You’re out of free articles.
Log in
To continue reading, log in to your account.
Create a Free Account
To unlock more free articles, please create a free account.
Sign In or Create an Account.
By continuing, you agree to the Terms of Service and acknowledge our Privacy Policy
Welcome to Heatmap
Thank you for registering with Heatmap. Climate change is one of the greatest challenges of our lives, a force reshaping our economy, our politics, and our culture. We hope to be your trusted, friendly, and insightful guide to that transformation. Please enjoy your free articles. You can check your profile here .
subscribe to get Unlimited access
Offer for a Heatmap News Unlimited Access subscription; please note that your subscription will renew automatically unless you cancel prior to renewal. Cancellation takes effect at the end of your current billing period. We will let you know in advance of any price changes. Taxes may apply. Offer terms are subject to change.
Subscribe to get unlimited Access
Hey, you are out of free articles but you are only a few clicks away from full access. Subscribe below and take advantage of our introductory offer.
subscribe to get Unlimited access
Offer for a Heatmap News Unlimited Access subscription; please note that your subscription will renew automatically unless you cancel prior to renewal. Cancellation takes effect at the end of your current billing period. We will let you know in advance of any price changes. Taxes may apply. Offer terms are subject to change.
Create Your Account
Please Enter Your Password
Forgot your password?
Please enter the email address you use for your account so we can send you a link to reset your password:
As climate writers, my colleagues and I spend a lot of time telling readers that places are hot. The Arabian Peninsula? It’s hot. The Atlantic Ocean? It’s hot. The southern U.S. and northern Mexico? Hot and getting hotter.
But here’s a little secret: “Hot” doesn’t really mean … anything. The word is, of course, of critical importance when it comes to communicating that global temperatures are the highest they’ve been in 125,000 years because of greenhouse gases in the atmosphere, or for public health officials to anticipate and prevent deaths when the environment reaches the point where human bodies start malfunctioning. But when you hear it’s “100 degrees out,” what does that really tell you?
Beyond that you’re a fellow member of the Fahrenheit cult, the answer is: not a lot. Humans can “probably avoid overheating” in temperatures of 115 degrees — but only if they’re in a dry room with 10 percent relative humidity, wearing “minimal” clothing, and not moving, The New York Times reports. On the other hand, you have a high chance of life-threatening heat stroke when it’s a mere 90 degrees out … if the humidity is at 95%. Then there are all the variables in between: if there’s a breeze, if you’re pregnant, if you’re standing in the shade or the sun, if you’re a child, if you’re running a 10K or if you’re napping on your couch in front of a swamp cooler.
In order to better specify how hot “hot” is, a number of different equations and techniques have been developed around the world. In general, this math takes into account two main variables: temperature (the one we all use, also known as “dry bulb” or “ambient air temperature,” which is typically measured five feet above the ground in the shade) and relative humidity (the percentage of air saturated with water vapor, also known as the ugly cousin of the trendier dew point; notably Canada’s heat index equivalent, the Humidex, is calculated from the dew point rather than the relative humidity).
In events like the already deadly heat dome over the southern United States and northern Mexico this week, you typically hear oohing and ahhing about the “heat index,” which is sometimes also called the “apparent temperature,” “feels like temperature,” “humiture,” or, in AccuWeather-speak, the “RealFeel® temperature.”
But what does that mean and how is it calculated?
The heat index roughly approximates how hot it “actually feels.”
This is different than the given temperature on the thermometer because the amount of humidity in the air affects how efficiently sweat evaporates from our skin and in turn keeps us cool. The more humidity there is, the less efficiently our bodies can cool themselves, and the hotter we feel; in contrast, when the air is dry, it’s easier for our bodies to keep cool. Regrettably, this indeed means that insufferable Arizonans who say “it’s a dry heat!” have a point.
The heat index, then, tells you an estimate of the temperature it would have to be for your body to be similarly stressed in “normal” humidity conditions of around 20%. In New Orleans this week, for example, the temperature on the thermometer isn’t expected to be above 100°F, but because the humidity is so high, the heat toll on the body will be as if it were actually 115°F out in normal humidity.
Importantly, the heat index number is calculated as if you were standing in the shade. If you’re exposed to the sun at all, the “feels like” is, of course, actually higher — potentially as many as 15 degrees higher. Someone standing in the New Orleans sun this week might more realistically feel like they’re in 130-degree heat.
