Actually, a lot of people dont really get this, but we ARE currently in an ice age.
In geologic terms, any time that the planet has ice anywhere on the surface year round, it is in what is called "Ice House" conditions. The amount
of ice that is locked up at any one time may vary, but if there is ANY, it is technically already an ice age.
At any time that ice does not exist year round on the surface, it is what is called "Hot House" conditions. Also, contrary to popular opinion, the
entire surface of the planet will NOT flood like in the movie Water World (God what a hokey movie). There simply is not enough water on the planet to
do so.
Granted, a lot of land surface will be inundated (most of Florida will be gone, as well as most current coastal areas). Given complete 100% Hot House
conditions, with NO ice cap whatsoever, there would likely be an approximate sea level rise of around 10 meters. Coast lines would move inland
significantly, and there is a good chance that new inland seas will be formed... But there will still be sufficient land to survive on.
Conversely, in the event of Ice House conditions (at least worse than what we are experiencing now), the entire surface of the planet would not be
covered in ice. Granted, a good deal of water would be locked up in ice at the poles, and the glaciers would indeed move south as they did about
40,000 years ago. Sea level would drop, a new land bridge between Alaska and Siberia would open along the Beiring Straights. Significant new real
estate in the continental shelf would be exposed, and would spring up as incredibly fertile coastal plains. The tropical regions would shrink and the
temperate climates would move closer to the equator.
Although your high lattitude residences would now be akin to living in Dead Horse Alaska, there would still be mroe than enough livable space on the
planet (indeed in Ice House, there would be MORE space) to support the Human Race.
Also, PLEASE dont panic thinking this is going to happen overnight.... Ice Ages come and go on a regular basis, and have been doing so for MILLIONS of
years. (It has been extremely well documented) Its nothing new. We just havent been around to see them as a species (at least not in a way that we
could record it in technicolor). On average it will take over 1000 years (probably more) for such a drastic climactic change to occur.

