Scientists from around the world are meeting in Berkeley to consider ways to cool them down.
The Claremont Hotel has what scientists call a cool roof.
"You get the additional gravy of air conditioning energy with air quality benefits and more importantly global cooling effects," said Hashem Akbari, PhD from Concordia University.
Scientists from around the world are studying urban island heat and its effects on global climate changes. Cities can be 20 degrees warmer than rural areas because the buildings, streets and sidewalks retain heat.
Scientists say the solution starts at the top.
"In places that are hot, you'll pay a price for that. Your roof will be hot, the heat will leak into your building. The answer is to turn up the air conditioning and that's an expensive alternative," said Melvin Pomerantz, PhD from Lawrence Berkeley National Lab.
Time for change that won't break the bank, they say. The Bay Area Air Quality Management District has launched a clean air plan.
"To encourage cool roofing, cool paving, planting shade trees. A comprehensive strategy to keep temperatures manageable," said David Burch from Bay Area Air Quality District.
You know how when it gets hot a doctor tells you to wear light, reflective clothing, the scientists have the same prescription. Imagine office buildings and homes in cool colors. It would improve air quality and bring temperatures down.
They hope to launch a cool cities plan in 100 cities worldwide.
"This is not the silver bullet to the problem of global warming. But it is a measure that we can do right now," said Akbari, PhD.