Science/Astronomy:

* Why We Must Flee the Planet: The Geometry of Earth is All Wrong

http://www.space.com/searchforlife/060629_seti_thursday.html

A sphere has less surface area than any other form of the same volume.

To quote:

Consider the Tonnage-to-Terran ratio, an index of how efficiently we use the planet: With the human population at six billion, the T-to-T ratio works out to about a trillion. In other words, for every lout strutting Earth's stage, there are about a trillion tons of Earth!

That's right: each of us is backed up by a trillion tons of natural infrastructure, a mostly useless collection of crushed iron core and creamy, hot magma, topped by a delicate continental crust. This, as you can easily surmise, is wasteful. It's possible to live the good life with 100 tons of housing (including some office space and a car or two), which is 10 billion times more efficient.

So while moving some of our descendants to Mars or the moons of Jupiter, as Hawking suggests, will help—it won't help much. The problem is that these worlds are also spheres. The amount of increased real estate they offer for human settlement is unimpressive.