That's because they think all of the fresh water from the glacial melt will trigger a shutdown in the Atlantic halocline which makes most of the eastern seaboard temperate and keeps jolly ol' England warm and moist as well. Not only will it vastly change local temperatures (including the tropical ones where the cool water no longer returns) it will change salinity and pH, all of which are not conducive to fish stocks and coral reef and such.

So, it might be that the current trend of global warming is indeed a buildup toward the hard freeze. But like you said, everyone has a theory. I daresay it's hard for anyone to ignore the evidence now. But I find it fascinating that our pollution might be our salvation if it keeps things artificially warm enough to prevent an ice age from starting. (note: that doesn't mean I think we SHOULD continue to pollute)