Earth: Half ice, half desert

[ejordan]

Could anyone speculate as to what sort of environmental/astronomical climate shifts or conditions it would take to cause Earth's northern hemisphere to be completely covered in ice & snow, and Earth's southern hemisphere to engulfed in a perpetual heat, covered with sand dunes?

I am doing some research and would like to hear peoples opinions as to what would cause a climate condition such as this on Planet Earth.

Thanks,
Eric

[HardScienceFan]

Not possible,heat flow doesn't work that way.

[Harpo]

It would take an extreme tilt of the planet, so that the southern hemisphere be in permanent daytime (and eternal summer) while the northern hemisphere be in permanent nighttime (and eternal winter)

Can't happen.

[Triceratops]

Not with earth's present rotation/axis cycle. You will always have two polar regions. Geometry is the simple teacher here.

Tri

[chrispenycate]

Now, that's interesting; I'd answered this one. Never mind.
To get that, it's not going to require a cilmate shift, but stopping the Earth's rotation (tidal locked, same face always towards its primary, kike Earth's moon- actually "stopping" isn't precise - you're synchronising the day with the year.) Venus and Mercury are almost tidally locked, Next, to get your "Northern hemisphere /southern hemisphere" split, you're going to have to rotate the planet through the other dimension (North/south rather than East/ west) and stopped again. It would be much easier to get Eurasia facing the sun, while the Americas froze.
While the synchronisation of the orbit and rotation could happen naturally in a few billion years (well, actually the sun would probably expand and vaporise the planet before it got properly synchronised) or you could spiral the moon out, pulling rotary momentum with it, or make a huge lobe in the Earth's magnetic field which would, over a few millenia, interact with the sun's magnetic field to slow the Earth's rotation.
But if you had a colony on a planet orbiting a red dwarf star within the liquid water (inhabitable) zone, in all probability the natural state of that planet would tidally locked.
May I ask why you require these conditions, and what percentage survival on the planet's surface you require? I might be able to do it with a single comet strike, but the destruction would be impressive (consider as one of the problems the effect on the oceans of stopping the rotation. Tidal wave? It would be higher than mountain tops - weee! I doubt that 1% of humanity would survive, and species extinction would be in the same order.

G Wells "The man who could work miracles" only a bit more catastrophic, anyone?

[PTeppic]

If you can get hold of a high school geography text book it should have sections on climate and land conditions. It's a few years since I studied it(!) but:
a) there'd probably need to be an axis tilt/rotation for starters
b) the permanent ice is probably easier to achieve, since it "simply" requires a sufficient cooling to re-build the "Ice Age" but with the new axis keeping all the ice to one hemisphere
c) the problem with sand dunes is that they're not simply a product of heat and low precipitation but often over-grazing etc. The existing tropics, which already receive overhead sun most of the year, are not desert but quite the opposite, with thick, lush forest and humid, heavy plant growth.
d) the effects of land-mass, sea temperatures and the wind patterns will also affect the above.