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We know dangerously little about how hot it’s getting inside.
If the last few weeks are any indication, this summer is going to be a scorcher.
In Spain and Portugal, April temperatures reached record highs. A heat wave swept through Asia, killing dozens on the Indian subcontinent; temperatures in the region hovered around 110 degrees Fahrenheit for days. The United States saw records break throughout the Northeast and Midwest, with temperatures into the 90s.
And that’s just how hot it was outside. Inside is a completely different story — one we know far less about.
Heat is the deadliest extreme weather phenomenon in the United States, and when the outside world is boiling, the advice is often pretty simple: get inside. But the majority of heat-related deaths happen indoors, and, unlike the satellites and weather stations that can measure outdoor temperature, we have very little data on just how hot our homes are getting.
That’s a major blindspot. Without knowing exactly how hot buildings are getting, lawmakers have little, if any, data to rely on when it comes to crafting policies around indoor heat. A WHO report from 2018, which lays out a strong recommendation for a minimum heat threshold of 18 degrees Celsius (about 64 degrees Fahrenheit), simply suggests that, when it comes to heat, “strategies to protect populations from excess indoor heat should be developed and implemented.”
“Humans spend the majority of their time indoors, and we have entire building stocks across our cities where we haven’t taken into account what the weather systems around those buildings are going to look like,” said Vivek Shandas, a professor at Portland State University who studies heat in urban environments and advisor to CAPA Strategies, a climate data consultancy. Regional architecture gave way to cheap steel and concrete around the country, and the result has been residents being put at risk by the very nature of their homes.
A new study from the city of Portland, Oregon, one of the first of its kind, goes a little way towards closing the indoor temperature data gap. In the wake of an intense, deadly heat wave that killed 123 Oregonians in June 2021 — locals called it a heat dome, for the hot air mass that parked itself over the region for days — the Portland Bureau of Emergency Management (PBEM) commissioned CAPA Strategies to find out just how hot the homes of the city’s residents were getting. In particular, they looked at three properties managed by Home Forward, the city’s housing authority, which had each seen resident deaths from heat-related illnesses.
The setup was simple: Residents volunteered to have temperature sensors placed in their units — usually away from an air conditioner, if they had one. The sensors then monitored indoor temperatures over the summer of 2022, which while not quite as hot as 2021’s heat dome, still brought intense heat to the region. If indoor temperatures got above 80, 85, or 90 degrees Fahrenheit, residents got an alert that would, ideally, nudge them into taking action to protect themselves from heatstroke.
And the apartments did get hot, though not quite as hot as the outside world: Interior temperatures maxed out in the low to mid-90s on 100-degree days, and every apartment in the study tipped over 80 degrees on multiple days. Units in two of the residences, which were built with concrete, stayed hot for longer even as nighttime temperatures fell outside. (Units in the third residence, which was built out of wood, were far better at cooling down.)
That kind of heat is striking: Prolonged exposure to temperatures that high can be dangerously hot, especially for elderly people or anyone with a medical condition that makes them susceptible to heat, though none of the residents who participated in the study suffered any serious medical impacts.
To get an idea of how that indoor heat affected residents in less life-threatening ways, the researchers also periodically sat down with them to conduct surveys and workshops. They found that residents experienced some sort of heat stress — difficulty sleeping, headaches, or even just heightened irritability — throughout the summer, not just during heat waves.
“It was disheartening to see how much heat stress many building residents are putting up with all the time,” said Jonna Papaefthimiou, who was the city’s chief resiliency officer at the time of the study and recently left for the same role at the state level. The residents of the Home Forward buildings dealt with particular obstacles that might not have been present in other houses, like a lack of mesh screens that discouraged residents from opening their windows at night for fear of intruders, whether insect or human. “There were a lot of barriers for people to just do basic things to cool off,” Papaefthimiou told me.
But they also tried to take care of each other, she said. Many of the residents signed up for the study out of a desire to help their neighbors and better understand heat risks in their building, including a person whose apartment had previously been the home of one of the victims of the 2021 heat dome. Mutual aid is a simple, if underappreciated, climate-adaptation practice, and this kind of community involvement can save lives: Over the course of the study, the researchers found that residents were eager to learn how to check in on and help each other during heat waves.
