If there is a 500-pound gorilla in the room with green buildings, it is the millions of square feet in existing property that needs to be retrofitted in order not to release environmentally harmful carbon emissions into the atmosphere. Today, CB Richard Ellis, the world’s largest commercial real estate services firm, announced that it has set a goal to become carbon neutral by 2010. The larger impact, however, will be the firm’s commitment to work with the owners and tenants of the 1.7 billion sq. ft. CBRE manages to reduce carbon emissions and save energy.

“To be able to move those principles and ideas [from new green construction] into existing buildings is going to really have the impact that we need to in terms of reducing CO2 emissions from our built environment,” said Ashok Gupta, air and energy program director for the Natural Resources Defense Council, in a press conference today.

Founded in 1970, NRDC is a national nonprofit organization of scientists, lawyers and environmental specialists dedicated to protecting public health and the environment. The environmental group is working closely with CBRE to pinpoint best practices to save energy and reduce carbon emissions in the firm’s buildings and in the properties that they manage. Commercial buildings are responsible for 40% of carbon emissions, which have been associated with global warming trends, according to NRDC.

“CB Richard Ellis has an unsurpassed ability to influence how real estate is built, sourced, occupied and sold. With leadership comes the responsibility and we feel it is critical to be on the front of environmental sustainability,” said Brett White, president and CEO of CBRE.

“CBRE, in the field of property management, is really a new and important player in the global warming policy debate,” said Gupta. “So far you’ve seen power companies, car companies and others engage in global warming issues.”

So how much of the massive managed portfolio is already moving towards energy efficiency? “I think it is a fair assumption to say that most owners and occupiers globally are cognizant and aware of the issue of environmental sustainability,” explained White. “I think it’s also fair to say that most owners and occupiers are already engaged in a dialogue of how they can reduce their environmental footprint through the space that they occupy or own.”

In the U.S., CBRE is implementing the Environmental Protection Agency’s EnergyStar programs in more than 125 million sq. ft. of space. That accounts for every U.S. office building managed by the firm that measures more than 100,000 sq. ft. “We expect that at least 100 buildings will achieve an EnergyStar 75 rating — which means they are the top 25% in their peer group — by the end of this year.”

White also noted that clients such as TIAA-CREF, for whom CBRE manages almost 14 million sq. ft. and Behringer Harvard, for whom the firm manages almost 12 million sq. ft., are mandating EnergyStar benchmarking. “We set a goal of reducing energy consumption at the office buildings we represent by 10% during 2008,” said White. “At an average current cost of about $2.50 per sq. ft., a 10% reduction will save property owners and tenants more than $30 million on an office portfolio of under 125 million sq. ft.”

CBRE will replicate its U.S. effort in Asia and Europe as the next steps in the global initiative. Properties will be reviewed to see what can be accomplished through smarter operations and to identify which mechanical or technological changes are necessary to reduce individual carbon footprints.

The business opportunity, according to White, isn’t necessarily additional revenue but will differentiate the firm for clients looking to hire property managers with environmental expertise.