on buses more critical than ever. —Will Kubzansky
Large heat dome bakes the Corn Belt
August 22: The Midwest joins the South and Southwest this week in pulling the short straw of weather forecasts. The National Weather Service projects a large heat dome will “persist in at least 22 states until the end of the week,” Axios reports, affecting 143 million Americans. Numerous cities are experiencing heat indexes between 110 and 115 degrees Fahrenheit; Lawrence, Kansas, even reached a “feels-like” temperature of 134 on Sunday.
Not only will the extreme highs endanger lives, the heat waves might threaten “a bumper U.S. harvest that’s key to keeping global inflation in check,” Bloomberg reports. The United States expects to reap its second largest corn harvest on record this year, but the upcoming heat might dry out fields that are already showing signs of being parched.
Over the weekend, relief for the Midwest will come from cooler winds flowing down from Canada, AccuWeather reports. Unfortunately, the welcome breeze might also come along with “bouts of poor air quality” and smoke from Canadian wildfires. —Annie Xia
The Pacific Northwest is extremely hot again
August 16: With triple-digit highs, the Pacific Northwest has joined the ranks of states breaking heat records this summer. Portland, Oregon, hit 108 degrees Fahrenheit on Monday, a record for the month of August. Seattle, Washington, also set a new daily record on Monday when it reached 96 degrees.
Combined with strong winds and moderate to severe drought levels, high temperatures in the region also mean heightened wildfire risk. Almost 3,000 firefighters are already “battling the seven large fires burning across Oregon and Washington,” CNN reports.
The sweltering temperatures continue a streak of oppressive summers in the Pacific Northwest. Dr. Steven Mitchell, medical director of a Seattle hospital’s emergency department, told The New York Times that “he couldn’t remember treating a single case of severe heat illness or heat stroke” before 2021, when a deadly heat wave struck the region. —Annie Xia
Humidity is boiling the Gulf Coast
August 7: In places like New Orleans, the old adage applies: It’s not just the heat, it’s the humidity. The high is set to hover between 100 and 97 through Friday, but the heat index will sit between 116 and 111. Louisiana, like much of the country, is seeing an unusually hot summer: Baton Rouge experienced its warmest month on record in July. All the while, central Mississippi is experiencing highs between the high 90s and low 100s, with heat indices reaching 120 degrees, according to the National Weather Service’s outpost in Jackson.
The heat killed 16 Louisianans in June and July. And given that extreme heat causes the worst impacts for people experiencing poverty and creates particularly devastating effects for Black Americans, it’s worth noting that Mississippi and Louisiana have the two highest poverty rates in the country as well as the highest proportion of Black residents of any two states. —Will Kubzansky
Iran shuts down over the heat
August 2: Iran is shutting down. The New York Times reports that government agencies, banks, schools, soccer leagues are all closed Wednesday and Thursday, allegedly due to the heat, which is expected to reach 104 degrees Fahrenheit in Tehran. In Ahvaz, a southwestern city, the high on Wednesday is a blistering 123 degrees.
Per the Times, some Iranians have expressed doubts about the alleged reason for the shutdown — instead claiming that the country’s electric grid can’t meet demand. All the while, Iran faces extensive water shortages across the country, largely due to mismanagement of its resources. —Will Kubzansky
South Korea and Japan place populations on high heat alerts
August 2: A deadly heat wave is striking both sides of the Sea of Japan.
In South Korea, two deaths were reported on Tuesday due to high heat — they were senior citizens working outside — bringing the death toll from the heat wave to 12. With temperatures above 100 degrees Fahrenheit in Yeoju, a city south of Seoul, the country has raised its warning system for heat to the highest level, the first instance since 2019.
And in Japan, a 13-year-old girl and an elderly couple died due to heat-related causes on Friday. Temperatures have climbed above 103 degrees this week in parts of the country, and 32 prefectures are under the government’s “special heatstroke alert,” according to The Washington Post.
