PowerPoint Presentation - No Slide Title

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 earth’s 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 earth’s orbit is very eccentric, the timing of perihelion in the calendar year becomes more critical.