Some really pretty encouraging news coming from the Energy Information Agency (with a h/t to Climate Progress): The latest EIA figures show that coal use in electricity generation in the US has dropped to a new low, for the first quarter of 2012 just 36% of the energy mix. What's more, that's a drop of roughly 19% from the last quarter of 2011.
As for why, natural gas is displacing coal.
The EIA stats show natural gas making up 28.7% of the US electrical mix in the first quarter of the year—largely due to falling natural gas prices.
The good news in all this is that, for all natural gas's faults when it's obtained via fracking, conventionally extracted natural gas has much lower greenhouse gas emissions than coal (even when massive leaks and flaring is taken into account). It's far from perfect but its better than coal—though, really things would be far better if it was renewable energy sources displacing both coal and natural gas.
Fracking changes the equation though. The emissions of natural gas obtained via hydraulic fracturing have much higher total emissions than conventional extracted gas. The exact amount varies depending on who's doing the analysis, but on the high end it has emissions higher than coal.
Right now, natural gas from fracking isn't a huge part of the US natural gas supply, but the way things are going (the way the industry would like it to) it will make up an ever increasing supply, and in doing that the benefits in terms of emissions reductions of switching to coal from natural gas are diminished.