US emissions of carbon dioxide blamed for climate change fell in 2011 and have slipped to a 20-year low this year as the the world's largest economy uses more natural gas and less coal, data shows.
The surprise drop from the world's second biggest emitter comes despite the lack of legislation on climate change but it was unclear if the change marked a trend or would be enough to meet goals on fighting global warming.
Official data showed that energy-related US carbon emissions fell by 2.4 percent in 2011 from the previous year.
The decline did not fully track the broader economy as the United States posted growth in 2011, whereas the last time emissions declined was in 2009 during a contraction in the economy.
In the first three months of 2012, US carbon emissions from energy use were down by almost eight percent from the same period last year, marking the lowest level for the quarter since 1992, the Energy Information Administration said.