# Are there “eccentric seasons”, where do they occur, and why don't we hear more about them?

The earth is on an eccentric orbit. It's a small eccentricity (let's say e=0.01 https://www.wikiwand.com/en/Orbital_eccentricity) but it's there.

As it moves closer and farther from the sun the amount of energy being absorbed from the sun's light will change, and thus there will be a temperature shift dependant on earth's eccentricity (an "eccentric season")

The flux on earth and thus the rate it which it absorbs the sun's energy goes as r^-2, where r is the orbital radius. Thus the fractional change in flux is proportional to 4e. (taking into account the factor of 2 from the orbit ranging from a(1-e) to a(1+e) where a is the semi-major axis)

The effective temperature (assuming a blackbody) goes as (P)^0.25, where P is the incident power (= flux on earth * cross sectional area of earth).

Thus, for small e the fractional change in temperature should be ~ e.

For Earth, with a temperature of roughly 300 K, this gives a 3 degree temperature shift over an orbit.

I'm not sure I've ever heard anyone talk about this, and it doesn't seem negligible (especially given that there are parts of the world where seasonal temperature changes only by about 10 degrees http://ggweather.com/sf/narrative.html).

So my three questions are:

a) Is the above logic correct, are there (small) "eccentric seasons"

b) Where would they occur, specifically what latitude if any has a boosted seasonal change?

c) Is this something talked about that has just passed me by (wouldn't be the first time)?

• you should give a link. The seasons we have , summer autumn winter spring are dependent on the orbit, so I cannot understand what you are asking about. – anna v Feb 9 '18 at 14:28
• sorry if that was unclear, I've renamed them "eccentric seasons" to better distinguish them – Zephyr Feb 9 '18 at 14:38
• Maybe this will help , I will read it later aa.usno.navy.mil/faq/docs/seasons_orbit.php – anna v Feb 9 '18 at 14:43
• Are you aware that in the northern emisphere winter occurs when the earth is closer to the sun? The relevant effect is the angle of incidence of light. This is a coincidence: the perihelion shifts over time. So are you asking if the perihelion shift will have an effect on seasons? – John Donne Feb 9 '18 at 15:00
• Yes, this is dealt with. The climate model I work with for instance has parameters for orbital eccentricity and uses this to calculate the effective solar constant which, as you say, varies over an orbit. I think it does not deal with Milankovitch cycles (ie, the parameters which vary over those cycles are treated as constants). The same model is used for weather forecasting so the eccentricity is also taken into into account for that. I don't have specific answers as to how great the effects are (hence this is a comment, not an answer). – tfb Feb 9 '18 at 16:32

• @tfb - That is correct. Apparently slightly elevated $CO_2$ levels helped the Earth dodge a glaciation bullet half a millennia or so ago, when conditions were close to but not quite ideal for the onset of a glaciation from a Milankovitch cycle perspective. Amplifying factors such as albedo also play a very important role. And so does climate. Whether snow falls predominantly on Siberia vs North America is one of the proposed solutions to the 100000 year problem. – David Hammen Feb 9 '18 at 17:17