A New Way to Talk About Heat

Last month was not only the hottest May on record, it was the 12th month in a row to earn such a distinction. But was it “stickier”?

A study published in May in The Journal of Atmospheric Sciences proposes a new term to measure heat, one that may feel familiar: “stickiness.” Catherine Ivanovich, a climate scientist and Ph.D. candidate at Columbia University and lead author of the study, says that this new stickiness calculation combines several measurements of humidity and temperature. The goal is to determine which factor has the bigger influence on a hot day, the temperature measured by a thermometer or the moisture present in the air.

As climate scientists, meteorologists and public health officials grapple with record-breaking temperatures, they’re also exploring new ways of measuring extreme heat and new ways of communicating its risks.

We know that climate change increases the frequency, intensity and longevity of heat waves. And extreme heat is often striking earlier in the year.

On Sunday, at a rally for former President Donald Trump in Las Vegas, nearly 100 people crowded into cooling tents, sheltering from triple-digit temperatures, and six were taken to a local hospital, according to the Clark County fire department. Similar scenes have been playing out in heat waves across India, in Mexico and throughout the Western United States.

Isolating the geographic and atmospheric factors that contribute to different types of heat is important because not all heat is created equal. In arid climates, like the Southwest United States, dry heat allows for more perspiration, which helps cool the body. In more humid climates, like the Southeast, where more moisture crowds into the air particles, it’s harder for sweat to evaporate, which makes it harder to cool off.

The heat index, which is humidity combined with air temperature, gives us a good idea of what the air feels like outside. But a new stickiness measure could be even more specific. For example, it could help us determine how much of today’s expected high of 97 degrees Fahrenheit in Reno, Nev., is influenced by temperature and how much is influenced by humidity.

The composition of heat matters because extreme humid heat tends to be more dangerous than extreme dry heat, Ivanovich said. “Extreme humid heat is a local phenomenon that needs a personalized or localized way for addressing it,” she said. “It’s not one-size fits all.”

Right now, stickiness is a technical term, but in time, Ivanovich said it could help public health officials be better prepared to keep their communities cool.

The National Weather Service is also rethinking how it talks about heat. In April, in collaboration with the Centers for Disease Control and Prevention, it launched a new tool called HeatRisk. Users can search a map of the contiguous United States, or input their town or address to figure out their level of threat, ranging between one (little to no risk) and four (extreme risk).

The new N.W.S. system considers three factors. First, it tracks how unusual the heat is for the time of year, because hot days in, say, May are often harder on your body than when you’re acclimated to heat in July. It also accounts for the duration of the heat wave, as longer heat waves tend to create more public health problems, and it incorporates how the C.D.C. evaluates a given day’s heat-related hazards.

For example, if you’re in Atlanta with a high of 86 degrees Fahrenheit, today’s heat risk is “minor,” and is distinguished as a yellow level one on HeatRisk. But on Saturday, a high of 98 degrees means the heat risk is “major,” or a bright red level three. That kind of heat could affect anyone without air-conditioning or access to a cooling center, and those without adequate hydration, especially people working in heat-sensitive industries like farm or municipal workers.

Jessica Lee, public program coordinator at the National Weather Service, said HeatRisk is a first-of-its-kind program that combines both weather and C.D.C. health guidance. “It combines both aspects to provide personal, localized information,” Lee said. “It’s important to remember that heat is the number one weather related killer in the U.S. No one is immune to the impacts of heat.”

Bill Gates’ big bet on U.S. nuclear

A new generation of American nuclear plants is taking shape outside a coal town in southwest Wyoming. Workers began construction on Tuesday on a novel type of nuclear reactor meant to be smaller and cheaper than the hulking reactors of old and designed to produce electricity without the carbon dioxide that is rapidly heating the planet.

The reactor being built by TerraPower, a start-up, won’t be finished until 2030 at the earliest and faces daunting obstacles. The Nuclear Regulatory Commission hasn’t yet approved the design, and the company will have to overcome the inevitable delays and cost overruns that have doomed countless nuclear projects before.

What TerraPower does have, however, is an influential and deep-pocketed founder. Bill Gates, currently ranked as the seventh-richest person in the world, has poured more than $1 billion of his fortune into TerraPower, an amount that he expects to increase. — Brad Plumer

Read more about TerraPower’s nuclear projects.