"Substituting gas for coal does reduce emissions, but there is...

"Substituting gas for coal does reduce emissions, but there is still far too much carbon in natural gas to allow its widespread use if the electric system is to reduce its emissions by 80 percent by 2050. That was the national goal endorsed by President Obama when he ran for president in 2008.

In fact, some electricity experts say that if the economy as a whole has to cut emissions by 80 percent, the electric sector will have shoulder even deeper reductions, given that other areas, like transportation, can probably manage less."

-- Source
http://green.blogs.nytimes.com/2012/02/10/natural-gas-vs-nuclear-power/