How does eccentricity, tilt and precision affect the possibility of an ice age?
My theory was that the earth’s orbit around the sun has to be as elliptical as possible, and that the summer in north should happen when earth is farthest away form the sun and that the tilt should be as small as possible because then the north gets less sunlight a day. And that must be eccentricity (the orbit), precision (when the northern parts are “pointing” towards the sun, and tilt(how much light a day)? But I’m not even sure and I think it’s very hard to understand. Why would it be important of how much sunlight the northern parts get? Isn’t it as important how much sunlight the south gets?
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The reason is arctic ice.
Ice reflects most of the sunlight directly, in contrast to most other surfaces which absorb more of the sunlight and emit it later as infrared radiation. Since the greenhouse gases trap infrared radiation, but not visible sunlight, more ice means less greenhouse effects and therefore more cooling.
Therefore ice is a self-reinforcing feedback loop: At first, a small axial tilt means that less light reaches the polar regions, which means the polar regions get coolar, which means more polar ice, which means less absorbed light, which means it becomes even colder, and so on. In the past few million years, this cycle has often continued until major parts of Eurasia and North America were covered by a thick layer of ice.
That’s why the polar regions are important here. Regions that do not have any ice ever do not have an ice-related feedback loop.
Now for your question about the north being more important than the sourh: That’s because of the layout of the continents. The arctic is surrounded by lots of land, while the antarctic is surroundeed almost exclusively by sea. Since it is much harde for ice to form a solid sheet when the sea currents constantly deliver fresh water from warmer places, the feedback loop is much weaker in the south.
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