If implemented, they would represent a significant reduction in coal generation from about 39% of the mix to about 33%, a drop of about 15% from total 2012 coal generation (and under different scenarios it could be a bit more or less). The US economy has already seen a larger reduction in coal electricity generation — a 25% drop from 2005 to 2012 — and the economy appears to have survived intact.
However, despite this reduction, the overall change to the US electricity mix is best characterized as marginal, rather than revolutionary. This is especially the case from 2020 to 2030 where there is very little projected change in the mix.
In order to stabilize atmospheric concentrations of carbon dioxide at a low level (say 550 ppm or lower) requires that the carbon-free proportion of the global energy mix (not just electricity) increase from about 13% carbon free to more than 90%, regardless of how much energy the world ultimately consumes. The US in 2012 was about 13.5% carbon free. These regulations mainly switch electricity from coal to gas and thus do very little to increase the US proportion of carbon-free electricity generation.3