The sphericity of the Earth causes the angle at which sunlight hits the ground to vary with latitude, which leads to a variation of insolation with latitude. The problem is, that the outgoing IR radiation is nearly uniformly distributed with latitude. This means that there will actually be no radiative equilibrium at any latitude, except 37N and 37S. So, the tropics should be getting hotter over time and the polar regions colder over time.

Sensible and latent heat transfer comes to the rescue again. Weather systems and storms serve to transport excess energy from the tropics toward the poles. The general atmospheric circulation also does this. In addition, a considerable amount of heat is carried poleward by ocean currents.