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June 24, 2025—How hot nights kill, whales are using tools, and the Psyche spacecraft is moving again. —Andrea Gawrylewski, Chief Newsletter Editor | | Artist rendering of the Psyche spacecraft in orbit around its namesake asteroid. NASA | | The central and eastern United States are in the middle of an extreme heat wave. Over the weekend an oppressive "heat dome" built up over the Midwest and slowly migrated eastward. Average global temperatures are climbing, and heat waves like these are becoming more frequent and severe, no matter where on the planet. Perhaps the most deadly outcome of these trends? Hot nights. When it stays hot after the sun goes down, more people die than typically would otherwise. Emergency room visits and hospital admissions go up. Premature births increase. Sleep and mental health suffer.
How it works: "If it doesn't cool down at night, then your core body temperature can't really get back to what is normal for you," says Kristie Ebi an epidemiologist at the University of Washington. "You're starting the next morning with a higher baseline." Death rates start to increase after about 24 hours during heat waves. "It's not the instantaneous exposure; it's the buildup over the course of a day, not getting relief at night. That starts affecting the cells and organs," Ebi says. What can be done: Immerse hands and feet in cool water—not icy cold. It will trigger a response from special types of blood vessels that release internal heat to the surface, where it can dissipate fast. The method is used regularly by the military. If you can, focus air conditioning on the bedroom; hotter nights make it difficult to sleep, impairing immune system function. More on extreme heat: | | Orcas seen massaging each other with kelp. Center for Whale Research, NMFS/NOAA permit 27038 | | Marine researchers watched drone footage from more than 100 feet above the ocean in the Pacific Northwest. Dozens of times they saw orcas (killer whales) yank out sections of the stem of bull kelp, a giant seaweed that forms vast underwater forests in coastal waters. The texture of this stem, called a stipe, is firm but springy—kind of like a foam roller. The orcas would place the bull kelp stipe on their faces and nuzzle against another killer whale—often a close family member or similarly-aged whale. The two would keep the kelp pressed between their bodies as they wiggled against each other for up to 12 minutes at a time.
Why this is interesting: The scientists suspect the orcas' kelp ritual may be a kind of skincare–the massages may have an exfoliating effect. Whales are known to play with kelp often (by carrying it around on their foreheads), but this kelp scrub routine is taken up by whales of all ages, and there's some evidence that orcas with flakier skin do it more. What the experts say: The observations are "convincing evidence of tool use" in orcas, says Janet Mann, a behavioral ecologist at Georgetown University. Most observations of tool-use have been in land-dwelling animals (like primates and some birds). Marine animals are streamlined for swimming and don't have appendages useful for grasping tools. | | | | |
- The world is projected to add another four billion air conditioning units by 2050. If those units are powered by fossil fuels—and in areas of highest growth, including India and Indonesia, they usually are—the increase will have substantial impacts on global greenhouse gas emissions, write a group of energy researchers and policy analysts. "Manufacturers and governments must... innovate to develop affordable and efficient AC technology using refrigerants with lower climate impact," they say. | 5 min read
| | Is there anything worse than trying to sleep in a hot room? A fan helps, but the night feels longer and less restful. What are your tips for keeping cool at night? | | —Andrea Gawrylewski, Chief Newsletter Editor | | | | |
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