New York City's iconic Empire State Building - once the tallest skyscraper in the world - is now going to become one of the greenest buildings in the world. 

The historic landmark is getting a makeover, which building owners say will reduce energy use by 38 percent after the project is completed in 2013. The initial renovations come at a cost of $20 million and are expected to help save $4.4 million a year in energy costs. 

Built in the 1930s during the Great Depression, the 102-story Empire State Building is a giant art deco structure made of concrete. Inside are offices, restaurants and plenty of tourists, who come for the breathtaking views of the Manhattan skyline.

Empire State's prominence is what prompted owners to embark on a massive four-year project to reduce its carbon footprint and energy consumption.

The landmark will undergo a series of renovations, including replacing all of the skyscraper's 6,500 windows with insulated glass that will reduce heat in the summer and trap it in the winter. 

"What we are going to do is keep all the positive benefits of the windows and reduce some of the negative benefits," says Paul Rode, a project executive. "There will be triple-glazed windows with an insulation value almost as great the walls that they are connected to."

Extra insulation will also be installed behind radiators to save heat.

Other plans include installing energy-efficient lighting, upgrading the building-control systems to make them more energy efficient and adding modern air-conditioning and heating systems whose output adjusts with usage.

"One of the things we will be doing down here is taking these machines and making them more efficient.  And we're doing that by stripping everything off this unit that you see," Rode explains. "We're then going to put new tubes in and rebuild everything with high-efficiency equipment. In this manner, we'll be able to reduce the energy consumption of this machine and all the machines down here by almost half."

This would in turn help reduce carbon dioxide emissions from the building by some 105,000 tons a year.

Building owners says retrofitting old buildings to be more environmentally friendly is key to reducing levels of heat-trapping greenhouse gases in New York, nearly 80 percent of which come from city buildings.

"One of the key essential goals that we're trying to get across to folks across the world is that doing this is good business," Rode says. "There's no reason why this could not be done anywhere, and a decent return made anywhere in the world."

But Rode says upgrading infrastructure is not the only way to reduce energy consumption. People need to modify their habits, too.