The heat index graph.NOAA
Here’s the catch, though: The heat index is “purely theoretical since the index can’t be measured and is highly subjective,” as meteorologist Chris Robbins explains. The calculations are all made under the assumption that you are a 5’7”, 147-pound healthy white man wearing short sleeves and pants, and walking in the shade at the speed of 3.1 mph while a 6-mph wind gently ruffles your hair.
Wait, what?
I’m glad you asked.
In 1979, a physicist named R. G. Steadman published a two-part paper delightfully titled “The Assessment of Sultriness.” In it, he observed that though many approaches to measuring “sultriness,” or the combined effects of temperature and humidity, can be taken, “it is best assessed in terms of its physiological effect on humans.” He then set out, with obsessive precision, to do so.
Steadman came up with a list of approximately 19 variables that contribute to the overall “feels like” temperature, including the surface area of an average human (who is assumed to be 1.7 meters tall and weigh 67 kilograms); their clothing cover (84%) and those clothes’ resistance to heat transfer (the shirt and pants are assumed to be 20% fiber and 80% air); the person’s core temperature (a healthy 98.6°F) and sweat rate (normal); the effective wind speed (5 knots); the person’s activity level (typical walking speed); and a whole lot more.
Here’s an example of what just one of those many equations looked like:
One of the many equations in “The Assessment of Sultriness: Part I,”R.G. Steadman
Needless to say, Steadman’s equations and tables weren’t exactly legible for a normal person — and additionally they made a whole lot of assumptions about who a “normal person” was — but Steadman was clearly onto something. Describing how humidity and temperature affected the human body was, at the very least, interesting and useful. How, then, to make it easier?
In 1990, the National Weather Service’s Lans P. Rothfusz used multiple regression analysis to simplify Steadman’s equations into a single handy formula while at the same time acknowledging that to do so required relying on assumptions about the kind of body that was experiencing the heat and the conditions surrounding him. Rothfusz, for example, used Steadman’s now-outdated calculations for the build of an average American man, who as of 2023 is 5’9” and weighs 198 pounds. This is important because, as math educator Stan Brown notes in a blog post, if you’re heavier than the 147 pounds assumed in the traditional heat index equation, then your “personal heat index” will technically be slightly hotter.
Rothfusz’s new equation looked like this:
Heat index = -42.379 + 2.04901523T + 10.14333127R - 0.22475541TR - 6.83783x10-3T 2 - 5.481717x10-2R 2 + 1.22874x10-3T 2R + 8.5282x10-4TR2 - 1.99x10-6T 2R 2
So much easier, right?
If your eyes didn’t totally glaze over, it actually sort of is — in the equation, T stands for the dry bulb temperature (in degrees Fahrenheit) and R stands for the relative humidity, and all you have to do is plug those puppies into the formula to get your heat index number. Or not: There are lots of online calculators that make doing this math as straightforward as just typing in the two numbers.
Because Rothfusz used multiple regression analysis, the heat index that is regularly cited by the government and media has a margin of error of +/- 1.3°F relative to a slightly more accurate, albeit hypothetical, heat index. Also of note: There are a bunch of different methods of calculating the heat index, but Rothfusz’s is the one used by the NWS and the basis for its extreme heat alerts. The AccuWeather “RealFeel,” meanwhile, has its own variables that it takes into account and that give it slightly different numbers.
Midday Wednesday in New Orleans, for example, when the ambient air temperature was 98°F, the relative humidity was 47%, and the heat index hovered around 108.9°F, AccuWeather recorded a RealFeel of 111°F and a RealFeel Shade of 104°F.
You might also be wondering at this point, as I did, that if Steadman at one time factored out all these variables individually, wouldn’t it be possible to write a simple computer program that is capable of personalizing the “feel like” temperature so they are closer to your own physical specifications? The answer is yes, although as Randy Au writes in his excellent Substack post on the heat index equation, no one has seemingly actually done this yet. Math nerds, your moment is now.
Because we’re Americans, it is important that we use the weirdest possible measurements at all times. This is probably why the heat index is commonly cited by our government, media, and meteorologists when communicating how hot it is outside.
