Bill Clinton and NYC Mayor Michael Bloomberg are joining forces to cut energy use at the Empire State Building by 38 percent, saving $4.4 million a year in energy costs.

The $20 million makeover will include replacing 6,500 windows, reduce its carbon dioxide emissions by 105,000 metric tons during the next 15 years, and give tenants web-based systems for managing their energy usage. Former President Clinton and Mayor Bloomberg both attended the announcement on the Empire State Building’s 80th floor on Monday. The hope is that this renovation will set the bar for other older buildings and landmarks. Experts say retrofitting old buildings to be more environmentally friendly is an important step in reducing greenhouse gases.

“This New York icon is sending really a strong signal to the rest of the world that going green, even in the current economic crisis, is an economic and environmental imperative,” Clinton said.