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The Oscar-winner and El Capitan free solo-er talks to Heatmap about solar panels, fatherhood, and his new docuseries, Arctic Ascent.

In 2017, rock climber Alex Honnold went on Jimmy Kimmel Live! to promote Free Solo, the then-new documentary about his unassisted climb of Yosemite’s El Capitan. “Is there anything bigger than that?” Kimmel prompted as a closing question.
“I mean, there are technically some bigger walls in the world,” Honnold said. “But they’re in very remote places — like Greenland.”
Five years and an Oscar later, Honnold was scrambling off a boat at the base of Ingmikortilaq, a crumbly sea cliff that towers nearly 1,000 feet higher than El Cap over an iceberg-ridden fjord in eastern Greenland. His intended first ascent was the culmination of a six-week adventure across ice fields and glaciers.
This time, Honnold wasn’t alone. The Greenland expedition included two other legendary climbers, Hazel Findlay and Mikey Schaefer, as well as Aldo Kane, who provided safety and technical support; Adam Kjeldsen, a Greenlandic guide; and perhaps most surprisingly, Heïdi Sevestre, a French glaciologist who helped set up or run 16 different studies to collect data for scientists around the world.
The team’s adventure is captured in Arctic Ascent with Alex Honnold, a three-part docuseries that premieres on Hulu and Disney+ on February 5. Ahead of its release, I spoke separately with Honnold and Sevestre about the expedition, the importance of climate science, and their respective climbs. (While Sevestre, previously a non-climber, didn’t attempt Ingmikortilaq, she did scale a 1,500-foot rock face known as the Pool Wall while drilling rock cores for samples.) Our conversations have been lightly edited and condensed for clarity.
Unlike a lot of other outdoor sports like mountaineering or skiing or even surfing, rock climbing doesn’t seem as obviously imperiled by climate change. How did this become the cause you wanted to devote your time and money to?
Oh, I think climbing is more imperiled by climate change than most other sports. I mean, you’re right that maybe it’s not as impactful as to skiing, but it’s way more impactful than almost every other sport.
You’re still in the mountains. Wildfire smoke every summer — that’s now a thing that just didn’t exist when I was growing up climbing. Even if you’re just rock climbing, you’re always approaching in the mountains. Nowadays, most couloirs [chutes between rocks that might typically fill with snow in the winter] have melted out. Stable snow fields that have existed for generations are now melted out. Piles of teetering rubble are falling down mountainsides, and also a lot of routes are just less safe. The mountainsides themselves are collapsing, like the Aiguille du Midi gondola in Chamonix. Which, actually — one of the things we were installing in Greenland were temperature sensors on one of the cliffs, related to studying how rocks thaw out, what happens when permafrost melts. I would say that climate change is still incredibly relevant for us.
Your way into climate was through your climbing, then?
A big part of my environmental awareness in general is because of the experiences I’ve had outdoors as a climber. But long before [the Greenland expedition], I started a foundation in 2012 where I’ve been supporting community solar projects around the world and caring about the transition to renewables. I’ve cared about climate change forever. I think this was just the first opportunity to do it on mainstream television.
I saw that Arctic Ascent purchased carbon credits to compensate for production emissions. I was hoping you could talk about that decision, and how else you might have minimized your impact on the expedition, since I don’t think people are aware of how energy intensive film and TV productions can be.
In this case, other than the obvious expense of all of our flights getting to Greenland, we had a relatively low carbon footprint because we were camping the whole time. I think you’re right that a lot of television is kind of insane when you have all the RVs and everyone’s in their own thing and there’s hair and makeup and it’s just crazy with, like, a million cameras. In this case, it was basically a bunch of people camping on a glacier for six weeks, so it’s not quite the same as a Hollywood set.
But yeah, I think the idea to purchase offsets was the obvious bare minimum for a project like this. If you’re going to be doing a whole story around sea level rise, you have to do something.
The Honnold Foundation focuses on bringing solar panels to vulnerable communities, but these are fairly small projects compared to the expansive solar farms we might more traditionally think of. Why did you choose to focus your time on something that might seem, at least on paper, to be of a smaller scale than, say, electrifying the grid?