While there’s certainly a lot of work that governments need to do to help their citizens deal with extreme heat, Papaefthimiou thinks this desire to help is an encouraging sign. “Neighbors helping each other does not represent a failure of government to me. It actually means that something's going well in the community as a whole,” she told me.
For the most part, cities across the country have dealt with heat by letting developers and residents throw air conditioning at the problem. It’s an effective, if blunt, tool — the best one we have in a heat wave, really — but it’s by no means perfect. Air conditioners are energy-hungry, which makes them expensive to run, often out of reach for lower-income residents, and vulnerable to black outs when everyone turns them on. They also struggle to cool buildings on particularly hot days. That’s especially true if they’re, say, window AC units in buildings that were never designed with cooling in mind, as is the case with many cities in the northeast.
Most of the buildings in Portland were built for a different climate than the one that exists today and will need to be retrofitted to adapt for a changing climate, Papaefthimiou told me. This is true of cities across the country, and each one will be forced to reckon with an associated host of questions as a result, from what the best approach to retrofitting is (passive cooling might be a better investment than air conditioning in some instances, for example) to whether that process will end up pricing people out of the places they live in now.
The Portland indoor heat report includes a number of recommendations for what the city’s government can do to help its citizens, from the short-term (distributing things like thermal curtains and magnetic window screens) to the medium- and long-term (retrofitting buildings with central AC or providing professional insulation services). But the study is limited — only 53 residential units participated over three months — and researchers at CAPA are hoping to secure funding from Multnomah County, which was one of the partners of this year’s report, to conduct a second study later this year.
More study is needed either way, and not just in Portland: The more information we have about how extreme heat affects people who are trying to shelter from it, the better prepared we are to make policies that can mitigate it. Some activists, for example, are calling for cities to institute summer maximum heat thresholds similar to how many northeastern cities mandate minimum temperatures in the winter — something that the Arizona cities of Phoenix and Tempe have already implemented. But every city, and even every building in every city, is different, and data collection will be key to moving from a one-size-fits-all policy of air conditioning to more targeted, productive solutions that take into account the way people interact with the buildings they live in.
“I tend to think that often what we're doing is throwing lots of money at things that we intuitively believe will work,” Shandas told me. “But what we think works may not always be the thing that works well. People inhabit spaces in very different ways, and I think we need to get a better handle on designing for their behaviors instead of throwing a bunch of money at our assumptions.”
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On boasts and brags, clean power installations, and dirty air
Current conditions: Strong winds helped spark dozens of fires across parched Texas • India’s Himalayan state of Uttarakhand experienced a 600% rise in precipitation over 24 hours, which triggered a deadly avalanche • The world’s biggest iceberg, which has been drifting across the Southern Ocean for 5 years, has run aground.
President Trump addressed Congress last night in a wide-ranging speech boasting about the actions taken during his first five weeks in office. There were some familiar themes: He claimed to have “ended all of [former President] Biden’s environmental restrictions” (false) and the “insane electric vehicle mandate” (also false — no such thing has ever existed), and bragged about withdrawing from the Paris climate agreement (true). He also doubled down on his plan to boost U.S. fossil fuel production while spouting false statements about the Biden administration’s energy policies, and suggested that Japan and South Korea want to team up with the U.S. to build a “gigantic” natural gas pipeline in Alaska.
On the same day as the speech, new tariffs on imports from Canada, Mexico, and China came into effect, triggering retaliatory duties and causing stock markets to plunge. Experts are busy trying to figure out what it all means for American businesses and consumers. As Heatmap’s Robinson Meyer explained, the tariffs are likely to make electricity prices go up, raise construction costs, make gas more expensive at the pump, and make new cars costlier. Fossil fuel firms aren’t thrilled. The American Gas Association said the 10% tariff on Canadian natural gas “indicates potential impacts totaling at least $1.1 billion in additional costs to American consumers per year.” Chet Thompson, CEO of the American Fuel & Petrochemical Manufacturers, said that “imposing tariffs on energy, refined products, and petrochemical imports will not make us more energy secure or lower costs for consumers.”
