Orbital Forcing - The Changing Arctic Environment: The Arctic Messenger - page 380

1. Orbital eccentricity:
The shape of Earth's orbit varies over a cycle of 100,000 years - from being nearly circular
to mildly elliptical. At present, we are near the minimum of the cycle (almost circular), with
only about a 6% difference in the amount of solar energy reaching Earth between perihelion
(smallest Earth-sun distance) and aphelion (largest distance). However, when Earth's orbit is
at its most elliptical, this solar energy difference is between 20 and 30%, which significantly
increases or reduces the amount of energy received by Earth during different seasons, even
though the net energy gain will be more or less constant.