It’s a totally fair question. In 2012, it wasn’t totally clear that the world was transitioning to renewables at all. It seemed like it was inevitable, but you’re never really sure — you know, back then people were into hydrogen and you’re like, “Oh, maybe we’re going to have hydrogen cars, or maybe battery electric really takes off,” blah, blah, blah. Anyway, now it seems totally clear that the world is transitioning to renewables. Within some timeframe, like 20 to 50 years, the world will be 100% renewable.
The thing is, we currently live in a world where something like a billion people don’t have access to power, and transitioning to renewables will still leave us in a world where a billion people don’t have access to power. [Editor’s note: The number of people living without electricity today is actually closer to 760 million.] As the system changes, there are so many people who are left behind. What the Honnold Foundation tries to do is find that sweet spot in helping with the transition, helping the people who are being left behind.
Part of that is just by necessity — I’m a professional rock climber, I’m not a tech billionaire. So the small-scale grants just make more sense to some extent, but they also have the biggest impact on human lives because when you do these small-scale projects, you can fundamentally change the way people live. That’s a huge impact.
I live in Las Vegas, and you see huge solar farms around the desert. It’s great; the grid is going 100% renewable. I’m into that. But realistically, the only difference it makes in most people’s lives is maybe a small change in their utility rate. Really, the people that benefit are the utility shareholders — it’s some Warren Buffett-owned utility in my case, NV Energy. That really isn’t that inspiring. This is my long rant to say that the Honnold Foundation is trying to help the humans who need it the most.
Did you get a chance to use solar panels on the Greenland expedition?
On this trip, no, because they were running a generator for production and it was charging, like, 50 batteries.
It’s funny because we did an expedition in Antarctica where we made a little climbing film as well. And on that trip, they planned to take a generator and then somebody just forgot the fuel. So we got there and we were like, “Oh, no,” and we wound up doing the whole trip off solar and it totally worked.
This was your first expedition since becoming a father. You’ve worked on the climate cause for a long time now, but I’m curious if your perspective has changed at all since your daughter June joined your family — and I know you have another daughter on the way!
Yeah, soon! No, I don’t think my perspective has changed too much. I’ve always cared about these kinds of issues. The bigger change is in the way that I spend my time. Having a family forces me to be a little bit tighter about the choices that I’m making, what expeditions I choose to go on. That makes a trip like this even more worthwhile, where you get to do great climbing and there’s a real purpose behind it, and you get to share important knowledge about things that matter.
Can you tell me a little more about the decision to bring Heïdi on board? I heard her version of the story earlier this week but I’m curious about how you found her and roped her in.
Isn’t she so amazing?
She was delightful!
That’s the thing with Heïdi. Because when you spend time with her, she just makes you care about about ice. And I don’t even like ice. It’s not my thing; I like rocks. But she made me much more knowledgeable and much more caring about that type of world.
Do you consider yourself an optimist when it comes to climate change?
I think so, which is weird because I’m optimistic despite all the data to the contrary. I understand the predictions, but there’s so much to gain. So far it’s been 20 years that I’ve been reading environmental nonfiction and we haven’t really chosen to make anything of this opportunity, but we still have this incredible opportunity to build a better world to live in, a cleaner world. We can still choose that at any point. And I just keep thinking that at some point, we’re going to choose it. You can’t keep ignoring the obvious thing forever.
How did you get involved in the Arctic Ascent expedition?
This was an absolute dream come true for me — I felt extremely lucky to get a call from the team. It is extremely challenging to go to that one remote location, one of the least studied places on Earth. But Alex, as you know, is a firm believer in the scientific work. The planets really aligned. It took about a year prior to the expedition to design the work we could do with boots on the ground.
I wanted to know what it was like to put together scientific objectives for an expedition like this. It’s a little bit unconventional because there’s a film crew and there was climbing involved.
I think it was extremely brave and extremely daring of the entire team to have the willingness to invite the scientists on board. Because not only did we have the best climbers in the world climbing in a very challenging and hostile environment, we’re also filming a series of documentaries and we have to do some of the very best possible science. So it’s not that easy! But what we did is, we took it step by step. We contacted all the universities and labs and institutions interested in data from this part of the world — and also interested in training me on how to collect this data. Because I really felt — it’s what I was thinking the whole time — I really felt like I was an astronaut on the ISS. I was the only one, and I had to do the best possible work.
