I agree that over a span of thousands of years, or maybe even only hundreds, humanity could possiby take good advantage of some changes that might result from global warming, if they are not too severe. The more pronounced the changes, the longer it would likely take to adapt.

However in more personal terms, the damages of even moderate climate change could have enormous human and economic impacts. Even if large areas of northern Canada and Siberia were to become arable, vast areas of many lands would likely change form arable to arid, from being capable of supporting large populations to being capable of supporting lizards and cacti. I think that the negative changes would happen much faster than the positive ones.

If sea levels were to rise a few meters over, say, a couple of centuries, a lot of people would have to move and a lot of cities would have to be rebuilt in new locations. Proably not a lot of people would drown, but is two hundred years enough for such huge change to be absorbed with minimal human suffering and economic cost?

Ice ages may happen quickly in geological terms, but in human terms they would take "forever" to impact human habitations. Edmonton probably won't exist in it's present form, a thousand years from now, ice age or not, global warming or not, so ice age onset I believe is much less of an issue than rapid warming - in lifespan (or small multiples thereof) -like time periods.

But in any case, global warming is a plot by Canada and Russia to open up their vast northern lands, and international terrorism is simply a tool by which borders can be strengthened to keep starving, thirsty American south of 49, so shhh.