Axios: “Millions of Americans live in parts of cities where the “urban heat island” effect can significantly increase temperatures, especially during heat waves, per a new analysis by nonprofit climate research group Climate Central.

Why it matters: Heat islands — wherein heat is trapped by heat-absorbing surfaces and structures — can make cities less livable and increase the risk of heat-related health complications.

• They can also amplify the effects of already-dangerous heat waves, like the one gripping an expanding part of the U.S. this week.

What they found: 41 million Americans live in urban areas where heat islands raise local temperatures by 8 degrees or more, per Climate Central’s analysis of 44 U.S. cities.

• In nearly 10 cities — including New York, Houston and Los Angeles, for example — at least 1 million residents are affected by heat islands that raise temperatures by at least 8 degrees.
• Another way of looking at it: In five cities — New York, Detroit, Dallas, Houston and New Orleans — at least 70% of residents live in neighborhoods where the heat island effect can raise temperatures by at least 8 degrees.”