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A summer school program in Roanoke, Virginia, could change the way people think about heat.
According to legend, the ghost of Lucy Addison still roams the halls of her namesake middle school in Roanoke, Virginia. She’s particularly fond of the basement, where the art and technology rooms are.
So when Brian Kreppeneck got a few thermal cameras for a summer program he was running this year, he knew exactly how he was going to teach his students how to use them: with a ghost hunt. He took them downstairs to the auditorium, shut off the lights, and had them train the cameras on things like the air-conditioning vents, a digital clock blinking in one corner, and the empty auditorium stage.
“And wouldn't you know it, as we're looking at the auditorium stage, a little mouse ran across the auditorium,” Kreppeneck, a science teacher at the school, told me. “They screamed and ran out, and that’s how they learned to use the thermal cameras.”
The cameras had a use beyond ghost-hunting and scaring schoolchildren (and mice): The students were going to use them to measure temperatures in and around their school. Over the course of a week, they pointed the cameras at all kinds of things in the world around them, from basketball courts baking in the sun to the shady ground underneath trees. They also clipped sensors to their shoes, which measured ambient temperatures as the kids went about their days. But that was just the beginning.
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“We wanted to develop a curriculum where students learn both about the problem of urban heat, and then also are able to connect that with potential solutions that come from urban planning,” said Theodore Lim, assistant professor of urban affairs and planning at Virginia Tech and the designer of the summer program. “We want them to feel like there are things that [they] could do in [their] own neighborhoods to help mitigate some of those temperatures.”
Urban heat is a longstanding, intractable problem. Study after study has shown that cities are noticeably hotter than surrounding rural areas; this is called the Urban Heat Island effect. Many studies have also shown that the hottest parts of most cities tend to be the areas that house lower-income communities and communities of color, thanks to a dearth of vegetation, tightly packed buildings, and an overabundance of construction materials that radiate heat like concrete. Richer neighborhoods, meanwhile, tend to be lusher, with more space between buildings and, often, building materials like wood or brick that do a better job of dissipating heat.
But understanding just how the built environment affects heat is pretty hard. Meteorologists and weather apps tend to draw data from sensors at airports, which can’t give us any insight into the contours of heat within specific neighborhoods. The numbers we see on our phones often don’t reflect the temperatures we feel; a neighborhood by a river or a park, for example, would be much cooler than a neighborhood with high concentrations of concrete and asphalt, yet residents in both places would see the same temperature in their apps or on TV.
After a week of collecting data with another teacher, the middle-schoolers came back to Kreppeneck’s classroom to figure out what all the numbers had to say. Put together, the data from the thermal cameras and the shoe sensors created something few of us get to see: a personalized look at how the built world around them shaped the way heat worked in their lives. As Lim and Kreppeneck expected, the temperatures the kids experienced were often higher than the temperatures measured by the sensors at a nearby airport, sometimes by as much as 30 degrees Fahrenheit:
Temperatures collected by sensors on students’ sneakers compared to temperature recorded at a nearby weather station. Courtesy Theodore Lim
Each colored line represents the data from a student at one of the five schools that participated, while the black line represents the temperature reported by the weather station at a nearby airport. If we follow a few of the blue lines, which represent students from Addison middle school — the one with the ghost — we see some of their personal temperatures spiking high above the black line. This could be for a few reasons: maybe they’re playing basketball on a concrete court, or eating lunch outside, or walking around a neighborhood with few trees.
But on each day, when the black line is at its peak, we see almost all of the students’ temperatures dip far below it. That was when the kids were cooling off indoors, often in air-conditioned buildings. As day turns to night, we see temperatures at the weather station dip below what some of the kids experienced indoors. By the next morning, as the kids start going about their days, their lines spike above the weather station again.
“Before they did this activity, if you asked one of these middle school kids if humans can control the temperature outside, they’d say no way,” Lim said. “But then they start to make these correlations: Humans make decisions about where to plant trees, or where to build parking lots, or what color different surfaces should be. And so we kind of do control the outdoor temperature.”
