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Andrea Thompson: As you might have heard, heat records are breaking all around the world from the Mediterranean to South Asia. Most recently, records fell in the Pacific Northwest and western Canada. 

[Clip: Various newscasts]

Newscaster: Across British Columbia, residents are dealing with a record-breaking heat wave.

Newscaster: Seventeen temperature records fell on Saturday with heat advisories falling across much of Western Canada. 

Interviewee: This is not a usual May. This is not even an abnormally dry May. This is something exceptional.

Kelso Harper: A few places saw temperatures in the mid-90s. For context–that’s about 20 to 25 degrees Fahrenheit above normal.

Thompson: Today we’re talking about heat. It’s nearly summer in the Northern Hemisphere, and with climate change, today’s hot summers will be among the coolest of the rest of our lives.

Thompson: I’m Scientific American’s earth and environment editor, Andrea Thompson.

Harper: I’m Kelso Harper, a SciAm multimedia editor, and you’re listening to Science, Quickly.

[Clip: Show theme music]

Harper: So, Andrea, first things first. How does a heat wave even happen?

Thompson: Heat waves happen when a high pressure system parks itself over an area for several days. Under these systems, air sinks, which keeps clouds from forming. And if you don’t have clouds in the sky—that means the sun can really bake the surface. Imagine getting into your car after it’s been sitting in the sun, and you get the picture. 

Harper: Right, and this can be really dangerous. In June of 2021, a particularly strong heat wave in the same area contributed to hundreds of deaths. 

Thompson: With climate change, heat waves like this are happening more often, they’re lasting longer and they’re likely to become more intense as time goes on. 

Harper: And heat records are more likely to be broken and in some cases completely shattered. Normally, heat records are broken by a few tenths of a degree. But last week in Canada near Hudson Bay—which is still covered in winter ice—a heat record was broken by a huge 7 degrees Celsius, or more than 12 degrees Fahrenheit. The temperature shot up 40 degrees Fahrenheit over the average. 

Thompson: But a heat wave doesn’t have to set records to feel miserable. Especially in places like the Pacific Northwest, where air conditioning isn’t as prevalent and where people are less adjusted to heat. And at times of the year—like May—when people aren’t expecting them.

Harper: Heat waves are also particularly tough on the elderly, young children and people with health conditions like asthma or heart disease.

Thompson: And it’s not just the soaring high temperatures of the day that pose a problem. Higher nighttime temperatures mean people don’t have a chance to cool down, particularly if they lack air conditioning.

Harper: And humidity plays a role in our experience of heat, right?

Thompson: Yeah, as anyone who’s stepped outside on a summer day knows, high temperatures cause us to sweat. That’s actually the body’s natural cooling system, because the sweat cools our skin as it evaporates. But when the humidity is high, that evaporation slows down and can eventually stop.

Harper: And with global temperatures rising higher every year, it sounds like the heat waves and summers that are among the hottest in memory today are going to be left in the dust. 

Thompson: Yeah, the summer of 1998 was by far the hottest summer on record at the time, thanks to a blockbuster El Niño event, but it’s now the 10th hottest.

Harper: Speaking of El Niño, forecasters are expecting one to develop this year. Can you remind us what an El Niño actually is?

Thompson: An El Niño happens when ocean waters in the eastern part of the tropical Pacific are hotter than usual. The heat that releases into the atmosphere shifts around some of the big air circulation patterns that influence weather all over the world. That heat also amps up global temperatures.

Harper: And how likely is it that we’ll see one this year?

Thompson: There’s about a 90 percent chance right now, and it’s looking like it could be a fairly strong one, which would mean big weather impacts all over the world. 

Harper: What kind of weather impacts might it have?

Thompson: So, in some places like Indonesia, it actually is a lot drier than normal, and they end up with drought and sometimes wildfires that spew tons of smoke in the atmosphere. In other places, it can cause flooding because of higher-than-normal rains. And in the Atlantic Ocean, it actually tamps down on hurricane development, and so we tend to have quieter hurricane seasons when there’s an El Niño.

Harper: Wow, that’s really interesting. Okay, so not every summer is going to be a scorcher or hotter than the last one, but it’s pretty clear we’re going to have to adapt to having more hot weather.

Thompson: And it can seem like something we’re powerless to stop, but we can actually control just how hot the summers of the future are. The faster we bring down greenhouse gas emissions, the less roasting and deadly those future summers will be.

Harper: Local policy interventions can also help, like by creating more green spaces in cities or by painting building roofs white so they reflect more sunlight. 

Thompson: If you find yourself in a heat wave this summer and want to know how to keep cool, we have an FAQ linked in the show notes. It covers the difference between heat stroke and heat exhaustion, what to do if the power goes out and at-home heat remedies.

Personally, I’m a fan of a nice cold ice pack on the neck—and so is my dog.

Harper: Aww, that’s so sweet. Last summer I got by with lots of cold showers, frozen washcloths and occasionally sleeping in the living room next to the air conditioner.

Thompson: You’ve gotta do what you’ve gotta do to stay cool! 

[Clip: Show theme music]

Thompson: Thanks for listening to Scientific American’s Science, Quickly. The show is produced by Jeff DelViscio, Tulika Bose and Kelso Harper. It is edited by Alexa Lim and Elah Feder. Our music is by Dominic Smith.

Harper: If you liked this show, please consider leaving a rating or review. And check out ScientificAmerican.com for more in-depth news and features on all things earth and environment and everything else.

Thompson: For Science, Quickly, I’m Andrea Thompson.

Harper: I’m Kelso Harper.

Thompson: Until next time, stay cool!

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