MICHEL MARTIN, HOST:
We've been talking a lot about heat this week. Well, more hot weather is on the way. On top of all the record-breaking heat we've already seen this summer, NPR's Rebecca Hersher reports that climate change and El Nino are to blame.
REBECCA HERSHER, BYLINE: El Nino is the natural climate pattern that drives up global temperatures. It officially started in June. Now federal forecasters say they expect it to persist into 2024. Matthew Rosencrans is a meteorologist with the National Oceanic and Atmospheric Administration.
MATTHEW ROSENCRANS: We do expect the El Nino to continue through at least the Northern Hemisphere winter, and there's a 90% chance or greater of that happening.
HERSHER: So El Nino will stick around through next March. El Nino tends to mean hotter weather in the western part of the U.S., and we're already seeing that. In Phoenix, temperatures are lingering above 110 degrees, and nearly 400 daily maximum temperature records fell in the southern U.S. in June and the first half of July, most of them in Texas. John Nielsen-Gammon directs NOAA's regional office for the South.
JOHN NIELSEN-GAMMON: El Paso is now at 34 consecutive days over 100 degrees and counting.
HERSHER: And the heat isn't going to let up. Forecasters announced today that they expect above-average temperatures for the Southern and Western U.S. in the coming months. Here's the thing - the heat waves that already happened this summer actually make that future hot weather more likely because the heat transforms the land itself. Here's how - imagine sunlight hitting the land. If that land is moist, like wet soil, the energy from the sun causes that moisture to evaporate. But if there's not a lot of moisture, most of the energy will be absorbed by the land and make the land hotter. Think of the difference between the sun hitting a moist grassy area versus a dry road. The road will get much hotter. The grassy area will stay cooler, but eventually, it will dry out, too, and get hotter.
NIELSEN-GAMMON: So as things dry out, as you run out of water to evaporate, all of the energy is able to go into heating the ground, which then heats up the air above the ground.
HERSHER: Hot land radiates that heat into the air like a hot blacktop. On top of that, once the moisture has dried up, there's less water available to make clouds, which would then fall as rain, so the dry soil stays dry. That's called a feedback loop. Hot, dry weather causes more hot, dry weather.
NIELSEN-GAMMON: That feedback's been triggered by the heat wave we had in June. And so now that things are dry, they're more likely to stay dry and hot.
HERSHER: Such feedback loops are a hallmark of human-caused climate change because the whole planet is heating up. There's a way out, though. If humans stop emitting greenhouse gases, temperatures will stop rising.
Rebecca Hersher, NPR News.
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