The first problem I can think of offhand is that sudden radical changes to environmental temperatures and weather patterns affect plants and pollenators, all of which are adapted to their current weather, temperature, and soil conditions. We're not talking about the sudden sterilization of the surface of the earth, or anything, but we're talking about a significant die-off of all but the most hardy and adaptable species over a geologically rapid span, and then another one later when the systems that depended on those other species are interrupted by scarcity of food or environments that allow proliferation and breeding.

Loss of biodiversity is no joke, and it seems to be one that is lost in the shuffle while people talk about how human beings can adapt to the changes. Bees cannot hedge their bets. Birds cannot wear sunglasses. Frogs cannot wear sunscreen. This seems like kind of a minor deal until you consider that the relationship between pollenators and plants is why we can breathe, and why our crops proliferate and feed us.

You also can't dump billions of tons of shattered ice caps into the ocean without affecting global weather systems. I'm not terribly thrilled with the idea of MORE severe weather developing in formerly temperate, calm areas, I dunno about you.