Rich people live in cooler, greener city neighborhoods, while low-income people and people of color are suffering significantly higher summer temperatures in urban areas — a deadly environmental disparity that harms Black Americans more than any other group, according to a study published Tuesday. 

Across the U.S., the average Black person is exposed to urban summertime temperatures more than 3.12 degrees Celsius hotter than temperatures in non-built-up parts of their cities. White people were exposed to less than half that excess heat — 1.47 degrees Celsius, on average. The average person of color was exposed to higher urban heat than white people in 169 of the 175 largest cities in the U.S. 

This widespread evidence of environmental racism stunned one of the authors of the paper, published in Nature Communications.

"I expected there to be some evidence that people of color had worse exposure than whites, but I didn't expect it to be so pervasive," said Glenn Sheriff, an assistant professor at Arizona State University's School of Politics and Global Studies. "It wasn't just in the South, it wasn't just a handful of big cities — it was everywhere. Just the level of pervasiveness in this disparity was surprising to me."

Excessive heat causes around 1,500 deaths in the U.S. each year, a number likely to rise as human-induced climate change leads to more extreme weather events. Urban-planning choices, including decades-old choices about urban tree cover, not only affect quality of life for Black people and other people of color but also cause premature death, particularly among people over 65 and children under 5. Hispanic people had the second-worst temperatures, with a national average urban temperature 2.7 degrees Celsius higher than temperatures in the non-built-up parts of cities.

The new analysis, which is the first to cross-reference demographic data at the census-tract level and high-resolution satellite temperature data across the nation, found disparities between low-income people and rich people as well: People living below the poverty line were exposed to temperatures 2.7 degrees Celsius hotter, while people with incomes at least twice as high as the poverty line had the lowest levels of excess heat, only 1.8 degrees. But, notably, only 10% of people of color live below the poverty line, and income was clearly not the main factor in explaining racial differences in the built environment.

"I'm an economist," said Sheriff, the sole white author alongside three equally contributing authors of color. Knowing cooler neighborhoods are more desirable and thus likely to be more expensive, he said, "I would expect that the average person in poverty would face a higher temperature exposure than the average person of color. But we don't find that. In fact, the distribution of heat exposures for people of color is almost exactly the same as the distribution for people living below poverty, despite the fact that the average person of color lives above the poverty line."

Some of the worst cities — where people of color experienced a statistically significant temperature over 3 degrees Celsius higher than white people — were Providence, Rhode Island; Reading, Pennsylvania; and Bridgeport, Connecticut. New York City had a difference of 2.19 degrees Celsius, Los Angeles had a difference of 1.82 degrees and Boston had a difference of 2.6 degrees. The worst disparities were in the Northeast and the Upper Midwest, likely the result of tree cover; in arid areas especially, there was less tree cover overall, and therefore less disparity. 

The single city in which non-Hispanic white people had more exposure to higher temperatures was McAllen, Texas.

"This is something that's pervasive, and not just within a particular region or climate zone but across the entire country," Sheriff said. "The next question is to try to understand, what are the causal relationships? What is the root of this disparity?" 

He also noted that policymakers should involve local stakeholders and assess unintended consequences before showing up in Black neighborhoods with shovels and trees. "We need to figure out, if we have an urban forestry initiative, does it end up pricing people out?" he said. 

The paper, "Disproportionate exposure to urban heat island intensity across major US cities," published May 25 in Nature Communications, was authored by Angel Hsu, Yale-NUS College, University of North Carolina at Chapel Hill and Data-Driven EnviroLab; Glenn Sheriff, Arizona State University; Tirthankar Chakraborty, Data-Driven EnviroLab and Yale University; and Diego Manya, Yale University.