In the past month, Phoenix experienced a string of four days above 115 F (46 C) for the first time and Boston hit 100 F for the first time in a decade. A deadly heat wave in the U.S. northwest, which scientists say would have been “virtually impossible” without human-induced climate change, baked Seattle at a record 108 F, while Portland, where roads buckled and power cables melted in the heat, reached an incredible new high of 116 F.
The intensifying heat is heightened in large urban areas by their design, according to a new report that has attempted to quantify where the “urban heat island” effect is most acute.
By applying an index based on land use, the amount of reflective surface, population density and other factors, researchers have determined that of 158 U.S. cities, New Orleans has the largest heat disparity with its immediate surrounds — an average 8.9 F hotter.
Newark, New Jersey has the second-largest heat island effect, an average 7.7 F hotter than its surroundings, while New York City is 7.6 F hotter. Houston is fourth on the list, followed by San Francisco.
Cities are usually hotter than nearby countryside because they generate heat through transportation, machinery and air conditioning that funnels hot air into the streets. A lack of trees, grass and other plants, which help cool the air, is compounded by the prevalence of miles of hard, dark pavement and buildings that soak up heat.