Commerce Secretary Howard Lutnick has implied Trump might lift these tariffs as soon as today, but TBD.
The Trump administration has ended a program that monitored the air quality at more than 80 U.S. embassies and consulates around the world, citing “budget constraints.” The program started in 2008 with the U.S. embassy in Beijing and expanded from there. The data collected, which was posted on the AirNow website, has been used in academic studies and credited with helping reduce pollution levels in the host countries, leading to better health outcomes. This move “puts the health of foreign service officers at risk” and could hinder research and policy, Dan Westervelt, a research professor at Columbia University’s Lamont-Doherty Earth Observatory, toldThe New York Times.
Clean power installations soared in the fourth quarter of 2024, sending total operational capacity above and beyond the 300 gigawatt mark, according to a new report from the American Clean Power Association. “It took more than 20 years for the U.S. to install the first 100 GW of clean power, five years to install the next 100 GW, and three years to install the most recent 100 GW,” the report says. Here are some takeaways:
ACPA
China plans to ramp up its efforts to rein in emissions, expanding its emissions trading system beyond power plants to to include industries such as steel, aluminum, and cement, Premier Li Qiang said in a report this week. “Li also confirmed China intends to continue to play a key role in diplomacy on emissions reduction, as the U.S. retreats from international cooperation,” Bloombergreported. The country plans to roll out major climate projects such as offshore wind farms, “new energy bases” across its deserts, with a goal of reaching peak emissions before 2030. China is the world’s largest emitter of greenhouse gases, and while it has been rapidly expanding renewable power generation, it also struggles to wean itself off coal.
The Supreme Court yesterday watered down the Environmental Protection Agency’s authority to regulate water pollution, siding with the city of San Francisco in an unusual lawsuit pitting the liberal hub against the environmental authority. In a 5-4 decision, the justices said the agency had overstepped its authority under the Clean Water Act when it issued permitting for a San Francisco wastewater treatment plant that empties into the Pacific. The permit included provisions that would have made San Francisco authorities responsible for ensuring the water quality in the Pacific met EPA standards. Justice Samuel Alito essentially wrote that the permitting rules were too vague. “When a permit contains such requirements, a permittee that punctiliously follows every specific requirement in its permit may nevertheless face crushing penalties if the quality of the water in its receiving waters falls below the applicable standards,” Alito wrote. The ruling will make it harder for the EPA to limit water pollution. Next up on the SCOTUS docket: nuclear waste!
Bernard Looney, the former CEO of oil giant BP, is the new boss of an AI startup that tells businesses how to cut their emissions.
A conversation with Resources for the Future’s David Wear on the fires in the Carolinas and how the political environment could affect the future of forecasting.
The Wikipedia article for “wildfire” has 22 photographs, including those of incidents in Arizona, Utah, Washington, and California. But there is not a single picture of a fire in the American Southeast, despite researchers warning that the lower righthand quadrant of the country will face a “perfect storm” of fire conditions over the next 50 years.
In what is perhaps a grim premonition of what is to come, several major fires are burning across the Southeast now — including the nearly 600-acre Melrose Fire in Polk County, North Carolina, a little over 80 miles to the west of Charlotte, and the more than 2,000-acre Carolina Forest fire in Horry County, South Carolina. The region is also battling hundreds of smaller brush fires, the smoke from which David Wear — the land use, forestry, and agriculture program director at Resources for the Future — could see out his Raleigh-area window.
Wear is also the co-author of a study by RFF and the U.S. Forest Service that came out in late 2024 and singled out the Southeast as facing a “particularly worrisome” rise in wildfire risk over the next half-century. I spoke with him this week to learn more about why the Carolinas are burning and what the future of fire looks like for the region. Our conversation has been edited and condensed for clarity.
When discussing fires in the American West, we often talk about how historic suppression efforts are responsible for the megafires we see today. What was the historic fire regime like in the Southeast? What’s going on to make it a hot spot for wildfires?