Japan is coming off a brutal month of July, which included the longest run of 95 degree temperatures in Tokyo since records began in 1875. Heat waves are especially devastating for Japan, which has one of the world’s oldest populations. —Will Kubzansky
Phoenix to cool down to ... 106 degrees
July 28: No American city has been more emblematic of this summer’s relentless heat than Phoenix, where the temperature has climbed above 110 degrees Fahrenheit for 29 consecutive days. That streak looks like it might finally come to a close, with highs ranging from 106 to 109 from Monday to Wednesday next week as the forecast calls for rain over the weekend. But by Thursday, the mercury will climb above 110 yet again.
With the heat showing no signs of truly relenting, Arizona Democrats have proposed a novel solution — calling on President Joe Biden to issue a presidential disaster declaration for extreme heat, unlocking the Federal Emergency Management Agency’s response capabilities. And all the while, more than 30 wildfires are blazing across the state of Arizona. —Will Kubzansky
The heat reaches the Midwest and Northeast
July 26: For most of the summer, stories about extreme heat in the U.S. have been limited to the South and Southwest. That’s changed in the last few days, as heat is forecast to scorch the Midwest and Northeast this week. On Thursday, New York will see highs in the mid-90s and D.C. up to 99 — both with heat indexes in the mid-100s. In Kansas City, highs will sit in the 100s through Friday and climb back up into the triple digits again on Monday; Indianapolis will reach 99 degrees Friday.
Late July is an appropriate time for heat waves — and this burst does not look like a lengthy one, with the 10-day forecast dipping back into the 80s — but it’s also worth noting that cities like D.C. are less prepared for extreme heat than Miami or Phoenix. D.C. has entered a hot weather emergency, but in New York, some advocates have cautioned that the city is not ready for the challenges ahead. —Will Kubzansky
Yes, the heat waves are being driven by climate change
July 25: The summer has offered a deluge of heat headlines — scrolling through this page is the proof. But zooming out, the context matters: Has this summer’s heat been uniquely driven by climate change? The answer is almost certainly yes, according to a study from researchers at Imperial College London, the Royal Netherlands Meteorological Institute, and the Red Cross Red Crescent Climate Centre.
The flash study is not peer-reviewed — it moved too quickly to go through that process — but it notes that “without human-induced climate change these heat events would … have been extremely rare.” The high temperatures in North America and Europe, it adds, would have been “virtually impossible” without climate change. Heat waves may have still occurred, but the key is the intensity: In the U.S., Europe, and China, climate change accounted for between 1 to 2.5 degrees Celsius (1.8 to 4.5 degrees Fahrenheit) of additional heat. —Will Kubzansky
The heat keeps breaking records in the Southwest
July 17: Records are falling left and right in the Southwest. At 118 degrees Fahrenheit, Phoenix broke its all time high temperature record on Saturday. The city is also approaching breaking its record for the most 110 degree days in a row. In El Paso, the temperature at the airport has hit 100 degrees for 32 consecutive days, the longest streak ever. And according to The New York Times, the National Weather Service called for 45 record highs across the U.S. last weekend.
And as wildfires burn in Southern California, the heat wave is showing no signs of letting up. Phoenix will see highs in the 110s through Monday, as will Las Vegas. At this point, the heat wave has been classified as another heat dome, and Texas is feeling the brunt of it too, with San Antonio and Austin under excessive heat warnings. The heat wave is most dangerous for vulnerable members of society, especially people who are homeless and seniors — placing an outsized and crucial burden on cooling centers in the Southwest. —Will Kubzansky
Death Valley Predicted to Tie Hottest Temperature on Earth
Grant Faint/Image Bank via Getty Images
July 12: In a summer full of record-breaking heat, the fact that it’s hot in Death Valley is almost comforting. On Sunday, the national park in the Mojave Desert, known for being the hottest place on Earth, is projected by the National Weather Service to reach 130 degrees Fahrenheit, which would probably tie the record for the world’s highest temperature. The uncertainty stems from some controversy surrounding the record: While the valley was said to have reached temperatures of 134 degrees in 1913, experts have questioned the legitimacy of that reading. That leaves 130 degree days in 2020 and 2021 as the hottest temperatures on record — in Death Valley or anywhere.
