Intense heat wave takes aim at Northeast U.S.

The latest heat wave that has been broiling the Western United States over the last few days has made its way to New York City and other major urban centers in the Northeast such as Boston and Philadelphia.

More than 82 million Americans across the country live in areas placed under a National Weather Service heat alert on Friday, and temperatures are expected to rise even higher across the Northeast over the weekend. High temperatures are expected to reach 93 degrees Fahrenheit in New York City and 97°F in Philadelphia on Friday and climb to 98°F in New York and 99°F in Philadelphia on Sunday.

A blistering heat wave is spreading across the U.S., with temperatures reaching well above 100 degrees in many regions
A heat wave is spreading across the U.S., with temperatures reaching well above 100 degrees in many regions. (Lokman Vural Elibol/Anadolu Agency via Getty Images)

Extreme heat is becoming more prevalent as a result of climate change, and it can be particularly challenging for older cities, which often have infrastructure that lacks air conditioning and are home to populations of poorer residents. According to the Environmental Protection Agency, an “urban heat island” effect raises temperatures several degrees above nearby rural areas because “buildings, roads, and other infrastructure absorb and re-emit the sun’s heat more than natural landscapes such as forests.” This phenomenon tends to be most pronounced in lower-income neighborhoods, which on average have less tree cover.

While more than 90% of New York City residents have air conditioning, access is uneven. In some of the city’s lower-income neighborhoods, more than 20% lack air conditioning.

Exposure to extreme heat can be deadly. More than 2,000 people in Spain and Portugal died from heat-related causes during a European heat wave in the last week.

The Northeast is also a relatively wet and humid region, and the heat index — a metric that adds humidity and heat to measure what the weather actually feels like — is surging past 100. In New York, it’s expected to measure 104 degrees on Sunday.

Cities including Boston have declared heat emergencies in anticipation of the heat wave and have opened cooling centers for residents.

“It is important that New Yorkers understand the potential dangers of extreme heat,” said New York City Emergency Management Commissioner Zach Iscol. “Remember to stay hydrated, and if you are venturing outdoors, avoid strenuous activity and wear lightweight clothing.”

Visitors in an interactive art installation,
Visitors cool off at Rockefeller Center in New York City. (Victor J. Blue/Bloomberg via Getty Images)

Scientists say it’s possible that climate models may have underestimated the frequency and duration of heat waves.

“There are a couple of kinds of processes that appear to be unfolding in the real world that the models may or may not really have a good handle on,” UCLA climate scientist Daniel Swain told Yahoo News.

“A lot of the really extreme heat waves that we’ve seen in recent years are these nonlinear, self-reinforcing, vicious-cycle feedback processes between the atmosphere and the land surface,” Swain said.

Extreme heat at the beginning of a heat wave quickly evaporates water from the plants on the Earth’s surface.

“Eventually you start to evaporate most of the water out of the soil and out of the landscape, so there’s less water available during later parts of the heat wave to evaporate in the atmosphere,” Swain explained. “Once you no longer have water to evaporate, a greater fraction of the sun’s energy goes into heating the ground and then the atmosphere above it. So, all of a sudden, the same amount of solar energy input at the end of a prolonged heat wave is creating more temperature increase than the first part of the heat wave. So you can see that if we’re getting more frequent and more intense heat waves, that can sort of be a self-reinforcing process, where the more intense heat wave evaporates more water out of the soil, which makes it hotter by the end of the heat wave. So if you initially say that climate change made the heat wave two or three degrees hotter, it might be that after you account for that feedback process, maybe it was more like six or seven degrees hotter. And all of a sudden, that’s a pretty large number.”


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