But it gets weirder. Unlike the heat index, though, the “wet-bulb globe temperature” (sometimes abbreviated “WBGT”) is specifically designed to understand “heat-related stress on the human body at work (or play) in direct sunlight,” NWS explains. In a sense, the wet-bulb globe temperature measures what we experience after we’ve been cooled by sweat.
The Kansas State High School Activities Association thresholds for wet-bulb globe temperature.Weather.gov
The “bulb” we’re referring to here is the end of a mercury thermometer (not to be confused with a lightbulb or juvenile tulip). Natural wet-bulb temperature (which is slightly different from the WBGT, as I’ll explain in a moment) is measured by wrapping the bottom of a thermometer in a wet cloth and passing air over it. When the air is dry, it is by definition less saturated with water and therefore has more capacity for moisture. That means that under dry conditions, more water from the cloth around the bulb evaporates, which pulls more heat away from the bulb, dropping the temperature. This is the same reason why you feel cold when you get out of a shower or swimming pool. The drier the air, the colder the reading on the wet-bulb thermometer will be compared to the actual air temperature.
Wet bulb temperature - why & when is it used?www.youtube.com
If the air is humid, however, less water is able to evaporate from the wet cloth. When the relative humidity is at 100% — that is, the air is fully saturated with water — then the wet-bulb temperature and the normal dry-bulb temperature will be the same.
Because of this, the wet-bulb temperature is usually lower than the relative air temperature, which makes it a bit confusing when presented without context (a comfortable wet-bulb temperature at rest is around 70°F). Wet-bulb temperatures over just 80, though, can be very dangerous, especially for active people.
The WBGT is, like the heat index, an apparent temperature, or “feels like,” calculation; generally when you see wet-bulb temperatures being referred to, it is actually the WBGT that is being discussed. This is also the measurement that is preferred by the military, athletic organizations, road-race organizers, and the Occupational Safety and Health Administration because it helps you understand how, well, survivable the weather is, especially if you are moving.
Our bodies regulate temperature by sweating to shed heat, but sweat stops working “once the wet-bulb temperature passes 95°F,” explains Popular Science. “That’s because, in order to maintain a normal internal temperature, your skin has to stay at 95°F degrees or below.” Exposure to wet-bulb temperatures over 95°F can be fatal within just six hours. On Wednesday, when I was doing my readings of New Orleans, the wet-bulb temperature was around 88.5°F.
The WBGT is helpful because it takes the natural wet-bulb temperature reading a step further by factoring in considerations not only of temperature and humidity, but also wind speed, sun angle, and solar radiation (basically cloud cover). Calculating the WBGT involves taking a weighted average of the ambient, wet-bulb, and globe temperature readings, which together cover all these variables.
That formula looks like:
Wet-bulb globe temperature = 0.7Tw + 0.2Tg + 0.1Td
Tw is the natural wet-bulb temperature, Tg is the globe thermometer temperature (which measures solar radiation), and Td is the dry bulb temperature. By taking into account the sun angle, cloud cover, and wind, the WBGT gives a more nuanced read of how it feels to be a body outside — but without getting into the weeds with 19 different difficult-to-calculate variables like, ahem, someone we won’t further call out here.
Thankfully, there’s a calculator for the WBGT formula, although don’t bother entering all the info if you don’t have to — the NWS reports it nationally, too.
Log in
To continue reading, log in to your account.
Create a Free Account
To unlock more free articles, please create a free account.
What’s a big multinational like Microsoft to do when it wants to build with clean concrete?
Imagine you’re a corporate sustainability exec and your company is planning to build a new data center. You’ve managed to convince the higher-ups to pay extra to use low-carbon building materials, lest the project blow up your brand’s emissions goals. But when you meet with the general contractor hired for the job, they don’t actually know of any low-carbon concrete purveyors in the area. Concrete is a hyper-local industry by necessity — you can’t hold the stuff for more than 90 minutes or so before it hardens and becomes unusable.
So here you are, one of the few people with the power and budget to pay a premium for zero-emissions concrete — a product that must become the standard if we are to stop climate change — and you can’t even get your hands on it.