While Death Valley’s heat is something of a novelty, it has catastrophic impacts elsewhere. Las Vegas’s high will only be 12 degrees cooler (118 degrees), and temperatures will reach 106 degrees on the same day in San Bernardino. —Will Kubzansky
Brutal heat stretches on in the Southwest
July 10: After 10 days with high temperatures above 110 degrees, the highs in Phoenix are forecasted to eclipse that mark for at least the next nine days. According to the National Weather Service’s Phoenix office, the record for consecutive 110-degree days is 18; the office is placing the probability that the record gets shattered at 50%. And like Texas’ heat dome earlier this summer, evening temperatures aren’t declining as substantially as they usually do, leaving Arizonans without relief.
In New Mexico, the National Weather Service office out of Albuquerque is describing the week ahead as “near-record heat.” And temperatures in Las Vegas, Nevada, are set to get even more brutal over the course of the week, with the high going from 107 degrees on Monday to a forecasted high of 117 on Sunday. The heat will also lead to brutal temperatures in Death Valley — potentially up to 127 degrees on Sunday — according to the The Washington Post. —Will Kubzansky
Texas and the South swelter
July 10: Texas can’t catch a break this summer — and the South is catching yet another heat wave as well. Heat indexes in Dallas, Houston, New Orleans, and Miami are set to reach 107 to 108 degrees this week. Water temperatures around South Florida are well above average, and the chance that rain breaks the heat in the area is limited over the next few days. This year is already the hottest on record in Miami, according to WLRN. —Will Kubzansky
The Southwest braces for ‘some of the worst’ heat waves in its history
July 7: Phoenix and Tuscon are under excessive heat warnings for at least the next six days. Afternoon highs are projected to reach between 105 and 115 degrees Fahrenheit — Friday will get up to 112 degrees in Phoenix — bringing temperatures above average for early July, according to AZCentral.
It might last well into the month. According to the National Weather System’s warning: “We are still anticipating this current heat wave to continue through next week and likely beyond with it rivaling some of the worst heat waves this area has ever seen.” A big heat wave also brings pressure to the electric grid, particularly in heavily populated areas like Phoenix, as residents crank up their ACs. One study from earlier this year showed that a five-day heat wave and blackout would combine to send more than 50% of the city’s population to the emergency room.
It’s also not just Arizona that will catch the worst of this wave: New Mexico, Las Vegas and Death Valley all have scorching temperatures in store over the next week, The Washington Post notes. —Will Kubzansky
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Beijing, Taiwan see scorching temperatures
July 6: Outdoor work came to a halt in Beijing as temperatures reached 104 degrees Thursday in the Chinese capital. A heat wave is gripping parts of China, including the capital and the nearby Henan province. Before 2023, Beijing had experienced temperatures above 104 degrees six times, CNN reported. This year alone, the temperature has eclipsed that mark on five days. In Taiwan, temperatures are set to reach 104 degrees Saturday, according to the country’s Central Weather Bureau. All the while, flooding has also led to devastation in China, causing 15 deaths in Chongqing, Hunan province, and elsewhere. —Will Kubzansky
Southern California broils under a ‘routine’ heat wave
June 30 - July 5: In the Antelope Valley and Santa Clarita Valley, temperatures reached 105 and 101 degrees respectively Monday, the Los Angeles Times reported. David Gomberg, an NWS forecaster, told the Times that high heat is to be expected in Southern California around now — to some extent, the weather is “routine,” he said.
Still, temperatures climbed rapidly in the Los Angeles area beginning Friday, especially inland and in the desert. And because the rise came so suddenly following a temperate period, it may have posed an unusually high risk to Californians who hadn’t yet acclimated to the season’s hotter temperatures. Extreme heat can also create arid conditions begetting wildfires, though no reports of serious fires in California have emerged following July 4 fireworks displays. —Will Kubzansky
The Texas heat dome just won’t budge
July 5: This year’s Fourth of July was the world’s hottest day on record, and that record will likely be broken again this summer. In Texas, the heat was nothing new: The last day El Paso recorded a high temperature under 100 degrees was June 15. Since then, every day has gotten up to the triple digits — with the heat reaching 108 degrees on June 26 and 27.
In other words, it’s still really, really hot in Texas as a heat dome remains firmly planted over the state. Some parts of Texas have seen a handful of cooler days — July 4 wasn’t quite as brutal in Houston, for instance, and San Antonio’s temperatures have largely fallen back into the ‘90s. But the southern part of the state is in what the San Antonio Express-News describes as a “rut”: Heat is giving way to marginally cooler temperatures but the weather is expected to get hotter and more humid again.