We ended up with 16 different protocols to do on this expedition, so it was really major. And, you know, we worked with NASA, we worked with research institutes in Denmark, the University of Buffalo, and the University of Kansas, for example. So it was challenging but a dream come true to be trusted by the scientists.
Your first big polar expedition was actually to Greenland, back in 2011. Had you been back to the island between that research trip and this one?
I had spent a tiny bit of time — not so far in the field as East Greenland, but around the coastlines. But what I was doing there was mostly science communication with people who wanted to learn about the impacts of climate change on the Greenland ice sheets. So I hadn’t been on a big research expedition to Greenland since 2011. And the changes were absolutely massive.
That was going to be my question!
The Arctic is one of the fastest-warming places on Earth. Everything that’s taking place in Greenland is impacting the rest of the world, so I felt that we had a duty and a mission — on top of climbing these incredible monoliths, we actually had to bring something back to society.
In the series, you talk about how remote and understudied East Greenland is by climate scientists. But during the expedition, you were being assisted by support helicopters and by boats. So why aren’t expeditions like this one happening all the time? Is it an issue of funding or a lack of scientific interest in this particular region?
It’s crazy to think of how little data we have from the ground [in East Greenland]. We have satellites — we have as many satellites as we want. But it is very tricky to get there. What you have to understand about this place is that for 10 months of the year, there is sea ice blocking access to this field. Ten months of the year! So the rest of the year — yes, we can access by plane, we can access by boat, but it’s very expensive.
What was great about this project is that we had in mind, “How can we lower our carbon footprint?” This is why, for example, we worked with fishermen who had boats from a nearby village at the entrance of the field. It was very important for us to use local means of transportation. Of course, we had to use helicopters every now and then, because there was no other way. But it’s remote, it’s expensive, and on top of everything, it is extremely hostile.
Oh my gosh, the bashing you get when you go there! This is something that we really wanted to show in the series — how powerful nature can be. And climate change is accelerating and making these changes even more violent. So I think it’s important to show that when nature starts to be a bit destabilized, it can get very angry.
There was a paper in Nature that came out earlier this month that said nearly every glacier in Greenland has thinned or retreated over the past few decades. In the series, there’s a bit of good news, which is that the Daugaard-Jensen Glacier is a little bit more stable than you were anticipating. Do you have any insight into why that might be?
What’s so great is, it keeps part of the mystery! I like that we still don’t totally understand what’s taking place.
The scientists we’ve been working with have told us — this is a bit technical — but it has to do with the shape of the bedrock. It seems that the glacier is resting on a little ridge that might be holding everything together. This might be the reason why the glacier is still stable; also, this part of Greenland still receives a lot of snow.
But we’ve seen some cracks in this perfect picture. You know, the NASA float [that we launched on the expedition] has told us that the temperature of the water in the fjords is increasing. So it’s not all perfect. The environment around it is definitely changing, but it seems that it has some advantages.
Were there any findings from the expedition that you are particularly excited about?
All of them! But science takes a very long time, so at the moment, we’re still waiting on a lot of the results from these different protocols. But what I want to share is something that is very simple: Greenland holds a lot of ice, and if we lose the ice, it means 6 to 7 meters of sea-level rise. As you saw in the paper that was published by Nature, at the moment, Greenland is losing 30 million tons of ice per hour. What is crucial to understand is that every action we conduct back home to reduce our carbon footprints and to preserve our climate helps Greenland and helps our collective future. All this data will help us to prepare for the things to come.
Last question: Have you taken up rock climbing?
I’ll be honest: no. I think I’m a bit traumatized in a good way. I think I needed a minute to recover. But I really want to start climbing again — now, with the launch of this series, I know that it’ll be my mission for this year. Otherwise, I think Alex and Hazel will never forgive me.
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Where is the smoke worst, where will it go next, and what causes that color?
Before wildfire smoke turns the skies to a jaundiced yellow-gray, it might look almost pretty. Midday light grows diffuse, taking on a crepuscular golden hue. Shadows soften and stretch long. The sunsets are particularly incredible: radiant, neon red.