First, there are the similarities. Both Western and Southeastern forests, especially pine forests, are fire-adapted systems; they need regular fires to maintain health. Anything that takes those forests out of balance is a problem, and fire suppression is an issue in the East and the West, and especially in the Southeast. But forests in the Southeast are the most heavily managed forests in the country — perhaps in the world. In many cases, they’re regularly burned; the South does more prescribed burning than the rest of the country combined. It’s a very, very common practice in this part of the world.
So we shouldn’t be surprised that there is fire in Southeastern forests. There have been big, episodic fires in the South, though they’re not as common. There was the fire in 2016 in East Tennessee, from the Smokies into Gatlinburg, with a number of fatalities and lots of structures damaged or destroyed. There have been big fire years in east and west Texas. And there have been big fire seasons in Florida, though it’s been a while.
How is population growth in the Southeast adding to the strain?
We’re accustomed to talking about the wildland-urban interface in the West, but it’s also a big issue in the Southeast. Some of our urban growth centers in the Southeast include the Raleigh-Durham area, where I live, and Atlanta, Nashville, and Florida. These are generally flat landscapes, as well as very heavily forested landscapes. As the population grows out of the city centers, they go into pine and mixed-pine hardwood forests that are fire-adapted ecosystems. Then you have interspersed communities with forest vegetation, and that’s a big issue.
I also read in your report that much of that land is privately owned, which makes management tricky.
Private ownership is about 89% of forests in the South. [Editor’s note: By comparison, only about a third of forests in the West are privately owned.] Even where you have public ownership, a lot of that is by the Department of Defense and concentrated in a couple of different areas in the Ozarks and southern Appalachians. Much of the landscape in the coastal plain and Piedmont — which is most of the South — is predominantly private ownership.
There’s a distinction to be made between commercial owners, like timber investment management companies or real estate investment trusts, who actively manage landscapes. With timber harvesting, there are a lot of risk mitigation activities and a lot of prescribed burning. But then you have over a million non-industrial private landowners with small holdings. If you’re trying to coordinate any kind of wildfire mitigation scheme using fuel treatments and the like, it requires some work.
Horry County, South Carolina, and Polk County, North Carolina, were not part of your paper’s list of counties vulnerable to wildfire. I’m curious if you think what we’re seeing now says something about the limits of the study and the data you had available, or if you have another takeaway about what’s going on.
Importantly, our study looked at long-term averages. Throughout the South, there is a fire regime, and in any given year, it is possible to have wildfires of consequence. I would point out that we were especially concerned this year because Hurricane Helene laid down an awful lot of trees and created a fuel load.
We’re also entering one of the two fire seasons in the South. Wildfire is most predominant in the spring and in the fall; it’s at those times when temperatures begin to rise but humidity remains low, and there are extended dry periods that allow the fuels to dry out. You have warm temperatures and wind in the spring, setting the stage for wildfire. Typically, that window will begin to close at the end of April because it’s pretty darn humid in the South at that point, and it’s much less likely that fuels will get dry enough to carry a fire.
The same thing happens in the fall: Temperatures may remain high, and if we don’t have a lot of precipitation and humidity — usually in October and into November — then you have the conditions right for fire. But as the climate shifts, we see the length of those seasons growing to the point where the fall is approaching the spring. Wildfires in January and February indicate that these two seasons are growing toward one another and providing a much longer season. Our paper showed that, when you account for climate change across all of those global climate models and representative concentration pathways, the windows for more wildfire activity and more intense wildfire activity are expanding.
Your paper cited wildfire risks across the Sun Belt. Today, the National Weather Service is warning of “potentially historic” fire conditions in central Texas. Can local emergency managers use your modeling to prepare for such situations?
Things like the year-to-year fire projections and the day-to-day forecasts best serve local emergency managers. Wildfire in the South is determined by the drying of fuels and temperature and humidity conditions, which vary daily. If we look over the last week, Saturday was beautiful in the Carolinas. It was sunny, in the 70s, dry, and a little windy. That was the day [hundreds of] fires started across the Southeast. And the next day, there were very few new fires. Mid-week projections of wildfire potential in the Southeast show that it’s really low, with the exception of Texas. It changes day to day, driven by fine-grain weather forecasts, and that gives emergency managers some insight into where they might want to pre-position crews or do pre-suppression activities.
