All U.S. cities experience some level of “heat island effect,” in which heat reflects off hard surfaces, intensifying the impact of the hottest days. But as climate change intensifies, nine U.S. cities are special islands unto themselves, according to an analysis released Wednesday that coincides with a heat wave enveloping much of the nation.
The nine — New York, Houston, Los Angeles, Dallas, Chicago, San Antonio, San Diego, Phoenix and Detroit — each have more than 1 million residents enduring temperature increases of 8 degrees or more, because of the heat island effect. That’s according to Climate Central, a nonprofit science and news organization, which has sought to create a broad snapshot of the largest urban populations at risk.
“Anyone who steps out on a sunny sidewalk can feel the difference from when they are in their yard,” Jen Brady, Climate Central senior data analyst, said in an interview. “Obviously, in the city there’s fewer trees, fewer yards and more sunny sidewalks. Those places are going to be warmer. What we’ve tried to do with this analysis is quantify it.”
Forty-one million residents among all nine cities experience the temperature boost, some up to 10 degrees or more, exposing them to higher risks of heat-related illness and more expensive cooling costs, the study found. Climate Central’s analysis did not include demographic data, Brady said, but other organizations such as the D.C. Policy Center have conducted research showing that lower-income communities face disproportionate impact from the heat island effect, partly because their neighborhoods often lack trees.
Brady and her team used census tract-level data from 44 U.S. cities to answer a question they often hear.
“A lot of people have said to us, ‘Is it really getting hotter or is it the urban island effect?’” Brady told The Washington Post. “We really wanted to clarify that the heat island effect is additional heat in the environment, but that climate change is increasing the baseline heat in the world.”
The Climate Central analysis comes as scientists say the world is experiencing its hottest month on record, with 17 days in July recording record-breaking heat, based on 40 years of global observations.
The future also looks ominous. The average number of Americans experiencing at least three consecutive days of temperatures 100 degrees or higher each year will climb from 46 percent today to 63 percent over the next 30 years, according to a Post analysis of data provided by the nonprofit First Street Foundation.
Numerous factors can influence the degree the heat island effect further raises temperatures. Cities with taller buildings, more density and fewer trees face hotter conditions than other U.S. cities, studies have shown.
The data for cities such as New York, Houston and Los Angeles can be grim, but that does not mean cities are powerless to decrease the heat island effect, Brady said.
Communities can plant trees and keep an eye on neighborhoods with higher heat island effects to ensure that people are not getting sick and have access to cooling centers, Brady said. Urban planners can paint highways and assist homeowners and landlords with roofs in lighter colors to reduce the heat.