For older people or people who work outdoors, the sustained heat has proven especially deadly. The vast majority of Texas’s prisoners, meanwhile, are without air conditioning. —Will Kubzansky
The North Atlantic Ocean is boiling hot
The North Atlantic Ocean is in the middle of a startling heat wave that could have far-reaching repercussions.
The weeks-long marine heat wave broke records for the months of May and is expected to do the same in June. Sea surface temperatures around the U.K. and northern Europe are an astonishing 9 degrees Fahrenheit above average in places, The Washington Post reports.
“Totally unprecedented,” Richard Unsworth, a biosciences professor at the U.K.’s Swansea University, told CNN. It’s “way beyond the worst-case predictions for the changing climate of the region.” Scientists say the warming oceans could have significant consequences, from harming marine life to decreasing the sea’s capacity to absorb pollution.
Above-average heat has also hit the U.K. Temperatures are expected to hit 89 degrees Fahrenheit in southeast England over the weekend.
As a flotilla in the Atlantic searched for the missing Titan submersible, the prominent environmental writer Bill McKibben tweeted, “The truly terrifying news this week is not what happened deep beneath the sea, it’s what’s going on at the surface.” —Annie Xia
The Texas heat wave dips — but doesn’t end
June 22: Texans will only get a brief reprieve from the most extreme highs of their heat wave before temperatures pick back up early next week. Notably, temperatures aren’t falling considerably at night, making the heat even more dangerous. North Texas will see the mercury rise up to 104 degrees through Thursday, with the small caveat that humidity will decline into a more comfortable range as the week goes on. In parts of Southwest Texas, the heat won’t let up at all: the high temperatures in Del Rio will hover between 107 and 110 through next Wednesday.
The Electric Reliability Council of Texas issued its first voluntary conservation notice of the heat wave this past Tuesday. While the utility was able to meet demand, it requested that all Texans, especially government agencies, reduce their electricity use.
Mexico is similarly seeing scorching temperatures, which have led to eight deaths already. And high heat in the Rio Grande Valley means that migrants who traverse the border in Southwest Texas could be left exposed to the same high heat, which can have deadly consequences. —Will Kubzansky
Over a hundred dead in India amid 115-degree heat
Week of June 19: Temperatures in the northern Indian states of Uttar Pradesh and Bihar, two of the most populous in the country, reached as high as 115 degrees Fahrenheit (46 degrees Celsius), CNN reports. The extreme heat triggered power cuts, leaving people without running water, fans, or air conditioners.
The Associated Press reports nearly 170 people had died as of June 20, overwhelming hospitals, morgues, and crematoria — although state officials dispute the connection to the heat wave. Nearly half of the deaths came from a single district, Ballia, in Uttar Pradesh; officials say they have opened an investigation into the cause, which they say could be linked to contaminated water. Members of opposition parties blame the state government and its chief minister, Yogi Adityanath, for not investing enough in medical facilities or warning residents about the heat wave ahead of time. —Neel Dhanesha
Texas’ blistering heat wave is not letting up
June 19: The numbers from Texas’ heat wave are already striking: Dallas tied a humidity record on Thursday, and tens of millions of Texans woke up Friday to heat advisories or warnings. Temperatures will approach — and possibly break — records in Austin early next week, with highs between 104 and 106 through Wednesday. In the area, the heat indices will be highest over the Rio Grande plains and coastal plains, according to the National Weather Service’s Austin/San Antonio office.
Houston, in the meantime, saw its first excessive heat warning since 2016, with heat indices potentially breaking 115 degrees Friday and Saturday. Texas’ grid has held up (so far) — though the Electric Reliability Council of Texas has projected that next week will shatter the record levels of electricity demand that were just set this week, thanks to the number of air conditioners expected to be on full blast. —Will Kubzansky
Texas — and its grid — braces for skyrocketing temperatures
June 14: Triple-digit heat has arrived early in Texas. Large parts of central and southeast Texas saw the heat index climb into the 100s Wednesday, topping out in McAllen at a searing 118. The heat wave is expected to spread and last through the week, hitting San Antonio, Dallas, Houston, and Austin, where it will feel like 112 degrees Thursday.
