Because of natural gas.
This comes despite an administration that did everything it could to slow-roll the industry. From what little I know, this reduction in CO2 emissions was due strictly to the private sector and free market capitalism. I am not aware of any government initiative in the past two years that could account for the huge increase in natural gas. In fact, recent studies show fracking, which the EPA is trying to ban, is a significant reason for the decrease in CO2 emissions.
Oh, one more thing: the US is not a signatory to the Kyoto Protocol. Canada has formally withdrawn from the protocol.
Link here to CarpeDiem.com.
The link article is full of amazing statistics, most of which will not be re-printed in the New York Times.