This kind of realization also shifts heat away from being a personal issue that can be solved by, say, drinking water or cranking the air conditioner, to a systemic one. There’s something kind of freeing about this: Lim said that instead of being ashamed that their families might not be able to afford air conditioning, the students came to recognize that their neighborhoods were historically hotter because of decisions made by other people. Northeast and Southeast Roanoke, for example, both saw higher temperatures than the Northwest and Southwest quadrants, and the entire city was significantly hotter than the rest of Roanoke County:
Temperatures recorded in each quadrant over the course of the summer program. The bars show the range, while the boxes are the average. Courtesy Theodore Lim.
Armed with their temperature data, the students spent the second week of their summer program in Kreppeneck’s class learning about urban planning and mapping out ways their own neighborhoods could be redesigned to mitigate heat.
“As science teachers, we’ve always struggled to make the connection between science in the classroom and home,” Kreppeneck told me. “There’s always been some sort of a wall there, where the kids just think science takes place in the classroom. But giving them a real-world project made these concepts transcend the classroom.”
Kreppeneck also talked to his students about activism and advocating for change. This was the idea of Virginia Tech’s Lim; activism gives the kids a sense of agency over their built environment, and it also encourages them to start conversations with the adults in their lives who previously might not have paid much attention to climate change, whether due to a lack of information or the impression that it didn’t impact them. But climate change continues to push global temperatures higher — this September was the hottest on record — and the effect of climate change on heat is becoming increasingly harder to ignore. Creating policy to deal with those changes, however, is a difficult task.
“In Roanoke, as is probably the case in many cities, there's kind of a lot of contention between the government and some of these more vulnerable communities because of the history of urban renewal,” Lim said.
As Martha Park writes in a beautiful illustrated history for Bloomberg, northeast Roanoke was a thriving home for black and immigrant residents prior to urban renewal, a policy James Baldwin once called “negro removal.” Then, in 1955, the city declared the area “blighted,” seized the entire neighborhood through eminent domain, burned the buildings to the ground, and even exhumed nearly a thousand bodies from the local cemetery, dumping them in a mass grave outside town. Today, the area is mostly pavement and industrial parks.
“There’s a lot of mistrust on both sides,” Lim told me. “I’ve found that using youth-based community science is a relatively uncontroversial way of getting at some issues that actually do have very deep systemic causes.”
This was the third year Lim ran his program in Roanoke. In earlier years, Lim ran the program by himself at just one of the schools; this summer’s group, consisting of 130 students from all five Roanoke middle schools over the course of six weeks, was by far the largest, and Kreppeneck and another teacher took over most of the day-to-day. Going forward, Lim hopes it’ll turn into something more than a middle-school summer program; community leaders are talking about putting together a climate action plan for the city, and he’s exploring the possibility of creating programs at local high schools and churches that build on the middle school curriculum. The idea is to get the message about heat, and the solutions for it, out into the community in as many ways as possible.
Kreppeneck’s already planning on incorporating urban heat into his syllabus for the spring semester, expanding the two-week summer program into something that the students can engage with on a deeper level.
“My hope is that the kids will start talking about it, and start taking ownership,” Kreppeneck said. “Watching the looks on their faces, watching how the wheels started turning as to how they would change their neighborhood, it was very rewarding. If they believe in something, they can make change. It starts with them.”
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On Alaska’s permitting overhaul, HALEU winners, and Heatmap’s Climate 101
Current conditions: Kansas, Oklahoma, and Arkansas brace for up to a foot of rain • Tropical Storm Juliette, still located well west of Mexico, is moving northward and bringing rain to parts of Southern California • Heat and dryness are raising the risk of wildfire in South Africa.
The Trump administration has started the process to roll back logging protections from more than 44 million acres of national forest land. On Wednesday, U.S. Secretary of Agriculture Brooke Rollins proposed undoing a 25-year-old rule that banned building roads or harvesting timber on federally controlled forest land, much of which is located in Alaska. “Today marks a critical step forward in President Trump’s commitment to restoring local decision-making to federal land managers to empower them to do what’s necessary to protect America’s forests and communities from devastating destruction from fires,” Rollins said in a statement. “This administration is dedicated to removing burdensome, outdated, one-size-fits-all regulations that not only put people and livelihoods at risk but also stifle economic growth in rural America.”
