Under former Mayor Richard Daley, Chicago launched several green building initiatives in the early 2000s. In 2002, the city constructed the Chicago Center for Green Technology, the first rehabilitated municipal building to receive an LEED Platinum rating, and a resource for those curious about green building [source: Chicago Center for Green Technology]. Soon after, Chicago began requiring LEED certification for all city buildings, and any building projects receiving financial or zoning assistance from the city had to incorporate green features. Its Green Permit Program also awards projects that incorporate certain sustainable features with a faster permitting process and reduced permitting costs [source: City of Chicago].
As of 2012, the U.S. Green Building Council counts 794 registered or certified LEED projects in Chicago, the third most in the nation [source: USGBC]. The city possesses more than 4 million square feet (371,612 square meters) of green rooftops, which absorb rainwater and help regulate building temperatures [source: Richardson]. The Willis Tower -- the tallest building in the Western Hemisphere (formerly known as the Sears Tower) -- began undergoing a retrofitting in 2009 to cut its energy consumption by 80 percent, derive power from solar panels and wind turbines, and incorporate other sustainable features [source: Stern].