According to a recent estimate, CO2 emissions in the RGGI region experienced a significant decrease from 2005 to 2009 -- approximately 33%. What's been overlooked is the key role natural gas played in that drop. Here's the relevant chart:

No doubt there are several important factors driving the emissions drop -- the recession, the weather, increased energy efficiency, and increased renewables capacity, among them. But what's worth underscoring is the 31.2% coming from fuel switching. That's all from natural gas -- specifically, generally decreasing natural gas prices that were lower than petroleum prices after 2006 and much closer to coal prices by 2009. Per another excellent chart:

This trend could be very important for our climate future. It suggests natural gas might actually be the viable transition fuel that's been heavily promised. Though of course much more research and analysis needs to be done on that front before a firm conclusion can be drawn. Nevertheless, natural gas prices are now something very much worth watching in the coming years.