What we’re doing with the modeling is asking, What is this going to look like in 50 years? The takeaway is that wildfire activity is going to remain strong and perhaps grow in the West, but the big structural change is really strong growth and active fire in the Southeast, where you have wildfire and wildlands proximal to millions of people and more vulnerable communities. It’s a fire regime that’s going to affect more people.
I also wanted to ask about the USDA Forest Service’s contributions to your paper. Do you think research like this could still happen today, given the Trump administration’s efforts to eliminate anything climate-related from the federal agenda?
I came to Resources for the Future six years ago after a long career with the Forest Service, so it’s hard for me to remain a dispassionate scientist here. I think we need to see how the dust settles. It’s hard to imagine a future where the agency and federal government do not have a high level of concern regarding fire — and I don’t think you can do any kind of effective planning, or thinking about the future, or targeting of activities without understanding how climate is likely to impact these disturbance regimes.
I don’t have the crystal ball that many people are seeking right now. We’ll have to wait to see. But our research demonstrates the vital role of understanding climate dynamics, and it shows how critical weather forecasts are for people with boots on the ground who are trying to stay ahead of disaster.
Editor’s note: This story has been updated to reflect that about a third of land in the West is privately owned, not publicly owned.
Rob and Jesse visit Intersolar and Energy Storage North America.
Longtime listeners of Shift Key will recognize the name Intersolar and Energy Storage North America, one of the country’s premier solar industry conferences. Shift Key was live at this year’s event, hosting a panel on the present and future of the solar industry featuring a pair of marquee panelists: Tom Starrs, currently the vice president for government and public affairs at EDP Renewables, North America, who has more than 30 years of experience in the renewables industry; and Maria Robinson, until recently the director of the Department of Energy’s Grid Deployment Office and now the president and CEO of the Interstate Renewable Energy Council. (Robinson is also a repeat Shift Key guest.)
On this week’s episode of Shift Key, Rob and Jesse talk with the panelists about the momentum propelling solar energy forward in the U.S. and whether the uncertainty created by the Trump administration could put a damper on that. Shift Key is hosted by Jesse Jenkins, a professor of energy systems engineering at Princeton University, and Robinson Meyer, Heatmap’s executive editor.
Subscribe to “Shift Key” and find this episode on Apple Podcasts, Spotify, Amazon, or wherever you get your podcasts.
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Here is an excerpt from our conversation:
Maria Robinson: I actually want to go back to the permitting piece because I think this is directly related to the conversation. I suspect everyone here has tried to permit at some point in time on federal lands and found that to be an incredibly overwhelming experience, right? When we talk about this — and my new bugaboo, for the rest of my life, is we cannot call it NEPA anymore. It is not just NEPA. It is also the Fish and Wildlife Section 7 piece, it is also working with your state historical preservation offices. There are so many other pieces than just NEPA that some of these energy permitting reform bills do not, will not actually solve some of the issues that folks are looking at.
Jesse Jenkins: They’re too narrow, yeah.
Robinson: They’re just far too narrow, associated with that. And I think that was one of the things that I was not allowed to say like four weeks ago but I can say now. That did not go far enough in —
Robinson Meyer: Do you think that friendlier lawmakers in Congress understand this distinction? Or is it all the focus is still on NEPA?
Robinson: I think all the focus is still on NEPA, and there has to be a little bit more of that conversation, right? It was fascinating to me: This weekend, the National Governors Association met in D.C., and they all agreed on this resolution about, we need to do energy permitting. And the truth of the matter is, I think, I’m sure for many of you who’ve tried to work with a state historical preservation office, that you’re actually butting up against a lack of capacity at the state level sometimes, as opposed to at the federal level.
So there needs to be that conversation that is not just all, if we suddenly make vast changes to NEPA, that everything in terms of investment is and infrastructure is going to move faster. And I think that that is something that, especially Republican lobbyists and members of Congress and members of the administration can get behind, is that sort of efficiency, right? Efficiency is the word of the moment.
Music for Shift Key is by Adam Kromelow.