Summary: how orbital variations affect
sunshine
Obliquity
When obliquity is high, seasonality is enhanced. In mid and high latitudes, more sunshine comes in summer, and less comes in winter.
Averaged over the whole year, the high latitudes receive more sunshine, and the low latitudes
receive less.
Precession
When perihelion occurs at summer solstice, the contrast between summer and winter is enhanced. When perihelion occurs at winter solstice, seasonality is
weakened. Precession has little effect on annual mean sunshine.
Eccentricity
Changes in the eccentricity of the earthÕs orbit have very little effect on the annual mean sunshine
anywhere. However, they do have a large impact on the amplitude of the precessional cycle.
If the earthÕs orbit is very eccentric, the timing of perihelion in the calendar year becomes more
critical.