Environmental groups slammed the proposal for jeopardizing wildlife habitats and putting waterways at risk. “Communities depend on clear water filtered by roadless areas, animals depend on the unfragmented habitat that can only exist where there are no roads, and anglers depend on clean water in the streams where trout and salmon swim,” Ellen Montgomery, the director of Environment America’s great outdoors campaign, said in a press release. “We cannot let these essential forests be carved up by roads, obliterated by chainsaws, and contaminated by mines.”
Heatmap’s new Climate 101 series aims, as Heatmap deputy editor Jillian Goodman explained, to be “a primer on some of the key technologies of the energy transition.” That includes “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.”
This might be especially helpful for those still trying to find their way into the climate conversation, but we hope there’s something here for everyone. For instance, did you know that contemporary readers might have understood Don Quixote’s “tilting at windmills” to be an expression of NIMBYism? Well, now you do!
The federal Permitting Council signed a first-of-a-kind memorandum of understanding to work together with Alaska’s government to streamline permitting on critical infrastructure projects across the state. First established in 2015, the agency was designed to improve transparency and speed up the greenlighting of infrastructure approvals. But it had yet to forge such a close pact with an individual state. “Our team is ready to work with Governor Dunleavy to bring Alaska back into the energy spotlight, ending the neglect of the Biden Administration and bringing Alaska’s incredible natural resources to the rest of the world,” Emily Domenech, the Permitting Council’s executive director, said in a statement.
Domenech — a former staffer for House Speakers Kevin McCarthy and Mike Johnson who went on to serve as a senior vice president at Boundary Stone, a firm founded by alumni of the Obama-era Department of Energy — acted as something of a Republican sage for the clean energy industry. In an interview with Heatmap’s Matthew Zeitlin after last November’s election, she urged the industry to forge closer relationships with members of the current congressional majority. “If you ask Republicans to be for or against the IRA as a whole, they’ll be against it,” Domenech said, “But Republicans think about energy as a regional issue. So instead of forcing this one size fits all approach, IRA advocates would be smart to give people room to support only the policies that make the most sense for their state or region.”
The Department of Energy selected another three companies to receive a special kind of nuclear fuel from its growing stockpile. HALEU — pronounced HAY-loo, an acronym for high assay low enriched uranium — is a reactor fuel enriched up to four times as much as traditional reactor fuel. The fuel is needed for all kinds of novel reactor designs, particularly those that use coolants other than water. Until recently, however, Russia’s state-owned Rosatom had enjoyed a virtual monopoly over its global supply. The Biden administration set aside billions for HALEU production. In April, the Trump administration selected five companies to receive some of the government-procured supply, including Westinghouse, Bill Gates’ TerraPower, and the Google-backed Kairos Power. Now the agency has picked another three:
Two firefighters battling the Bear Gulch fire on Washington’s Olympic Peninsula were arrested by federal law enforcement Wednesday. The reason for the arrests is unclear, according to the Seattle Times. Over three hours, federal agents from Border Patrol carried out an “operation on the fire,” demanding identification from members of two private contractor crews who were among the 400 firefighters battling Washington state’s largest active blaze. The Incident Management Team from the National Interagency Fire Center suggested that the action did not interfere with the efforts to tamp down the flames.
The American West is primed for wildfires right now. Following a lull in June and July, Heatmap’s Jeva Lange wrote that “the forecast for the Pacific Northwest for ‘Dirty August’ and ‘Snaptember,’ historically the two worst months of the year in the region for wildfires,” was full of warning signs, including low precipitation and abnormally high temperatures.
Living, gnawing weedwackers.Vesper Energy
The 1.36 million solar panels at Vesper Energy’s Hornet Solar farm in Swisher County, Texas, one of the United States' largest single-phase solar projects, were overgrown with vegetation. So naturally, the company brought in sheep. More than 2,000 white, wooly ovines arrived this month and were allowed to roam the facility’s six square miles. “As Texas continues to lead the nation in solar energy growth, solar grazing highlights how innovation can support rural economies, preserve farmland, and strengthen the state’s reliable energy future,” Vesper said.
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.