See excerpt from go green blog..
Federal agencies never realized the scale of its carbon emissions without the mandatory emissions reporting in the past. The US government is known to be the largest polluter in the entire country and energy reform would compel it to conduct a comprehensive emissions reporting.
While the House of Representatives may have passed their own climate related Act during early 2009, it is not clear whether the Senate will act anytime soon regarding their own version. This has caused environmental advocates around the world to sharply criticize the US for recalcitrance. Obama’s executive order goes some way to appease the critics, as agency emissions account for a very considerable part of the country’s overall footprint.