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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
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
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
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
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
August 9-11: Florida is often synonymous with heat, but the heat index in Tampa Bay climbed up to 112 degrees on Wednesday — flirting with 113, the mark at which an excessive heat warning is issued. The Tampa Bay Times reported that the warning issued Wednesday was possibly the area’s first excessive heat warning ever, with the caveat that records might be faulty.
While the heat has let up slightly, a heat advisory remains in effect from Fort Myers up to Chiefland, and the area has exceeded its electricity demand records twice this week. On Friday, the heat index at Tampa International Airport reached 110 degrees, and values are expected to climb up to 108 on Saturday, according to the National Weather Service. —Will Kubzansky
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
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
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
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
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
July 26: Devastating consequences of the climate crisis are playing out in Algeria, Greece, Italy, and Tunisia, as wildfires spread and take dozens of lives — more than 40 in total and 34 in Algeria alone. The wildfires are being driven in part by intense heat, up to 119.7 degrees Fahrenheit in Algeria and 120 degrees in Tunisia. While those temperatures have cooled slightly, they will reach up to 111 degrees in Tunis come Friday and already climbed into the triple digits in Greece on Wednesday. Meanwhile, Greek authorities have evacuated more than 20,000 people from Rhodes, a popular vacation spot. —Will Kubzansky
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
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
July 14: A year after Europe saw 60,000 excess deaths due to heat waves, according to a study published by the scientific journal Nature Medicine, Southern Europe is scorching again. In Greece, the Acropolis closed midday Friday to tourists with high temperatures in Athens expected to reach 104 degrees. Parts of Spain saw temperatures going up to 113 degrees Monday, and another heat wave is expected to arrive Sunday. Italy, in the meantime, is expecting that next week could break the record for the highest temperatures ever recorded on the continent.
Europe has taken a new approach to heat waves — giving them names like hurricanes in an effort to raise awareness about their severity, an idea my colleague Neel Dhanesha wrote about last year. The first round of heat this week was dubbed Cerberus; the second round set to arrive this weekend is named Charon. —Will Kubzansky
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
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
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
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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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
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
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 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
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
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
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
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
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
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
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
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
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Here at Heatmap, we write a lot about decarbonization — that is, the process of transitioning the global economy away from fossil fuels and toward long-term sustainable technologies for generating energy. What we don’t usually write about is what those technologies actually do. Sure, solar panels convert energy from the sun into electricity — but how, exactly? Why do wind turbines have to be that tall? What’s the difference between carbon capture, carbon offsets, and carbon removal, and why does it matter?
So today, we’re bringing you Climate 101, a primer on some of the key technologies of the energy transition. In this series, we’ll cover everything from what makes silicon a perfect material for solar panels (and computer chips), to what’s going on inside a lithium-ion battery, to the difference between advanced and enhanced geothermal.
There’s something here for everyone, whether you’re already an industry expert or merely climate curious. For instance, did you know that contemporary 17th century readers might have understood Don Quixote’s famous “tilting at windmills” to be an expression of NIMYBism? I sure didn’t! But I do now that I’ve read Jeva Lange’s 101 guide to wind energy.
That said, I’d like to extend an especial welcome to those who’ve come here feeling lost in the climate conversation and looking for a way to make sense of it. All of us at Heatmap have been there at some point or another, and we know how confusing — even scary — it can be. The constant drumbeat of news about heatwaves and floods and net-zero this and parts per million that is a lot to take in. We hope this information will help you start to see the bigger picture — because the sooner you do, the sooner you can join the transition, yourself.
Without further ado, here’s your Climate 101 syllabus:
Once you feel ready to go deeper, here are some more Heatmap stories to check out:
The basics on the world’s fastest-growing source of renewable energy.
Solar power is already the backbone of the energy transition. But while the basic technology has been around for decades, in more recent years, installations have proceeded at a record pace. In the United States, solar capacity has grown at an average annual rate of 28% over the past decade. Over a longer timeline, the growth is even more extraordinary — from an stalled capacity base of under 1 gigawatt with virtually no utility-scale solar in 2010, to over 60 gigawatts of utility-scale solar in 2020, and almost 175 gigawatts today. Solar is the fastest-growing source of renewable energy in both the U.S. and the world.