This is, more or less, the situation Microsoft has found itself in. Last year, the company’s indirect emissions rose 31%, primarily due to the construction of new data centers. Cement, the main ingredient in concrete, is one of the most carbon-intensive materials on the planet, responsible for 6% of global emissions, according to Rhodium Group’s estimate. Low-carbon cement exists and is starting to be manufactured at a small scale, but first movers with deep pockets like Microsoft can’t necessarily access it.
To solve this and help clean cement startups access a bigger pool of buyers, Microsoft is leading the development of a new market for low-carbon cement — what climate finance experts call a “book and claim” market.
The tech giant has signed a memorandum of understanding with Sublime Systems, a Massachusetts-based cement startup, saying that it will buy “environmental attribute certificates” from Sublime’s first commercial cement plants. Microsoft will “book” the environmental attributes — the greenness, for lack of a better word — of Sublime’s cement, and “claim” those attributes in its own emissions accounting.
Let’s get a collective groan out of the way. Yes, once again, the business community is proposing a sort of carbon credit system as the best way — possibly the only way — to scale climate solutions. These certificates, however, have at least one notable difference from the beleaguered carbon offsets you’ve likely heard so much about: They are tied to a physical product. Microsoft won’t be buying one ton of CO2 avoided or removed from the atmosphere and then subtracting that from its overall emissions ledger. It will be buying the rights to say that it used one ton of cement with a carbon intensity of zero (or whatever the carbon intensity of Sublime’s product ends up being). Instead of neutralizing its cement-related emissions by paying someone to plant trees, it’s doing so by enabling Sublime to sell its clean cement to local buyers at a competitive price.
“It tremendously simplifies our logistics,” Leah Ellis, the CEO and founder of Sublime Systems told me, by solving the unavoidable problem that at this early point in the company’s development, it would be impossible to deliver its cement to all the early adopters willing to pay extra for it. “We end up doing death by 1,000 pilots if we have to pilot here, there, everywhere. Being able to use the cement locally and have the carbon attribute be counted against Microsoft's Scope 3 emissions is a really innovative way to unstick this whole problem.”
That’s key. Scope 3 is a category of emissions that encompasses all the carbon that is related to a business but not directly produced by it. When Microsoft builds a data center, it has no direct control over the process used to make the cement that goes into the building. In theory, it does have the ability to say, “We want to use clean stuff, not dirty stuff.” But in reality, companies are struggling to effect change within their supply chains.
“The thing to understand right out the gate is that basically no major consumer-facing company that uses things like steel or aluminum or cement knows where their stuff actually comes from,” Stephen Lezak, a researcher focused on carbon markets at the University of California, Berkeley, as well as at Oxford University, told me. He thinks that’s going to change, and hopes that in 15 years we all look back on this fact in horror. But in the meantime, “the urgency of the climate crisis requires using high integrity tools that aren't ideal, but still preserve fundamental integrity from a carbon accounting perspective,” he said.
Microsoft, for its part, told me it sees this transaction as a near-term solution and “prioritizes buying and installing physical product first” i.e., before buying certificates, “where technical, geographical, and supply chain considerations align.”
Sublime is currently building its first commercial plant in Holyoke, Massachusetts, which will use its unique zero-emissions process to produce 30,000 tons of cement per year. The Department of Energy awarded the company an $87 million grant to fund the project earlier this year. Holcim and CRH, two of the largest building materials companies in the world, have also invested in Sublime and agreed to purchase most of the volume produced by the first plant.
Ellis hopes the deal with Microsoft will help attract additional investment and get the company through its “awkward teenage years.” Sublime needs to show investors that “people want this material, people will pay that green premium so that we can drive up the volume so that that premium goes away,” she said.
As with carbon offsets, there are still ways to game the system. Microsoft recently co-authored a report with the clean energy think tank RMI describing what a larger book and claim market for clean cement might look like and what questions need to be answered to ensure the market is credible. Until clean cement is just as cheap or cheaper than conventional cement, it’s pretty clear this kind of market will help reduce emissions. But should the environmental attributes be tied to cement, or to concrete? How should the carbon intensity be calculated? How will emissions be tracked and traced from the producer to the contractor to the building itself?
Perhaps the most critical question is how to avoid double-counting. If Microsoft is buying the right to say it used clean cement, what can the company that bought the actual cement say? Will it be able to brag that its building is green?
When I posed this question to Ellis, and Ben Skinner, a manager at RMI and one of the authors of the report, each gave me a version of the same answer: Yes and no.
