[Snowless (OP)]

Hey everyone. I know this might not immediately seem like a question for this section, but it's actually based in Astronomy.

I'm currently reading Origins by Lewis Dartnell. According to the book, there are lakes in East Africa where humanity evolved that were called Amplifier Lakes and every 800K years would undergo quick cycles of filling and draining that helped to drive human evolution. During maximum eccentricity (when the Earth's orbit is most elongated), changes in the precession cycle (the wobble of the earth's axis), would cause the lakes to undergo the cycles. But, the eccentricity cycle is 100K years and the precession cycle is 26K years. So, I'm wondering why this phenomenon only occurred every 800K years. Why didn't it occur every 100K years?

I'm guessing it's the result of some complicated interplay between the precession cycle needing to be at a certain point during maximum eccentricity, but I would appreciate any elucidation on this. Thank you.

[evan_au]

The Milankovitch cycles originate in the gravitational interplay of the Earth, Moon and planets, orbiting the Sun.
- As astronomical effects, they are chaotic, but fairly predictable (at least on the millions of years timescale)

However, the behavior of Earth's atmosphere is highly chaotic - beyond the daily and annual cycles, it is currently not really predictable beyond 2 weeks*.
- And the response of climate is also highly non-linear, with hysteresis effects like: If the Earth's poles are cold, they will reflect Sunlight back into space, and stay cold; but if the Earth's poles warm up, they will absorb Sunlight on land/sea, and stay warm.
- And quite random events like supervolcano eruptions or rerouting of ocean currents can cause major climate shifts, at least within a hemisphere.

So, while the Milankovitch cycles are a fairly predictable input into climate models, they are not the only factor.
- Rather than driving the climate equilibrium directly, they may provide enough of a push to move the climate into a new equilibrium (or not)
See: https://en.wikipedia.org/wiki/Milankovitch_cycles

*We are now also starting to get an understanding of the El-Nino Southern Oscillation, which gives some general weather guidance out to 3-6 months.

[Petrochemicals]

The Milankovitch cycles originate in the gravitational interplay of the Earth, Moon and planets, orbiting the Sun.
- As astronomical effects, they are chaotic, but fairly predictable (at least on the millions of years timescale)

However, the behavior of Earth's atmosphere is highly chaotic - beyond the daily and annual cycles, it is currently not really predictable beyond 2 weeks*.
- And the response of climate is also highly non-linear, with hysteresis effects like: If the Earth's poles are cold, they will reflect Sunlight back into space, and stay cold; but if the Earth's poles warm up, they will absorb Sunlight on land/sea, and stay warm.
- And quite random events like supervolcano eruptions or rerouting of ocean currents can cause major climate shifts, at least within a hemisphere.

So, while the Milankovitch cycles are a fairly predictable input into climate models, they are not the only factor.
- Rather than driving the climate equilibrium directly, they may provide enough of a push to move the climate into a new equilibrium (or not)
See: https://en.wikipedia.org/wiki/Milankovitch_cycles

*We are now also starting to get an understanding of the El-Nino Southern Oscillation, which gives some general weather guidance out to 3-6 months.

Having a brief skit of that I see 400,000 years mentioned for eccentricity, if the tilt misses one then catches the next, hey presto 800,000.