There are some drawbacks to solar, of course. The sun, famously, does not always shine, nor does it illuminate all places on Earth to an equal extent. Placing solar where it’s sunniest can sometimes mean more expense and complexity to connect to the grid. But combined with batteries — especially as energy storage systems develop beyond the four hours of storage offered by existing lithium-ion technology — solar power could be the core of a decarbonized grid.
Solar power can be thought of as a kind of cousin of the semiconductors that power all digital technology. As Princeton energy systems professor and Heatmap contributor Jesse Jenkins has explained, certain materials allow for electrons to flow more easily between molecules, carrying an electrical charge. On one end of the spectrum are your classic conductors, like copper, which are used in transmission lines; on the other end are insulators, like rubber, which limit electrical charges.
In between on that spectrum are semiconductors, which require some amount of energy to be used as a conductor. In the computing context these are used to make transistors, and in the energy context they’re used to make — you guessed it — solar panels.
In a solar panel, the semiconductor material absorbs heat and light from the sun, allowing electrons to flow. The best materials for solar panels, explained Jenkins, have just the right properties so that when they absorb light, all of that energy is used to get the electrons flowing and not turned into wasteful heat. Silicon fits the bill.
When you layer silicon with other materials, you can force the electrons to flow in a single direction consistently; add on a conductive material to siphon off those subatomic particles, and voilà, you’ve got direct current. Combine a bunch of these layers, and you’ve got a photovoltaic panel.
Globally, solar generation capacity stood at over 2,100 terawatt-hours in 2024, according to Our World in Data and the Energy Institute, growing by more than a quarter from the previous year. A huge portion of that growth has been in China, which has almost half of the world’s total installed solar capacity. Installations there have grown at around 40% per year in the past decade.
Solar is still a relatively small share of total electricity generation, however, let alone all energy usage, which includes sectors like transportation and industry. Solar is the sixth largest producer of electricity in the world, behind coal, gas, hydropower, nuclear power, and wind. It’s the fourth largest non-carbon-emitting generation source and the third largest renewable power source, after wind and hydropower.
Solar has taken off in the United States, too, where utility-scale installations make up almost 4% of all electricity generated.
While that doesn’t seem like much, overall growth in generation has been tremendous. In 2024, solar hit just over 300 terawatt-hours of generation in the U.S., compared to about 240 terawatt-hours in 2023 and just under 30 in 2014.
Looking forward, there’s even more solar installation planned. Developers plan to add some 63 gigawatts of capacity to the grid this year, following an additional 30 gigawatts in 2024, making up just over half of the total planned capacity additions, according to Energy information Administration.
Solar is cheap compared to other energy sources, and especially other renewable sources. The world has a lot of practice dealing with silicon at industrial scale, and China especially has rapidly advanced manufacturing processes for photovoltaic cells. Once the solar panel is manufactured, it’s relatively simple to install compared to a wind turbine. And compared to a gas- or coal-fired power plant, the fuel is free.
From 1975 to 2022, solar module costs fell from over $100 per watt to below $0.50, according to Our World In Data. From 2012 to 2022 alone, costs fell by about 90%, and have fallen by “around 20% every time the global cumulative capacity doubles,” writes OWID analyst Hannah Ritchie. Much of the decline in cost has been attributed to “Wright’s Law,” which says that unit costs fall as production increases.
While construction costs have flat-lined or slightly increased recently due to supply chain issues and overall inflation, the overall trend is one of cost declines, with solar construction costs declining from around $3,700 per kilowatt-hour in 2013, to around $1,600 in 2023.
There are solar panels at extreme latitudes — Alaska, for instance, has seen solar growth in the past few years. But there are obvious challenges with the low amount of sunlight for large stretches of the year. At higher latitudes, irradiance, a measure of how much power is transmitted from the sun to a specific area, is lower (although that also varies based on climate and elevation). Then there are also more day-to-day issues, such as the effect of snow and ice on panels, which can cause issues in turning sunlight into power (they literally block the panel from the sun). High latitudes can see wild swings in solar generation: In Tromso, in northern Norway, solar generation in summer months can be three times as high as the annual average, with a stretch of literally zero production in December and January.
While many Nordic countries have been leaders in decarbonizing their electricity grids, they tend not to rely on solar in that project. In Sweden, nuclear and hydropower are its largest non-carbon-emitting fuel sources for electricity; in Norway, electricity comes almost exclusively from hydropower.