But as with oleander and poison dart frogs, beautiful things are often the most dangerous. The same wildfire particulates that scatter the light will, once dense enough, turn the air around you orange, then black. They will get into your lungs — slipping past your nose hairs and mucus, the body’s defenses that stop larger particulates — and provoke your immune system into an attack. The tiny air sacs at the ends of the bronchioles in your lungs, where the gas exchange of “breathing” actually happens, will become inflamed. You will become short of breath. You will cough. The smallest smoke particulates may even enter your bloodstream.
And if you are like 24,000 other Americans every year, this will kill you.
Though wildfire smoke exposure might seem to be more of a nuisance to a healthy person than anything else, experts agree it should be taken seriously. “In my profession, wildland firefighting, you make a decision that you run into that,” Nicholai Allen, a firefighter and founder of Safe Soss, a home-hardening product line, told me. “But for my family and my children, I don’t want them breathing in the smoke that’s traveling that far. We have air purifiers, and we’re taking similar precautions.”
On Wednesday, more than 100 million people in the Midwest and Northeast face unhealthy smoke conditions from fires burning up to 2,000 miles away. Here’s what you need to know.
The smoke is largely coming from 150 or so lightning-ignited fires in Ontario and northeastern Minnesota. Triple-digit temperatures, dry conditions, and high winds have fanned a “wall of fire” across the region, as the firefighting newsletter The Hotshot Wakeup put it, even as Canada is, on the whole, tracking behind its five-year average for area burned so far. Most of the fires sending smoke to the U.S. this week are still out of control and spreading rapidly.

A high-pressure area over the central U.S. and a low-pressure area over Eastern Canada are acting as a funnel, pulling bad air east across the Great Lakes region and into the populous Acela Corridor. Conditions are worst closest to the fires: Around 8 a.m. on Wednesday morning, Duluth, Minnesota had a “hazardous” air quality rating of 785 out of 800. By the afternoon, Toronto had the worst air quality of any major city in the world, and drivers in northern Michigan have been advised to slow down and turn on their low-beam headlights because visibility has been so reduced by the smoke. The eastern-moving plume has also blanketed large portions of Upstate New York.
Degraded air quality reached the Boston and New York City areas on Tuesday night and is expected to linger through Thursday. The smoke reaches as far north as Maine, having dimmed the morning light in New Hampshire, and could spread as far south as Washington, D.C. over the next 24 hours.
Though the smoke is staying largely to the north over the middle part of the country, forecasts show it could dip into downtown Chicago on Thursday as well.
Wednesday and early Thursday will be the worst days for the eastern U.S., per the current outlook. A cold front should help push the worst of the smoke out of the region as we head into the weekend.
So far it appears that much of the smoke has remained high enough in the atmosphere that while you’ll be able to see and likely smell it, it might not cause extreme air quality problems on the ground. As of Wednesday afternoon, New York City was recording some of the worst air on the East Coast, with an air quality index of around 160 — bad enough to trigger an “unhealthy” alert for the general public and to rank fifth-worst among major cities worldwide. The rest of the region still mostly showed orange readings designed to alert sensitive groups such as older adults, people with respiratory conditions, and pregnant women, or more moderate yellow ratings.
Conditions could still change, though. Heat, pressure, and winds can drive smoke down to ground level, where it becomes a threat to public health. In fact, the Fox Forecast Center’s models indicate that particulate matter concentrations around the Great Lakes and Northeast could be on par with the 2023 East Coast smoke event, during which New York had the world’s worst air quality, although The New York Times reports that “even the most severe forecasts” this week should not approach that level.
The best thing to do is to continue monitoring your local air quality. If you want help navigating what those readings mean, my colleague Emily Pontecorvo has written a great explainer.
For many on the East Coast, the orange skies are a flashback to the 2023 smoke event. While eerie and apocalyptic, the smoke also gives us an excuse to talk about Mie theory.
Air molecules are much smaller than the wavelength of light. When white light from the sun enters the atmosphere, nitrogen and oxygen scatter the short, higher-frequency blue light in multiple directions. This is known as Rayleigh scattering, and is also the answer to, “Why is the sky blue?” Under normal conditions, wherever you look in the sky, blue light is headed toward your eye.
