A question for the astronomers in the audience...

[andrewducker]

How much longer would the Earth's orbit around the sun have to be for (most of) the planet to be uninhabitable?

Would 10% do it? The poles get pretty damn chilly as it is, if we added another month in there between December and January, would the whole of Europe be similar?

Comments

[cheekbones3]

There are a wide range of hypotheses, there's a rough consensus of 5% closer being lethal, further out though, there's apparently much more potential for variance - atmospheric insulation will be very important.

http://en.wikipedia.org/wiki/Habitable_zone#Solar_System_estimates