But while meteorologists watch for record heat and humidity, others will keep their eye on the state’s isolated electricity grid. Its operators, the Electric Reliability Council of Texas, warned of record-breaking electricity use Friday, an ominous signal for a state that has struggled with deadly blackouts in recent years. But this is just Texas’s first test of the summer: The grid operators noted that the record-breaking demand will likely be surpassed later in the summer. —Will Kubzansky
Puerto Rico’s heat index hits 125
June 7-11: As skies over New York and Washington, D.C., turned orange from wildfire smoke, Puerto Rico and nearby Caribbean nations sweltered under a heat dome. The Heat Index, which takes into account both heat and humidity, went as high as 125 degrees in parts of Puerto Rico — a number that Jeff Berardelli, chief meteorologist at Tampa Bay’s WFLA-TV, said was astonishing. Temperature records broke across the island.
The Puerto Rican power grid still hasn’t recovered after Hurricane Maria hit the island in 2017, and over 100,000 Puerto Ricans reportedly lost power (though, as Pearl Marvell pointed out in Yale Climate Connections, the exact number cannot be verified because the island’s power company asked PowerOutage.us, which tracks outages, to stop collecting data on Puerto Rico until it can “replace their technology and provide more accurate data”). As I wrote in May, the combination of extreme heat and blackouts has the potential to be incredibly deadly, though no deaths were reported from this heat dome as of publication. —Neel Dhanesha
Little respite for Asia
June 5: Large parts of China have seen record-breaking heat over the past month, one year after the worst heat wave and drought in decades hit the country. This year, Yunnan and Sichuan provinces saw temperatures exceed 40° C (104° F); according to CNN, heat in some parts of the country was so bad that pigs and rabbits died on farms and carp being raised in rice fields "burned to death" as water temperatures rose. Henan province had the opposite problem; extreme rain flooded wheat fields there, ruining crops in the country's largest wheat-growing region.
Meanwhile, a prolonged heat wave in Vietnam is keeping temperatures between 26 and 38 degrees Celsius (78.8 and 100.4° F), prompting officials to turn off street lights and ask citizens to cut down on their power consumption to avoid blackouts. VNExpress reports that many Vietnamese citizens who can't afford air conditioners are seeking respite in public spaces like libraries, buses, department stores, and cafes. —Neel Dhanesha
An early-season heat wave in the Pacific Northwest
May 12: Some 12 million people in Washington and Oregon were under a heat advisory for four days starting May 12 as temperatures in the region topped out at more than 20 degrees above the normal high at that time of year, which should have been in the mid-60s.
"It’s harder for people in the Pacific Northwest to cool down when it’s 90 out than for people in, say, Phoenix or Las Vegas — cities that were constructed with heat in mind," wrote Heatmap Founding Staff Writer and Washington native Jeva Lange in her larger story about this heat wave. "Seattle, for example, is the second-least-air-conditioned metro area in the country (behind only “the coldest winter I ever spent was a summer in” San Francisco). Just over half of the homes in the area have a/c, and many of them are new buildings." —Neel Dhanesha and Jeva Lange
Asia swelters, breaking seasonal records
April: A large, deadly heat wave baked much of Asia for two weeks in April, Axios reported. Parts of India saw temperatures beyond 40°C (104°F), while temperatures in Thailand reached their highest levels ever, breaking past 45°C (113°F) for the first time in that country's history. Thirteen people died in Mumbai, and hundreds of people across the Asian continent were hospitalized. —Neel Dhanesha
This article was first published on June 5, 2023. It was last updated on September 6, 2023, at 3:59 PM ET.
More about heat and how the world is coping:
1. The Deadly Mystery of Indoor Heat
2. Don’t Be Too Chill About Your Air Conditioning Dependency
3. America Is Depending on Renewables This Summer
4. Dermatologists Have Bad News to Share About Climate Change
5. April Heat Waves Brought May Infernos
NOAA's seasonal temperature outlook for the summer of 2023.National Oceanic and Atmospheric Administration
EPA Administrator Lee Zeldin. Kevin Lamarque-Pool/Getty Images 
Courtesy of United States Forest Service