Smoke particles, while small enough to enter our lungs when inhaled, are larger than air molecules — about the same size as light wavelengths. Because these particles are larger, they also scatter light more democratically, including the lower-frequency, longer reds and oranges. This is called Mie scattering. When sunlight passes through smoke, the reds, oranges, yellows, and blues are all mixed together as they reach our eyes, appearing as a hazy gray or white.
You might expect thicker smoke to result in a darker gray, then. But smoke also contains organic compounds from burned plants called brown carbon, plus soot, both of which absorb visible light. Brown carbon, in particular, prefers light at the shorter end of the spectrum, absorbing about three-quarters of the total light at blue wavelengths in smoke plumes, compared to about half at red wavelengths. That means that when the smoke thickens, the blue light doesn’t reach our eyes nearly as well, and the sky takes on an orange appearance.
One of the dangers of the current smoke event is that it coincides with high temperatures across the Central U.S. and New England. Both conditions together — high heat and smoke — can lead to some confusion over how to respond.
The best strategy is to keep your windows closed. But while it might feel safe side, wildfire smoke can still degrade indoor air quality. “If you have a fresh air intake on your air conditioning system, I would shut that off so that you’re recirculating just your purified air inside your house,” Allen, the firefighter, told me.
You can also install activated carbon exterior filters on attic and crawl space vents and run a purifier with a HEPA filter. (If you bought an air purifier during the last smoke event, consider this your reminder to replace your filter.) “Then I would avoid going outside or exercising outside if there’s smoke in the air,” Allen added. “When the particles are arriving to you from a great distance from the wildfire, they are the smaller particles that can get in your lungs. So not to create undue fear, but there’s definitely stuff in that air that you don’t want to breathe.”
Deciding what counts as a heat death is more difficult than it sounds.
Just last month, a heat wave killed an estimated 2,700 people in France. Think about that for a second: 2,700 people. That’s equivalent to the mortality of two Hurricane Katrinas or 10 Hurricane Sandys. In France, where there were roughly 970 murders in 2024, the heat wave killed more people in two weeks than almost three years’ worth of homicides.
But unlike floods, hurricanes, tornadoes, or murders, heat doesn’t leave behind much of a crime scene. Although heat kills people in obvious, direct ways like heat stroke, it also puts enormous strain on our hearts and kidneys as our bodies work to keep our internal temperature at 98.6 degrees Fahrenheit. Heart attacks spike during heat waves because vasodilation diverts blood to the skin’s surface to cool it down, in the process lowering blood pressure and forcing the heart to work harder and faster to circulate oxygen. Deaths from renal diseases also jump during periods of high temperatures due to severe dehydration and restricted blood flow to the kidneys.
“Let’s say you have two people with underlying heart disease; somebody has a heart attack versus somebody has a heart attack because it’s too hot,” Kristie Ebi, an epidemiologist at the University of Washington and an expert on heat-related mortality, explained to me. “Will the second one be recorded as a heat death or will it just be recorded as a heart attack? Frankly, when both go into the emergency department, the number one goal is to save a life — it’s not necessarily to record whether it was because of temperature.”
But if physicians don’t code the second heart attack as a heat death— a procedure designed for insurance and billing rather than getting to the root of underlying environmental conditions — then the headline number of heat wave-related deaths will almost certainly be an undercount. In Washington during the 2021 heat dome, for example, the state health department initially reported that 129 people died from the temperatures. But later analyses compared the overall number of people who died that week in the state to the average number of people who died during the same week from 2013-2019 and concluded that there were 485 “additional” deaths compared to what would have been expected during normal early summer conditions.
Those 485 deaths are called “excess deaths,” and the number offers a broader picture of who actually dies from a heat wave. The tally captures not only those heart attacks that are coded by physicians and medical examiners as caused by the heat, but also the ones the state may have overlooked or discounted. Air pollution deaths, homicides, drownings, and accidents, for example — all of which also spike in relation to heat waves — show up. As one epidemiologist explained it to the Seattle-area NPR affiliate KUOW, a boating death might count as an excess heat death, too, because while “not directly attributable to heat in the sense of heat stroke … it arguably is attributable to heat in the sense that had it not been hot, they would not have gone out.”
