Re: What would be the result of a horizontal spin for a planet's axis?

Thank you Anthony, great question! First it might interest you to know that while most planets in our solar system have rotational axes very roughly perpendicular to the orbital plane, Uranus does not. Uranus orbits the sun with a rotational tilt of 97.77 degrees. And this does indeed have extreme impact on its climate. This means the poles receive direct sunlight. However climate interaction is quite complex. For reasons still not well understood, the equator region of the planet is still warmer than the poles.

So what would happen if an earth-like planet suffered a similar fate? It would be a dramatically different planet. At first glance seasons would be very harsh, with one pole receiving direct light while one is in total darkness. But the specific impacts are difficult to predict. One pole is water while there is a land mass on the other. Currents would still distribute the heat, albeit differently. Depending on when the tilt originates, the basic development of the earth could be different. Sun-facing polar regions would be unable to sustain ice caps, while winter at the other pole would likely be very cold. Equatorial regions would have to rely on ocean currents to sustain temperature. But the dynamics could change the currents. In the end, like Uranus, while quite different from the earth we know, it is difficult to predict exactly what it would be like.

One final note - it is not necessary for such a dramatic shift in tilt of the axis to affect climate. Our axis exhibits "axial precession". This occurs on about a 26000-year period. Right now perihelion occurs during the southern hemisphere's summer and aphelion during the southern hemisphere's winter. When all things are otherwise equal, the southern hemisphere's summer is warmer and winter is colder... for now. This will gradually change until the situation is reversed in about 13000 years.

Here are some related links for additional reading:
http://en.wikipedia.org/wiki/Milankovitch_cycles
http://www.crh.noaa.gov/fsd/?n=uranus