History tells us that climate change is responsible for the fall of most of the ancient civilizations--global change or local, it did't matter. In most cases, the end was hastened by the masses revolting against whatever institutions they'd erected--blaming them for the changing weather, thus destroying their civilization even before the changing climate drove them out of the area.
The climate has always changed and will always change--any talk of a 'normal' climate or 'lost tundra' is just plain stupidity. And mass stupidity is extremely dangerous.
Jonestown is a microcosm of what may happen if the environmentalists succeed in establishing the notion that humans are responsible for runaway climate change on a global scale.
A mere series of hot summers could lead to specific acts of self-destruction by otherwise sane countries like the U.S.A.--joining Kyoto comes to mind.