The 110-story Sears Tower in Chicago will soon get a $350 million retrofit aimed at reducing electricity use in the tower by 80% over five years.  The 4.5 million sq.ft. building will employ upgrades in the glass exterior, internal lighting, heating, cooling and its own green power generation utilizing wind turbines on its rooftops. 

According to an article in the NYT, "buildings are among the world’s largest contributors of greenhouse gas emissions. After the retrofit, energy savings at the Sears Tower, which is to be renamed the Willis Tower this summer, would be equal to 150,000 barrels of oil a year, officials said".