Then we had better go back into an ice age then, fast. Sounds like things were so much better when everything north of the 49th Parallel was frozen under a mile thick sheet of ice. I would say there is a hell of a lot of advantages to the planet warming to its more "normal" temperature, and not having permanent ice sheets. Not the least of which is a hell of a lot more of the small portion of the planet that is not permanently underwater becomes habitable by a hell of a lot more of the ecosystem. And not "one trick ponies" that require a very specific ecosystem that almost nothing else can live in.