No they won't. At least not substantially. And not alone.
Let's think about this a little. Where do electric cars get their electricity? From a power plant, most of which are fired by some sort of fossil fuel (and until nuclear becomes much bigger than it is, that ain't gonna change, as I have chronicled elsewhere in these pages). The Laws of Thermodynamics indicate that adding another part to the cycle increases inefficiencies. consequently, using electricity from a 35% efficient power plant through power lines with huge losses to a battery that is inherently inefficient doesn't reduce (alleged) GHG emissions.
Hybrids are ok, I suppose. I helped build one in college (I designed part of the drivetrain). But a diesel-powered VW Jetta gets 50 mpg. I don't think there are any hybrids currently getting that kind of mileage. And the Jetta performance is superior at a lower price. Why would I pay the premium for a hybrid?
In the end, AGW will be shown to be a hoax and the only reason to buy electric or hybrid will be economic. Right now, it isn't.