It has played backdrop to King Kong movies, a few Frank Sinatra cameos and a plane crash. Now New York's most iconic building is getting the biggest eco retrofit in U.S. skyscraper history.

The crusading green team at the Clinton Climate Initiative will spearhead a $500 million project to green the Empire State Building. The retrofit will seek to minimize energy usage in all of the building's systems, especially  its electrical delivery which incorporates 2,500,000 feet of electrical wiring to carry 40 million kilowatt hours a year to tenants.

The retrofit will be finished by the end of 2010, a bit longer than the frenetic 145 days required to construct the 103-floor building in 1930 and 1931. It was an odd time to debut the building at the start of the Great Depression, but the new overhaul to promote cost-savings and energy efficiency dovetails appropriately with the new hard times.