There has been some kind of policy support for solar power since 1978, when the Energy Tax Act provided tax credits for solar power investment. Since then, the investment tax credit has been the workhorse of American solar policy. The tax credit as it was first established was worth 10% of the system’s upfront cost “for business energy property and equipment using energy resources other than oil or natural gas,” according to the Congressional Research Service.
But above that baseline consistency has been a fair amount of higher-level turmoil, especially recently. The Energy Policy Act of 2005 kicked up the value of that credit to 30% through 2007; Congress kept extending that timeline, with the ITC eventually scheduled to come down to 10% for utility-scale and zero for residential projects by 2024.
Then came the 2022 Inflation Reduction Act, which re-instituted the 30% investment tax credit, with bonuses for domestic manufacturing and installing solar in designated “energy communities,” which were supposed to be areas traditionally economically dependent on fossil fuels. The tax then transitioned into a “technology neutral” investment tax credit that applied across non-carbon-emitting energy sources, including solar, beginning in 2024.
This year, Congress overhauled the tax incentives for solar (and wind) yet again. Under the One Big Beautiful Bill Act, signed in July, solar projects have to start construction by July 2026, or complete construction by the end of 2027 to qualify for the tax credit. The Internal Revenue Service later tightened up its definition of what it means for a project to start construction, emphasizing continuing actual physical construction activities as opposed to upfront expenditures, which could imperil future solar development.
At the same time, the Trump administration is applying a vise to renewables projects on public lands and for which the federal government plays a role in permitting. Renewable industry trade groups have said that the highest levels of the Department of Interior are obstructing permitting for solar projects on public lands, which are now subject to a much closer level of review than non-renewable energy projects.
Massachusetts Institute of Technology Researchers attributed the falling cost of solar this century to “scale economies.” Much of this scale has been achieved in China, which dominates the market for solar panel production, especially for export, even though much of the technology was developed in the United States.
At this point, however, the cost of an actual solar system is increasingly made up of “soft costs” like labor and permitting, at least in the United States. According to data from the National Renewables Energy Laboratory, a utility-scale system costs $1.20 per watt, of which soft costs make up a third, $0.40. Ten years ago, a utility-scale system cost $2.90 per watt, of which soft costs was $1.20, or less than half.
Beyond working to make existing technology even cheaper, there are other materials-based advances that promise higher efficiency for solar panels.
The most prominent is “perovskite,” the name for a group of compounds with similar structures that absorb certain frequencies of light particularly well and, when stacked with silicon, can enable more output for a given amount of solar radiation. Perovskite cells have seen measured efficiencies upwards of 34% when combined with silicon, whereas typical solar cells top out around 20%.
The issue with perovskite is that it’s not particularly durable, partially due to weaker chemical bonds within the layers of the cell. It’s also more expensive than existing solar, although much of that comes down inefficient manufacturing processes. If those problems can be solved, perovskite could promise more output for the same level of soft costs as silicon-based solar panels.
The country’s largest source of renewable energy has a long history.
Was Don Quixote a NIMBY?
Miguel de Cervantes’ hero admittedly wasn’t tilting at turbines in 1605, but for some of his contemporary readers in 17th-century Spain, windmills for grinding wheat into flour were viewed as a “dangerous new technology,” author Simon Winchester writes in his forthcoming book, The Breath of the Gods: The History and Future of the Wind. One interpretation of Cervantes’ novel might be that Quixote was “actually doing battle with progress.”
Nearly four and a half centuries later, harnessing the energy of the wind remains controversial, even if the breeze is one of humankind’s longest-utilized resources. While wind is the largest source of renewable electricity generation in the United States today, high construction costs and local opposition have more recently stymied the industry’s continued expansion. The new presidential administration — suspicious of wind’s reliability and place in the American energy mix — has also been doing its very best to stunt any future growth in the sector.
Whether you’re catching up on Trump’s latest regulatory moves, you have your own concerns about the safety of the technology, or this is your first time even thinking about this energy resource, here is the blow-by-blow — sorry! — on wind power in the U.S.
At their most basic conceptual level, wind turbines work by converting kinetic energy — the energy of an object in motion; in this case, air particles — into electrical energy that can be used to power homes, buildings, factories, and data centers.