Excess death analyses are also methodical in what they don’t count. “After a heat wave, there’s a deficit in the number of deaths, which means that the heat wave brought forward deaths that would have occurred anyway,” Ebi told me. The analyses also take those into account to model only the “true” excess events. This, at least, is relatively simple in scope: The advantage of heat waves for mortality accounting is that they don’t have the long tails associated with hurricanes and other weather-related tragedies. “Deaths occur over a few days of a heat wave, and then it’s over,” Ebi added.
But the calculation, while relatively straightforward, has its critics, too. “The limitation of that approach is that it doesn’t actually quantitatively attribute that excess mortality to the heat,” Christopher Callahan, a climate scientist and assistant professor at Indiana University Bloomington, told me. Take the boating accident example: Maybe if it’d been a regular summer day, the enthusiast still would have taken his pontoon out and had all those beers. Maybe during the heat wave it was also smoky, and that caused some of the excess deaths. There’s also the possibility that the baseline number of deaths already includes some baked-in heat-related deaths, obscuring the cumulative total.
A third approach, favored by academics — and recently employed by Callahan to estimate the 2,700 heat-related deaths in France last month — involves using long-term data on both temperatures and mortality for a given location and then fitting a statistical model that relates the two. This method has the advantage of generating a U-shaped relationship that shows how mortality rates change once temperatures exceed a certain threshold (or drop below it, in the case of cold-weather-related deaths, hence the “U”). Like an excess death analysis, this method “has the benefit of, again, not having to rely on individual diagnoses,” Callahan said. “It has the drawback that there is no one right statistical model. Different people have different philosophies about how to fit those models.”
The other drawback is that creating such a model and subjecting it to the rigor of peer review is time-consuming — by the time you’re able to publish a death toll, the news cycle has probably moved on. Callahan got lucky: He had already created such a model for France to study the 2003 heat wave, which killed an estimated 15,000 in the country in a couple of weeks. The model relies on a historical understanding of the relationship between temperature and mortality in France — “not a crazy assumption, but an assumption,” he admitted to me — and he published the findings in Carbon Brief earlier this month. (Callahan also estimated that 20,000 people died continent-wide in Europe during the June 2026 heat wave — a number that circulated widely, but that he told me he’s now working to revise downward.)
Notably, the number Callahan arrived at for France does not represent “real” people or “real” deaths, at least as linked to death certificates. There are no biographical or even demographic numbers attached to it. (That said, you can create models of the same U-shaped relationship for anything: temperature and age, income, race.) More mind-bending, though, is that because of this, Callahan’s model can also be used to predict. Had there been a way to know the exact temperatures before the European heat wave, he could have told you how many people would likely die before they actually did.
In the case of France, the simple excess death count put the toll at 2,025, though officials say they expect the number to rise. While Callahan’s number and the official tally from France differ by what seemed to me to be a lot — 675 deaths — Callahan told me he’s actually encouraged by how close his model came to the government’s empirical count, given that the two use completely different methodologies.
After all, heat death counts can vary by orders of magnitude, including within a single government. Before 2020, the Centers for Disease Control and Prevention reported that only about 700 Americans died each year from heat, relying primarily on physician diagnostic codes. After moving in recent years to better incorporate underlying and contributing causes of death, the CDC adjusted its estimate upward to about 2,000 heat-related deaths per year in the United States. Still, the government’s numbers remain extremely conservative; independent researchers studying heat mortality say the figure is likely closer to 12,000.
But even more holistic heat-related mortality numbers have their critics. For example, models don’t work as well for many lower-income countries, where mortality may be reported monthly, thereby making day- or week-level heat attribution impossible.
Granularity presents its own set of problems. Excess deaths and modeling analyses both have to define the first “heat day” of an event. You can do that by setting a fixed threshold — say, anything above 90 degrees Fahrenheit counts as “high heat” — but Ebi told me there is little value in analyses or policies that take that approach. That’s because heat is contextual: “My standard joke is, if we had the temperatures here in Seattle that they have in Phoenix, we basically all die, because we don’t have the infrastructure and we’re not acclimatized,” she said.
