Someday, most large rooftops in urban areas in the United States will be green, not black. 

David Mellis points to an excellent article in Metropolis Magazine about Chicago's green roofs.  My European readers are probably already familiar with the green roof meme.

[David Writes]
So that's what the City Hall Rooftop Garden looks like. I pass City Hall on my way to work, but haven't ever been on the roof.

From a Metropolis magazine article about Mayor Daley’s Green Crusade.”

I intend to do everything I can to ensure that the City of Redmond leads the movement from black tar to green, bio-engineered roofs in the Puget Sound region. The benefits to the environment, living environment (summer temperature), and potential taxpayer savings in wastewater management are too promising to ignore.