If you live in South Florida for long, you quickly learn a sweaty lesson about weather: It’s not the heat, it’s the humidity.
And, as you might suspect stepping outside just about any sticky summer morning, the humidity is getting worse. Along with pushing air temperatures higher, scientists say climate change is also raising the dew point in Miami, Fort Lauderdale and the rest of region — meaning the air holds more moisture. And you feel hotter.
“It’s a double whammy effect from a positive feedback loop,” said Nkosi Muse, a doctoral student at the University of Miami’s Rosentiel School of Marine, Atmospheric and Earth Sciences.
Muse is currently working on a research paper looking at how increasing moisture in the air from rising global temperatures is limiting nightly cooling effects at the surface. So, basically, evenings don’t get as cool and each morning starts out hotter.
“As the temperature gets higher the humidity gets higher, it’s going to make it worse twofold,” Muse said in an interview with the Miami Herald.
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Rising temperatures have gotten a lot of attention over the last few years as weather forecasters in South Florida adopted new standards for extreme heat warnings based on the “feels like” temperature, a heat index that includes temperature and humidity. The impact of climate change has been felt in earlier than ever heat warnings and 46 days of heat index topping 100 degrees, a record set last summer.
The second critical part of the heat index, humidity levels dictated by dew points, haven’t been as much a part of the climate discussion.
But Brian McNoldy, a meteorologist also based at UM’s Rosentiel School, mapped the two parts of the index over the last 76 years. He found they’re both climbing, the dew point just a bit more slowly. Within the last decade at the Miami airport, McNoldy found there has been a .26 degree trend upwards in dew point. Air temperature increased by .41 degrees. The heat index, the combo of both, increased .59 degrees.
Humidity is why medical experts say that South Florida’s climate can be harder on the health and body than a dry climate like Arizona, where a 90 degree temperature doesn’t feel all that oppressive. Sweat is supposed to cool us off when it evaporates from our skin. But when it’s extremely humid, the sweat sticks and the body can’t cool itself off as well, raising the risks of heat exhaustion or stroke.
Typically, air temperature rises throughout the day and peaks in the afternoon. But on a Miami summer night, the air temperature might drop to the low 80s but humidity and the amount of water in the air doesn’t change as much, Muse said. There can be another factor adding to the mix. Surface temperatures in the city, elevated by concrete that slowly releases heat in the evening, remain higher than in past.
“The more heat we add to the environment, the more that greenhouse effect gets stronger,” Muse said.
This story was produced in partnership with the Florida Climate Reporting Network, a multi-newsroom initiative formed to cover the impacts of climate change in the state.
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