sunrise over a smoggy city

The forecast said it would be 90 degrees. So why does your thermometer say it’s 100?

The weather forecast says it’s going to be hot. Air temperatures are projected to soar into the high 90s or even reach the 100s. But in some places on the ground, it can feel a lot hotter—like the inside of an oven.

That’s not your mind playing tricks on you. It actually is hotter in some neighborhoods than in others, even in the same region, says Brian Helmuth, a professor of marine and environmental sciences based at the Coastal Sustainability Institute at Northeastern’s campus in Nahant, Massachusetts.

As devastating and historic heat waves have been sweeping the nation this summer, the extreme heat has highlighted such divides. And those hotter areas tend to be the same places that experience many other kinds of inequality: largely non-white, less-affluent urban neighborhoods.

The temperature that you experience walking around outside is affected not just by the weather but by your environment, Helmuth says. As the sun beats down, pavement, buildings, and other constructed aspects of the urban environment heat up and radiate that warmth back out to heat the surrounding air (which is already very hot) even more.

“So if the air temperature today we’re measuring is 88 and you step outside on the pavement, it’s probably going to be more like 120” degrees Fahrenheit, Helmuth says.

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Marine and Environmental Sciences