In part because of heavy growth – particularly in the Phoenix metro area – heat is being reflected, trapped, and absorbed in concrete, rooftops, and a maze of buildings that blocks wind. At the same time, there's little vegetation to absorb the heat, and high energy usage generates more.
It's called the "urban heat-island effect," and whatever the impact of global warming here, this phenomenon is sending the mercury rising. On Tuesday, Phoenix tied the all-time record of 28 days at 110 degrees or greater in one summer, reached in 1979 and again in 2002. If the temperature rises to 110 degrees one more day this year, Phoenix will set a record.