Like hydroelectric dams, turbines do this by first converting kinetic energy into mechanical energy. The wind turns the turbine blades, which spin a rotor that is connected to a generator. Inside the generator are magnets that rotate around coils of copper wire, creating a magnetic field that pushes and pulls the electrons within the copper. Voilà — and with gratitude to Michael Faraday — now you have an electrical current that can be distributed to the grid.
Turbines typically require an average wind speed of about 9 miles per hour to generate electricity, which is why they are constructed in deserts, mountain passes, on top of hills, or in shallow coastal waters offshore, where there is less in the way to obstruct the flow of wind. Higher elevations are also windier, so utility-scale wind turbines are frequently around 330 feet tall (though the largest turbines tower 600 feet or higher).
It depends on the size of the turbine and also the wind speed. The average capacity of a new land-based wind turbine in the U.S. was 3.4 megawatts in 2023 — but that’s the “nameplate capacity,” or what the turbine would generate if it ran at optimal capacity around the clock.
U.S. Department of Energy
In the U.S., the average capacity factor (i.e. the actual energy output) for a turbine is more like 42%, or close to two-fifths of its theoretical maximum output. The general rule of thumb is that one commercial turbine in the U.S. can power nearly 1,000 homes per month. In 2023, the latest year of data available, land-based and offshore wind turbines in the U.S. generated 425,235 gigawatt-hours of electricity, or enough to power 39 million American homes per year.
A common criticism of wind power is that it “stops working” if the wind isn’t blowing. While it’s true that wind is an intermittent resource, grid operators are used to coping with this. A renewables-heavy grid should combine different energy sources and utilize offline backup generators to prevent service interruptions during doldrums. Battery storage can also help handle fluctuations in demand and increase reliability.
At the same time, wind power is indeed dependent on, well, the wind. In 2023, for example, U.S. wind power generation dropped below 2022 levels due to lower-than-average wind speeds in parts of the Midwest. When you see a turbine that isn’t spinning, though, it isn’t necessarily because there isn’t enough wind. Turbines also have a “cut out” point at which they stop turning if it gets too windy, which protects the structural integrity of the blades and prevents Twisters-like mishaps, as well as keeps the rotor from over-spinning, which could strain or break the turbine’s internal rotating components used to generate electricity.
Though Americans have used wind power in various forms since the late 1800s, the oil crisis of the 1970s brought new interest, development, and investment in wind energy. “The American industry really got going after the suggestion from the Finns, the Swedes, the Danes,” who’d already been making advances in the technology, albeit on single-turbine scales, Winchester, the author of the forthcoming history of wind power, The Breath of the Gods, told me.
In the early 1970s, the Department of Energy issued a grant to William Heronemus, a professor at the University of Massachusetts, Amherst, to explore the potential of wind energy. Heronemus became “really enthusiastic and built wind generators on the campus,” helping to modernize turbines into the more familiar construction we see widely today, Winchester said.
Some of Heronemus’ former students helped build the world’s first multi-turbine wind farm in New Hampshire in 1981. Though the blades of that farm interfered with nearby television reception — they had to be paused during prime time — the technology “seemed to everyone to make sense,” Winchester said. The Energy Policy Act of 1992, which introduced production tax credits for renewables, spurred further development through the end of the millennium.
Heronemus, a former Naval architect, had dreamed in the 1970s of building a flotilla of floating turbines mounted on “wind ships” that were powered by converting seawater into hydrogen fuel. Early experiments in offshore wind by the Energy Research and Development Administration, the progenitor of the Department of Energy, weren’t promising due to the technological limitations of the era — even commercial onshore wind was still in its infancy, and Heronemus’ plans looked like science-fiction.
In 1991, though, the Danes — ever the leaders in wind energy — successfully constructed the Vindeby Offshore Wind Farm, complete with 11 turbines and a total installed capacity of 5 megawatts. The Blyth offshore wind farm in northern Wales soon followed, with the United States finally constructing its first grid-connected offshore wind turbines off of Maine in 2013. The Block Island wind farm, with a capacity of 30 megawatts, is frequently cited as the first true offshore wind farm in the U.S., and began operating off the coast of Rhode Island in 2016.