Ellis launched into a passionate monologue about the concrete companies and contractors and structural engineers who should be celebrated for taking the risk of using a new material. “This problem of cement emissions is so intractable,” she said. “We need to make cement more visible. We need to talk about this more. We need more people to care. And so that physical embodiment, having it stamped ‘Sublime cement,’ and having a plaque that shows the public, hey, these are the emissions reduced by this thing you see here, you want to celebrate that physical embodiment.” At the end of all this, she added, “And by no means am I saying that you should double count.”
The suggestion is that it should be possible to separate carbon accounting and green marketing. If Microsoft has booked the green attributes of a delivery of cement, the contractors or building owners who used the physical stuff should not be able to claim they used clean cement on their emissions balance sheets, Skinner said. (What number they should use is a tricky question that will have to be solved.) But perhaps they still deserve some kind of recognition.
What kind of recognition, Lezak told me, is a gray area. “There's a really difficult part of this whole conversation, where you start anchored in material science and climate science and everything is really rigorous,” he said. “And at some point, the train sort of moves on to the political economy track, and it's really tough because you look for the same sort of black and white answers to these questions and they just don't show up.”
The details of the Microsoft deal and who can claim what are still being negotiated. At the same time, RMI and a new nonprofit called the Center for Green Market Activation have started work to stand up a larger book and claim market for cement. Their goal is to develop standards for how these certificates should be created, traded, and used so that companies that do not have the expertise or budget or resources that Microsoft has can access them. “We do think that it's possible to create a really high integrity system,” Skinner, told me.
Whether you like this idea or hate it, get ready to hear a lot more about it. The Center for Green Market Activation, which launched in June, is working to develop book and claim markets across a range of carbon intensive industries, including aviation, trucking, maritime shipping, and chemicals. There is one clear alternative to these paper-trading schemes — regulations that require companies to use more green materials over time. But proponents don’t see that happening anytime soon.
Lezak, though initially skeptical of these markets, has grown to support the idea. “There are people out there arguing that if you want to claim the emissions reduction in green steel, you need to make sure that the green steel actually shows up on your factory floor,” he said. “That's a beautiful idea, but you're talking about potentially pulling out the rug from billions of dollars of high integrity carbon finance.”
On the World Bank’s bad record keeping, Trump’s town hall, and sustainable aviation fuel
Current conditions: Parts of southwest France are flooded after heavy rains • Sydney’s Bondi Beach is closed because lumps of toxic tar are washing ashore • A winter storm warning is in effect for parts of Montana.
Nearly 40% of the climate finance funds that have been distributed by the World Bank over the last seven years are unaccounted for due to poor record keeping, according to a new report from Oxfam International. That’s up to $41 billion that is untraceable. “There is no clear public record showing where this money went or how it was used, which makes any assessment of its impacts impossible,” the report said. “It also remains unclear whether these funds were even spent on climate-related initiatives intended to help low- and middle-income countries protect people from the impacts of the climate crisis and invest in clean energy.”
The World Bank is the largest multilateral provider of climate finance, and has a goal of directing 45% of its total financing toward climate projects by 2025. The report noted that climate finance will be a key issue at the upcoming COP29, where countries will put forward a new global climate finance goal. “The lack of traceable spending could undermine trust in global climate finance efforts at this critical juncture,” Oxfam said.
During a town hall event hosted by Univision last night, Republican presidential candidate Donald Trump was asked by a veteran construction worker – who had seen first-hand “the devastating impacts of climate change” – if he still believed global warming was a “hoax.” In his response, Trump claimed to be an environmentalist, saying he’d won “many awards over the years” for the way he’d constructed his buildings, “the way I used the water, the sand, the mixing of the sand.” But, he said, “we can’t destroy our country” for the sake of saving the climate. He said the U.S. is competing against China, which “doesn’t spend anything on climate change.” According to the International Energy Agency, last year China alone accounted for one-third of the world’s clean energy investments.
Needless to say, Trump didn’t really answer the question about whether he thought climate change was real, but he did cast doubt on sea level rise and claimed “the real global warming we have to worry about is nuclear.”
I’ll just take this opportunity to remind you that Heatmap’s Jeva Lange put together an exhaustive fact-check on Trump’s climate and weather claims going back to 2001.
