Gobally, June 2019 was the hottest June on record, according to the National Oceanic and Atmospheric Administration, and the World Meteorological Organization believes this past July may have been the hottest month on record.
While daytime extremes have garnered widespread media attention, overnight low temperatures are rising faster than daytime highs, bringing additional health risks.
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The research and news organization Climate Central recently examined changes in average summer low temperatures around the country, finding a national increase of 1.8 degrees Fahrenheit since 1895, when records began.
Reno, Nevada, topped the list with an increase of 16.9 degrees during that period while Jacksonville and the state of Florida came in below the national average, both seeing about 1.5 degrees of warming - but most of that warming has happened since 1970.
“We are starting to see the nights warm more rapidly than the daytime hours are, and that's actually very consistent with what we know about climate change,” said Climate Central Meteorologist Sean Sublette. “This is warming that is independent of the sun.”
And these rising temperatures are being felt more in urban areas, where a phenomenon known as the urban heat island effect (UHI) occurs.
Cities tend to be hotter than surrounding areas because they have fewer shade-providing trees and a lot more heat-retaining materials and surfaces like asphalt. The extra heat that’s absorbed during the day is then re-radiated at night, keeping air temperatures in urban areas an average of 22 degrees warmer than the surrounding areas.
Warmer night temperatures can lead to various health risks. When temperatures don’t drop significantly overnight it doesn’t give people a chance to recover from extreme daytime heat, especially in areas where people aren’t used to extreme temperatures.
Health risks are higher for vulnerable populations like the sick, the elderly and lower-income communities that may not have access to or can’t afford air conditioning, which is becoming more expensive as temperatures rise.
“It's much different in Florida than it is in a hot place like Arizona, which we like to call having a dry heat,” said Sublette. “When it's a drier heat, it puts a little less stress on the air conditioner. High humidity, like we see in Florida, and high heat puts a lot more stress on an air conditioning unit. And that is really going to drive up your costs more.”
To help reduce energy costs and health risks in an environmentally friendly way, communities can adapt by doing things like planting trees and building green infrastructure while individuals can cool off by using fans with ice tanks instead of AC units. The most important thing to do, Sublette said, is to find ways, big and small, to reduce carbon emissions.