Though offshore wind taps into higher and more consistent wind speeds off the ocean — and, as a result, is generally considered more efficient than onshore wind — building turbines at sea comes with its own set of challenges. Due to increased installation costs and the greater wear-and-tear of enduring saltwater and storms at sea, offshore wind is generally calculated to be about twice as expensive as onshore wind. “It’s unclear if offshore wind will ever be as cheap as onshore — even the most optimistic projections documented by the National Renewable Energy Laboratory have offshore wind more expensive than the current price of onshore in 2035,” according to Brian Potter in his newsletter, Construction Physics, though he notes that “past projections have underestimated the future cost reductions of wind turbines.”
Scott Eisen/Getty Images
In the decade from 2014 to 2023, total wind capacity in the U.S. doubled. Onshore and offshore wind power is now responsible for over 10% of utility-scale electricity generation in the U.S., and has been the highest-producing renewable energy source in the nation since 2019. (Hydropower, the next highest-producing renewable energy source, is responsible for about 5.7% of the energy mix, by comparison.) In six states — Iowa, Kansas, Oklahoma, New Mexico, South Dakota, and North Dakota — onshore wind makes up more than a third of the current electricity mix, Climate Central reports.
Offshore wind has been slower to grow in the U.S. Even during the Biden administration, when the government targeted developing 30 gigawatts of offshore wind capacity by 2030, the industry faced financing challenges, transmission and integration obstacles, and limits in access to a skilled workforce, per a 2024 paper in Energy Research & Social Science. That same year, the Department of Energy reported that the nation had a total of 80,523 megawatts for offshore wind in operation and in the pipeline, which, under ideal conditions, could power 26 million homes. Many of those offshore projects and plans now face an uncertain future under the Trump administration.
Though we’re far removed from the 1880s, when suspicious Scots dismissed wind energy pioneer James Blyth’s home turbine as “the devil’s work,” there are still plenty of persistent concerns about the safety of wind power to people and animals.
Some worry about onshore wind turbines’ effects on people, including the perceived dangers of electromagnetic fields, shadow flicker from the turning blades, and sleep disturbance or stress. Per a 2014 systematic review of 60 peer-reviewed studies on wind turbines and human health by the National Institutes of Health, while there was “evidence to suggest that wind turbines can be a source of annoyance to some people, there was no evidence demonstrating a direct causal link between living in proximity to wind turbines and more serious physiological health effects.” The topic has since been extensively studied, with no reputable research concluding that turbines have poor health impacts on those who live near them.
Last year, the blade of a turbine at Vineyard Wind 1 broke and fell into the water, causing the temporary closure of beaches in Nantucket to protect people from the fiberglass debris. While no one was ultimately injured, GE Vernova, which owns Vineyard Wind, agreed earlier this year to settle with the town for $10.5 million to compensate for the tourism and business losses that resulted from the failure. Thankfully, as my colleague Jael Holzman has written, “major errors like blade failures are incredibly rare.”
There are also concerns about the dangers of wind turbines to some wildlife. Turbines do kill birds, including endangered golden eagles, which has led to opposition from environmental and local activist groups. But context is also important: The U.S. Fish & Wildlife Service has found that wind farms “represent just 0.03% of all human-related bird deaths in the U.S.” (Illegal shootings, for example, are the greatest cause of golden eagle deaths.) The continued use of fossil fuels and the ecological impacts of climate change also pose a far graver threat to birds than wind farms do. Still, there is room for discussion and improvement: The California Department of Fish and Wildlife issued a call earlier this year for proposals to help protect golden eagles from turbine collisions in its major wind resource areas.
Perhaps the strongest objection to offshore wind has come from concern for whales. Though there has been an ongoing “unusual mortality event” for whales off the East Coast dating back to 2016 — about the same time the burgeoning offshore wind industry took off in the United States — the two have been falsely correlated (especially by groups with ties to the fossil fuel industry). A recent government impact report ordered by Republicans even found that “NOAA Fisheries does not anticipate any death or serious injury to whales from offshore wind-related actions and has not recorded marine mammal deaths from offshore wind activities.” Still, that hasn’t stopped Republican leaders — including the president — from claiming offshore wind is making whales “a little batty.”
