NEW YORK (AP) — Ruben Berrios knows the scorching truth: When it comes to extreme heat, where you live can be a matter of life and death.

The 66-year-old lives in Mott Haven, a low-income neighborhood in New York’s South Bronx, where more than 90 percent of residents are Latino or Black. Every summer, the South Bronx becomes one of the hottest parts of the city, with temperatures 8 degrees (4.5 degrees Celsius) higher than on the Upper West and East sides — lusher, majority-white neighborhoods less than a mile away.

The heat isn’t just uncomfortable. It’s the top cause of weather-related fatalities nationwide, quietly killing an average of 350 New Yorkers each year, according to a city mortality report. As he took a break from his pool game at an apartment complex and older adult community center that serves as a designated cooling space, Berrios recalled a recent heat wave: “I lost two persons. They were close to me.”

Tens of millions of Americans are facing major heat waves, with temperatures consistently exceeding 90 degrees (32 degrees Celsius). But in big cities, the heat hits hardest for people of color and low-income residents. In New York, Black residents die from heat stress at double the rate of white residents.

“Only a quarter of New York City’s population is African American, but half of the deaths from heat are African Americans,” said Bill Ulfelder, executive director of the Nature Conservancy in New York. “So there is something wildly disproportionate.”

Mortality records from cities across the country have shown that heat kills along socioeconomic and racial lines.

In 1995, a deadly heat wave killed 739 people in Chicago. Most of the victims were poor, elderly and Black. Last year, Black people made up 11 percent of heat-related fatalities in Maricopa County, Arizona, which includes Phoenix, despite the fact that Black residents are just 6.8 percent of the county population.

During heat waves in Memphis, Tennessee, in the 1960s and 1980s, “there were people who were too poor to turn on their air conditioning" and died, said David Jones, a professor and historian of science at Harvard University. Some older adults in housing projects died at night because they feared burglars and were unwilling to open their windows or go outside to sit on their porches.

Environmental justice advocates trace this inequality back to decades of discriminatory housing policy, especially redlining — the 1930s government practice of rating neighborhoods’ investment worthiness using race as a determining factor and denying mortgages to minority buyers.

The labeling of minority neighborhoods as risky restricted resources for generations. It also starved those areas of parks and trees and affected how residents experience heat today. Comparing 1930s redlining maps with recent heat vulnerability maps by New York City’s health department reveals stunning correlations between how areas were categorized and where residents are most likely to die from heat.

“Those heat islands — they really are in those historically redlined neighborhoods, and that’s where the trees need to go,” Ulfelder said, referring to the urban heat island effect, where heavily paved areas with sparse vegetation trap more heat than outlying areas.

In the 1930s, the Home Owners’ Loan Corp. assigned Mott Haven a “D” grade, the lowest possible, for “hazardous.” For the adjacent neighborhood of Morrisania, the agency listed “Negro and Puerto Rican infiltration” and “obsolete homes” as “detrimental influences.”

Today, the South Bronx has some of the city’s lowest per-capita green space and is crisscrossed by power plants, waste stations and highways that cause severe noise and air pollution. Residents face high rates of infant mortality, cognitive issues, heart disease and asthma — so much so that Mott Haven is sometimes nicknamed “ asthma alley.” These conditions heighten heat vulnerability.

“Environmental racism in the South Bronx is in full view," said Arif Ullah, executive director of the environmental justice group South Bronx Unite.

Similar inequities have been identified across the country. In 2022, a Boston University analysis of 115 metropolitan areas from San Jose, California, to Louisville, Kentucky, and Hartford, Connecticut, found that air conditioning was less likely to be available in places with more residents who identify as either Black or African American or Hispanic or Latino.

In a bid to combat climbing temperatures, New York City Mayor Eric Adams activated the city’s heat emergency plan on June 18 for a week, designating hundreds of locations as air-conditioned facilities where residents can cool off during the day.