The Supreme Court yesterday allowed the Environmental Protection Agency to move forward with its rule restricting climate pollution from power plants, meaning that one of the Biden administration’s key climate policies can stay in place. For now. The high court’s decision will allow the EPA to defend the rule in a lower court over the next 10 months. Whether the Biden administration’s new attempt at regulating climate pollution will survive depends on the outcome of next month’s election. The Trump campaign has said that it will overturn the EPA’s new climate rules. Should Harris win, the rule will still have to survive the lower court challenge. That case is scheduled to be heard in front of the D.C. Circuit Court of Appeals this term.
Get Heatmap AM directly in your inbox every morning:
The Department of Energy yesterday announced its first two loans for sustainable aviation fuel. The roughly $3 billion in funding will go to two companies:
“As the aviation sector aims to meet its decarbonization goals, SAF will become increasingly vital,” the DOE said in a statement. “SAF is the only viable near-term option to decarbonize the airline industry.”
A Canadian court’s ruling on a climate lawsuit today could influence similar cases in Canada and other countries. Seven young people are suing the Ontario government over its emissions targets, which they say are inadequate and violate their human rights. If the case heads to Canada’s Supreme Court, and the plaintiffs win, that would “dramatically open the door to new litigation,” constitutional law expert Emmett Macfarlane toldReuters. “That would be explosive. It would have immediate ramifications for all governments.”
The University of California, San Diego, is the first major public university to require all its undergraduate students to complete a climate change course.
They may not survive a full challenge, though.
The Supreme Court allowed the Environmental Protection Agency to move forward with its rule restricting climate pollution from power plants on Wednesday, meaning that one of the Biden administration’s key climate policies can stay in place. For now.
The high court’s decision will allow the EPA to defend the rule in a lower court over the next 10 months. A group of power utilities, trade groups, and Republican-governed states are suing to block the greenhouse gas rule, arguing that it oversteps the EPA’s authority under the Clean Air Act.
The EPA’s new rules, which were finalized in April, would be the government’s first successful effort to regulate climate pollution from the power sector. The electricity industry is the second most-polluting sector in the American economy.
The Obama administration previously tried to regulate greenhouse gas pollution from the power sector. The Supreme Court blocked those rules from taking effect in 2016, before striking them down completely in 2022.
This time, the agency has written the rules within a framework laid out by the Supreme Court’s conservative majority in that ruling. In that now landmark case, the court ruled that the EPA could restrict greenhouse gas pollution from power plants only by requiring new technology, such as carbon capture equipment, to be installed at the plant itself. The agency couldn’t require utilities to stop burning fossil fuels and build more renewables.
In the near term, whether the Biden administration’s new attempt at regulating climate pollution will survive depends on the outcome of next month’s election. The Trump campaign has said that it will overturn the EPA’s new climate rules. During his first term, Donald Trump rolled back more than 100 environmental and climate protections.
Should Harris win, the rule will still have to survive the lower court challenge. That case is scheduled to be heard in front of the D.C. Circuit Court of Appeals this term.
“The high court made the right call,” Meredith Hankins, a senior attorney at the Natural Resources Defense Council, said in a statement. “Given its rulings in recent years undercutting environmental protections, the refusal of the majority on the Supreme Court to block this vital rule is a victory for common sense.”
Not all the news from the Supreme Court on Wednesday was good for climate advocates, though.
In the same decision that let the new rules stand, the high court’s conservative justices signaled that they might block the rules next year.
“In my view, the applicants have shown a strong likelihood of success on the merits as to at least some of their challenges” to the rule, Justice Brett Kavanaugh wrote in a short statement attached to the stay, which was cosigned by Justice Neil Gorsuch.
But because the rules don’t require utilities to start complying until next June, there was no reason to grant an emergency stay, the two justices added.
Justice Clarence Thomas would have gone further and stepped in to block the rules immediately. Justice Samuel Alito, another reliable conservative vote, did not participate in the deliberations.
That suggests that four justices could be ready to block the rules as soon as next year. They would need only one more vote — from Chief Justice John Roberts or Justice Amy Coney Barrett — to stay the protections from taking effect.
The statement didn’t provide any hints to what Roberts or Barrett are thinking.