Polling by Heatmap has found that potential harm to wildlife is a top concern of both Democrats and Republicans when it comes to the deployment of renewable energy. Although there has been “no evidence to date that the offshore wind build-out off the Atlantic coast has harmed a single whale … studies have shown that activities related to offshore wind could harm a whale, which appears to be enough to override the benefits for some people,” my colleague Jael has explained. A number of environmental groups are attempting to prevent offshore and land-based wind development on conservationist grounds, to varying degrees of success. Despite these reservations, though, our polling has found that Americans on the coast largely support offshore wind development.
Aesthetic concerns are another reason wind faces opposition. The proposed Lava Ridge wind farm in Idaho, which was Heatmap’s most imperiled renewable energy project last year, faced intense opposition, ostensibly due to the visibility of the turbines from the Minidoka National Historic Site, the site of a Japanese internment camp. Coastal homeowners have raised the same complaint about offshore wind that would be visible from the beach, like the Skipjack offshore wind project, which would be situated off the coast of Maryland.
Not good. As one of President Trump’s first acts in office, he issued an executive order that the government “shall not issue new or renewed approvals, rights of way, permits, leases, or loans for onshore or offshore wind projects” until the completion of a “comprehensive assessment” of the industry’s impacts on the economy and the environment. Eight months later, federal agencies were still not processing applications for onshore wind projects.
Offshore wind is in even more trouble because such projects are sited entirely in federal waters. As of late July, the Bureau of Ocean Energy Management had rescinded all designated wind energy areas — a decision that applies to some 3.5 million acres of federal waters, including the Central Atlantic, California, and Oregon. The Department of the Interior has also made moves to end what it calls the “special treatment for unreliable energy sources, such as wind,” including by “evaluating whether to stop onshore wind development on some federal lands and halting future offshore wind lease sales.” The Interior Department will also look into how “constructing and operating wind turbines might affect migratory bird populations.”
The One Big Beautiful Bill Act, meanwhile, put strict restrictions on tax credits available to wind developers. Per Cleanview, the bill jeopardizes some 114 gigawatts of wind energy projects, while the Center for American Progress writes that “more than 17,000 jobs are connected to offshore wind power projects that are already canceled, on hold, or at risk from the Trump administration’s attacks on wind power.”
The year 2024 marked a record for new wind power capacity, with 117 gigawatts of wind energy installed globally. China in particular has taken a keen interest in constructing new wind farms, installing 26 gigawatts worth, or about 5,300 turbines, between January and May of last year alone.
Still, there are significant obstacles to the buildout of wind energy even outside of the United States, including competition from solar, which is now the cheapest and most widely deployed renewable energy resource in the world. High initial construction costs, deepened by inflation and supply-chain issues, have also stymied wind development.
There are an estimated 424 terawatts worth of wind energy available on the planet, and current wind turbines tap into just half a percent of that. According to Columbia Business School’s accounting, if maximized, wind has the potential to “abate 10% to 20% of CO2 emissions by 2050, through the clean electrification of power, heat, and road transport.”
Wind is also a heavy player in the Net Zero Emissions by 2050 Scenario, which aims for
7,100 terawatt hours of wind electricity generation worldwide by the end of the decade, per the International Energy Agency. But current annual growth would need to increase annual capacity additions from about 115 gigawatts in 2023 to 340 gigawatts in 2030. “Far greater policy and private-sector efforts are needed to achieve this level of capacity growth,” IEA notes, “with the most important areas for improvement being facilitating permitting for onshore wind and cost reductions for offshore wind.”
Wind turbines continue to become more efficient and more economical. Many of the advances have come in the form of bigger turbines, with the average height of a hub for a land-based turbine increasing 83% since the late 1990s. The world’s most powerful offshore turbine, Vestas’ V236-15.0 megawatt prototype, is, not coincidentally, also the world’s tallest, at 919 feet.
Advanced manufacturing techniques, such as the use of carbon fiber composites in rotor blades and 3D printed materials, could also lead to increases in efficiency. In a 2024 report, NREL anticipated that such innovations could potentially “unlock 80% more economically viable wind energy capacity within the contiguous United States.”
Floating offshore wind farms are another area of active innovation. Unlike the fixed-foundation turbines mainly used offshore today, floating turbines could be installed in deep waters and allow for development on trickier coastlines like off of Oregon and Washington state. Though there are no floating offshore wind farms in the United States yet, there are an estimated 266 gigawatts of floating turbine capacity in the pipeline globally.