Looking at a map of annual temperatures across the U.S., it’s clear that the entire country is getting hotter. But when you zoom in on a new app that shows county-level heat data, disparities emerge. That app is based on research that looked at surface temperatures within more than 1,000 U.S. counties and found that for a majority, areas with higher rates of poverty can be nearly 7 degrees hotter in the summer than the richest communities nearby.
Income difference isn’t the only factor associated with higher temperatures; that research, from the University of California San Diego’s School of Global Policy and Strategy, found that even when controlling for income, non-white neighborhoods were hotter than the predominantly non-Hispanic white areas.
To get these findings, which were recently published in the journal Earth’s Future, researchers used satellite data that measured land surface temperatures for 1,056 U.S. counties that have 10 or more Census districts, and compared those measurements to Census-district demographic information. Temperature can vary so much across an area, says Susanne Benz, lead author of the paper who was a postdoctoral fellow at UCSD at the time of the study, that it wasn’t enough to look at temperature measurements from individual weather stations, which can be spread out over wide geographic areas. Satellite data allowed Benz and her postdoctoral supervisor Jennifer Burney to look at temperatures across all developed land in the continental U.S.
In 76% of those counties, the poorest neighborhoods were hotter in the summer than the wealthiest. Within a single county, the difference between rich and poor communities could be up to about 6.5 degrees. That extreme gap was seen in 10% of the counties with the biggest difference—the greater the divide between rich and poor in a county, the greater the heat disparity, Benz says—while the average of all the counties was a difference of about 2.5 degrees. In 71% of the counties, this disparity held true along racial lines even when controlling for income, though the maximum temperature difference was slightly lower at around 4.9 degrees between the most and least non-Hispanic white neighborhoods. The average of all counties along racial lines was about a 1.8-degree difference in surface temperatures.
The researchers measured surface temperatures, which do differ from ambient air temperatures, but the threat of extreme heat is still clear; more than 700 people die annually from extreme heat in the U.S. “Hotter areas are more expensive, so you need to pay more for cooling your house,” Benz adds, noting that the burden is even greater on poor, minority communities to deal with this heat. “This is one of the areas where being poor costs more money than not being poor.”
There’s a few reasons why poor, minority communities are hotter than affluent, white ones. Poor neighborhoods and neighborhoods of color tend to have less tree canopy coverage, more asphalt streets, and greater building density, all of which adds and retains heat. This is the urban heat island effect, a phenomenon cities across the country are attempting to mitigate. Richer, white areas tend to have parks, tree-lined streets, and fewer swaths of asphalt. Population density contributes to higher temperatures too, though Benz says it’s not as great of an impact as you might expect. Still, more people in one area means more body heat, electricity use, and so on, which can bump up the temperatures.
That heat disparities exist along income or racial lines is not a completely new revelation—previous research has linked redlining to higher temperatures and looked at just how many fewer trees exist in low-income neighborhoods—but this latest research reinforces the depth of the issue, showing that it exists everywhere, not only in major cities plagued by the urban heat island effect. “For the longest time the discussion has always been … this is a New York problem, a Los Angeles problem. We really showed it’s not,” Benz says. “It’s in the Midwest, it’s in your hometown.” She hopes the app, which is powered by Google Earth Engine, helps people see that this problem is at their front step, and not only within major cities that may be far away.
These findings also clearly show, says Benz, that this is a systemic issue. The counties the research looked at have different histories, are different sizes, and were not all redlined, and yet a majority showed this temperature disparity along wealth and racial lines. That means there isn’t one easy solution, either—previous research has found that adding trees to poorer neighborhoods can increase housing prices, potentially forcing poor residents out of the area once heat mitigation measures are put in place. “We need to look at this holistically, including the housing crisis,” Benz says. “We need to change the way we do urban planning.”