E=0. What Does That Mean for the Seasons?

[JohnWDailey]

Currently, Earth's eccentricity (orbital shape) is 0.0167086. Zero is a perfect circle whereas One is parabolic escape orbit and any greater becomes a hyperbola. And in the theory of the Milankovitch cycles, Earth's eccentricity varies between 0.000055 and 0.0679 over a period of 100,000 years. This affects the seasonality of planet Earth, as an extreme ellipsis can result in longer seasons.

Let us assume that Earth's eccentricity today does not exist, leaving it instead in a perfectly circular orbit. What would a circular Earth orbit mean for the seasons and the climate?

 

[mfb]

An eccentricity of 0.0167 means the distance between Earth and Sun varies by 3.3% between perihelion and aphelion. Sunlight intensity varies by 6.6%.

Currently we have perihelion when it is winter in the northern hemisphere, and aphelion when it is summer there. This reduces the differences between the seasons a bit. In the southern hemisphere we have the opposite, increasing the differences between the seasons a bit. With 0 eccentricity, that effect would vanish.

5% eccentricity leads to 10% distance difference which leads to 20% difference in sunlight intensity. That is quite a notable effect.

 

[DrGreg]

On the other hand, spring and summer together last three days longer than autumn and winter, in the northern hemisphere (measured equinox-to-equinox, in a non-leap year).