Editor's Note: To learn more about using data for energy efficient buildings, be sure to check out VERGE@Greenbuild, November 12-13.

This week I spoke with Steven Avadek, Global Head of Sustainability, Reality Services, at Citigroup. We talked about his role at Citi where he is responsible for direct operational impacts such as energy, water, waste, green and LEED buildings. No small task given that Citi boasts 12,000 locations in 100 countries, possesses 75 million square feet of real estate, and whose annual energy consumption is equivalent to countries like Nicaragua and Senegal.

In many ways, Avadek’s job is made easier because of the imbedded corporate pro-sustainability culture within Citigroup. Indeed, its commitment to sustainability has not gone unnoticed. Citi has been recognized by IDG's Computerworld as one of the top green-information-technology organizations for 2010 and was the highest-rated U.S. bank in Newsweek magazine's Green Rankings. Citi also achieved the highest ranking among all companies globally in Newsweek's "Environmental Impact" category.

And this year Citi celebrated the milestone of certifying 200 LEED projects. By the end of the year, this number will be to the tune of 260. Progress.

I asked Avadek what makes a bank green — besides money of course — and he offered a three-part answer:

1. Operations. Real estate impacts and Citi’s impact on the environment.
2. Environmental and social risks. Ensuring that any Citi transactions are done in responsible and socially responsible way.
3. Financing. Using financing to promote environmentally sustainable business opportunities.

Avadek added that it is part of Citi’s DNA to have green language in their leases and to purchase green energy and noted that Citi is in the top 50 of green power purchasers in the United States. Citi also committed $50 billion to fight climate change.

Clearly if Citi does it right, there is a tremendous opportunity to have a significant impact and this prospect is what makes Avadek look forward to every day on the job. For a company whose real estate portfolio is equivalent to 33 Empire State Buildings stacked up one on top of the other, the sky is the limit.