So... to start with, I'm not convinced yet about global warming, but I think your post is a bit disingenuous, lazs. The global warming folks have described the 'hard winters' as one of the symptoms of the climate change. Where you seem to be assuming that it's a straight 3-4 degree raise, they usually describe something more like a pendulum, where the summers are hotter, then the winters are colder, oscillating back and forth.
So... there are far better arguments to use in criticism of global warming, using one as weak as this just gives more ammo to that crowd (along the lines of "See, they don't even understand what we're arguing, how can you trust their suppositions if they don't even understand the material?"). Unless you're actually a global warming advocate, of course, and trying to use reverse psychology. But that'd just be silly.