Arizona’s largest city is an “urban heat island,” a phenomenon that pushes up temperatures in areas covered in heat-retaining asphalt and concrete. Phoenix on Wednesday recorded a sweltering 116 degrees (46 Celsius), setting a new high for the date. Phoenix officials say they are tackling urban warming, monitoring downtown temperatures, planting thousands of trees and capturing rainwater to cool off public spaces. …But climate specialists like Brian Stone, who runs the Georgia Institute of Technology’s Urban Climate Lab, said more is needed.  In urban heat islands, solar radiation and hot air from vehicles and buildings get trapped between high-rises. There aren’t enough trees to provide shade and evaporative cooling that can bring down temperatures. “We are working against a pronounced warming trend in large cities, and so it will require a substantial resurfacing of urban environments simply to slow the rate of warming,” Stone said.