A slightly better metric might be a relative threshold — say, temperatures above the 95th percentile of historical temperatures for a specific location count as “extreme heat.” The problem there, though, is that it may need to be stratified further by vulnerable populations that feel the effects much sooner, like adults over the age of 65, pregnant women, outdoor workers, or people with certain medical conditions. While that approach might seem overly complicated, parts of Asia already use nuanced thresholds to warn older adults to take precautions. “It’s going to be more challenging to communicate, I grant you that,” Ebi told me of such an approach — much less to try to model. “But it’s also going to be more useful.”
Even so, a larger problem remains: The multiple systems for calculating heat deaths are honed to address different questions, which makes them impossible to compare. The Federation of American Scientists has pushed for the CDC to upgrade and standardize its heat-mortality tracking. “We’ve thought about if it’s possible to ever set a goal of bringing heat-related deaths down by 50%, or something like that,” Grace Wickerson, the senior manager of climate and health at FAS, told me. “But we don’t even have a baseline number or a way to say, ‘This is the starting point for this goal or strategy.’”
Wickerson also suggested, though, that there might be things we lose in trying to nail down the most correct heat-related mortality number. “I’m almost a bit weary of the pursuit of large numbers,” she said. “At least to me, what feels more important is why people are suffering and dying, what types of people they are, and what stories, messages, and stakeholders we need to engage and target to actually build meaningful policy strategies.”
Despite being deeply engrossed in the calculations, Callahan stressed that he wants readers to have a similar takeaway from his own research. Improved “healthcare access and access to cooling, shade, and shelter” — or in the case of heat-related mortality from climate change, “reducing greenhouse gas emissions” — lead to fewer heat deaths, meaning the vast majority are preventable.
“The relationship between environmental conditions and a person’s mortality is not fixed or necessary,” he told me. “It can be stopped.”
Current conditions: Canadian wildfires smoke has returned to the Northeast United States, worsening air quality across the region • Catastrophic 1-in-1,000-year floods devastated Missouri’s Black River region, right as intense rainfall is headed for Texas • Temperatures in Beijing are set to drop by nearly 10 degrees Fahrenheit after roasting at nearly 100 degrees yesterday.
PJM Interconnection just released the results of its latest capacity auction for 2028 to 2029, and the nation’s largest grid system maxed out its prices yet again. The clearing price hit its cap of $325 per megawatt-day, all while PJM failed to line up enough supply to meet its incoming demand with a sufficient margin of safety. “These auction results show that demand for electricity continues to grow faster than electricity supply,” PJM CEO David Mills said in a statement. “At the same time, PJM recognizes how this supply-and-demand imbalance impacts the reliability of the system and costs for consumers. We are working with government and industry leaders on multiple fronts to restore that balance by bringing on new generation as fast as possible and managing the growth of new load on the grid.” But Julia Kortrey, the director of strategic initiatives for state-level programs at the climate advocacy group Evergreen, said PJM had just “delivered more bad news for people already struggling with higher energy bills,” and accused the grid operator of slow-walking “cheap, clean energy that could lower bills.”

Back in April, I told you about Clean Core Thorium Energy. The Chicago-based startup is dusting off a decades-old dream of harnessing abundant thorium as a fuel for nuclear reactors to replace uranium, which is rarer and produces more long-lived radioactive waste. In the spring, the firm inked a handful of deals to begin manufacturing its first fuel assemblies using thorium. Now, I can report exclusively, Clean Core has surpassed a technical milestone for its fuel with the publication of a comprehensive peer-reviewed engineering assessment in the journal Nuclear Engineering and Design. The paper comes after the company completed a multi-year campaign of irradiating the fuel at the Idaho National Laboratory’s Advanced Test Reactor. The results showed that the fuel can be used in an existing pressurized heavy water reactor, like those that make up the bulk of the Canadian and Indian fleets, and achieve a high “burnup” of the material. “Milestones in this industry are earned in reactors, not in renderings,” Mehul Shah, Clean Core’s chief executive and founder, told me in a statement. “The analyses underpinning the fuel’s design have now withstood the scrutiny of peer review in one of the field's leading journals.”
