"Unequal distribution of radiation due to earth axis tilt is the ultimate driver of the weather."

You first have to distinguish between incoming solar radiation (visible wavelengths) and outgoing longwave (infrared wavelengths) radiation due to the earth's finite (above absolute zero) temperature.

Secondly, even if the earth's axis tilt would be zero, unequal distribution of incoming solar radiation would still occur, due to the fact that the earth is *ROUND*! This occurs because radiation striking the ground near the pole spreads radiation over a larger area than when it strikes over the equator. Moreover, energy travels a larger distance through the atmosphere at higher latitudes. Those *two* factors combine and cause the incoming solar radiation to be quite variable from equator to poles.

Thirdly, outgoing infrared radiation does not vary as much from latitude to latitude, because from an absolute temperature point of view, the earth's temperature does not vary that much. If one would then plot a graph showing the latitudinal variation of both the incoming solar and outgoing infrared radiation, one would see that the *net* (incoming - outgoing) radiation is negative at high latitudes (poles) and positive at low latitudes (equator). This means that the equatorial regions are continuously heating up while the poles are cooling down.

If the atmosphere wouldn't exist, like on the moon, the earth's surface would reach a radiative equilibrium that would lead to much higher meridional temperature variations than what we see in reality. But because of the atmosphere, this radiative forcing quickly leads to complex atmospheric motions that try to mix the warm equatorial air with the cold polar air. Finally, the tilt of the earth's rotation axis simply modulates this radiative imbalance throughout the course of the year. By no means is it a driving force of the weather and climate!

I know you can't include this in your web page, (NOTE: I just did) but if you want to replace the above-quoted phrase, I would suggest something like:

Unequal distribution of radiation due to the sphericity of the earth is the ultimate driver of the weather (and climate).

Richard Harvey

Canadian Centre for Climate Modelling and Analysis

Victoria, B.C.