Google has agreed to buy the entire initial output of a sweeping solar project in Arkansas in a bid to offset its fossil fuel emissions. On Tuesday, the Financial Times reported that the tech giant would purchase the full 1.6 gigawatts of solar power and 2 gigawatt-hours of battery storage from the first phase of construction on the Steel River Energy Center, set to be complete in 2029. The second phase will up the output to 2.5 gigawatts of solar and 2.9 gigawatt-hours of storage. The panels will all come from First Solar, the U.S. manufacturer that boasts a 100% domestic supply chain. None of Google’s data centers will use the electricity, but the power will serve as an offset to gas-fueled operations elsewhere.
It’s hardly the only bullish sign for solar. In June, Europe generated a quarter of its power from photovoltaics for the first time, according to an analysis by the renewables-focused think tank Ember. “Solar’s rise has been truly stratospheric, beating prediction after prediction,” Chris Rosslowe, a senior energy analyst at Ember, said in a statement. “In just a few years solar has gone from a small player to an essential part of Europe’s power system, as governments and citizens look for low-cost, quick-to-install domestic power sources.”
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You can’t make it here, but you can — at least, for now — make it anywhere else. New York Governor Kathy Hochul signed an executive order Tuesday enacting the nation’s first state-level moratorium on building large-scale data centers. The one-year pause “will ensure New Yorkers are not paying for transmission and infrastructure build outs” and will give Albany time to create a statewide investment framework to direct more benefits from projects to local communities, the governor’s office said in a press release. “New York will lead the way in creating the strongest standards in the nation for data center development, ensuring that when companies succeed because of New York, New Yorkers succeed too,” Hochul said in a statement. She also vowed to press the legislature to pass a bill to repeal sales tax exemptions from large data center projects.
It’s no surprise. At least seven in 10 Americans oppose data centers built near their homes, Heatmap Pro polling showed last month. That’s at least partly driven by the perception that data centers are driving up electricity costs. Utilities requested $18.6 billion in electric and gas increases in the first six months of this year, according to a new report from the grid-focused nonprofit PowerLines. More than $9 billion of those requests were filed in the second quarter of this year alone, surpassing the total for the same period in 2025 — which was itself a record — by 26%. “Summer is when Americans pay attention to what electricity costs because their utility bills are often higher,” Charles Hua, PowerLines’ founder and executive director, said in a statement. “The amount of utility rate increase requests in these filings shows the pressure on household energy bills isn’t easing.”
Realta Fusion, a magnetic mirror fusion startup, announced plans Wednesday to convert an iconic former Oscar Mayer plant in Wisconsin into its corporate headquarters and research hub. As part of the deal, the state and its capital city of Madison will contribute $55 million to support the conversion. The facility will employ more than 600 people in technical and non-technical roles. “We spent the better part of the past two years searching across the country to find the most favorable business environment and the most attractive site to build our R&D facility, and we found it in our own backyard,” Realta CEO Kieran Furlong said in a statement. “The state of Wisconsin and the city of Madison have made it clear they understand the promise of fusion energy and share our vision for the future, and now they’ve thrown their lot in together to make that vision a reality.” It’s yet another sign, as my colleague Katie Brigham put it in 2024, that fusion is “finally, possibly, almost” here.
Meanwhile, some fission news: Remember when I told you last month about why I try to cover all the major milestones in China’s nuclear construction projects? Well, I have another update: China General Nuclear, one of the country’s two main state-owned nuclear companies, just installed the reactor pressure vessel for unit 1 of the Lufeng nuclear plant in Guangdong province. In a statement to World Nuclear News, CGN, as the company is known, said the latest item off the construction checklist marks “the beginning of the peak period for the installation of main system equipment in the nuclear island of unit 1 and lays a solid foundation for the orderly progress of subsequent key processes such as the installation of main pipelines.”
There are thousands of ways to pull a climate or energy angle out of Russia’s ongoing war in Ukraine. Here’s one: Tajikistan isn’t receiving as much Russian oil and gas as before, given Ukraine’s campaign of drone attacks on key pipeline and refinery infrastructure, so it’s looking to ramp up its own drilling operations again. On Monday, the Times of Central Asia reported that Tajik Energy Minister Daler Juma said the country had only enough fuel to last about two months.