Milankovitch 100,000 years cycle problem

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Discussion Overview

The discussion centers on the Milankovitch cycles, specifically the 100,000-year cycle and its implications for Earth's climate and ice ages. Participants explore the relationship between Earth's orbital changes, eccentricity, and temperature variations, questioning how these factors contribute to the onset of ice ages.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Exploratory

Main Points Raised

  • Some participants express uncertainty about how much further from the Sun Earth would need to be for the 100,000-year cycles to account for ice ages, questioning if a distance of 10,000,000 km is necessary.
  • There is a discussion about whether a more elliptical orbit would lead to a net cooling effect, as one participant suggests that being further from the Sun during apogee and closer during perigee might cancel each other out.
  • Another participant argues that the effects do not cancel cleanly, noting that a more elliptical orbit could result in both colder and warmer conditions depending on the position in the orbit and the inverse square law of radiation absorption.
  • One participant provides a mathematical analysis of insolation changes with varying eccentricity, showing how average insolation increases with higher eccentricity, which could imply a warmer climate despite the elliptical orbit.
  • There is a challenge to the validity of the Milankovitch cycles in explaining climate changes, with some participants questioning how these cycles can be taken seriously if a more elliptical orbit is associated with increased warmth.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the implications of the Milankovitch cycles for climate change. There are competing views on whether a more elliptical orbit leads to cooling or warming, and the discussion remains unresolved regarding the adequacy of the cycles to explain ice ages.

Contextual Notes

Participants express various assumptions about the relationship between orbital eccentricity and climate, and there are unresolved mathematical steps in the analysis of insolation changes. The discussion also highlights the complexity of the factors influencing Earth's climate over geological timescales.

Bjarne
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According to the Milankovitch 100,000 years cycles, there is a problem.
The orbit of the Earth will change to a gradually more ecliptic orbit, and it will be a bit colder when this happen.
But the problem is that this is not enough to explain ice ages.
How much is missing.
I mean how much further away from the Sun should we get when the 100,00 years cycles should be the cause of ice ages. Is it for e.g; 10,000,000 million km further away from the sun?
http://en.wikipedia.org/wiki/Milankovitch_cycles
 
Astronomy news on Phys.org
I mean is it for example Is it for e.g; 10,000,000 km (not million km)
 
Do you mean that the orbit will be come more Eliptical? If so, if we become more elicptical, then we will be further from the sun during Apogee, but closer during Perigee than we are now, which should cancel out each other I thought.
 
Drakkith said:
Do you mean that the orbit will be come more Eliptical? If so, if we become more elicptical, then we will be further from the sun during Apogee, but closer during Perigee than we are now, which should cancel out each other I thought.

Yes this is what I mean
I am not sure this will cancel out each other, not according to Milankovitc so far I understand
 
Bjarne said:
Yes this is what I mean
I am not sure this will cancel out each other, not according to Milankovitc so far I understand

Hrmm. I don't think I can help you on this one, sorry.
 
Things don't cancel cleanly.

On one hand, you might think that more a more elliptical orbit means a colder Earth. Objects move slower at aphelion, so Earth will spend more time farther than average than closer than average.

On the other hand, you might think that a more elliptical orbit means a warmer Earth. Perihelion is subject to the inverse square law, so a little closer means a lot warmer.

Inverse square wins. More elliptical means more insolation/year (warmer).
 
Tony, you are saying that because of the inverse square law the amount of radiation absorbed by the Earth when it is near the sun will more than cancel out the lesser amount when the Earth is further away?
 
The amount of radiation absorbed is proportional to the inverse square of the distance. Let's look at an orbit with a semi-major axis of 1 AU. If circular, let's call the amount of insolation 1. Now let's consider an orbit with an eccentricity of 0.1. This means that perihelion is at 0.9 AU and aphelion is at 1.1 AU. The average amount of insolation received while at these extremes is
((1/0.9^2) + (1/1.1^2)) / 2 = 1.03
Partially offsetting this is the fact that a planet will spend more time at aphelion.

Here's a table showing how much additional insolation a planet receives due to eccentricity. Insolation = 1 for a circular orbit.
Code: 
0.0    1.000
0.1    1.005
0.2    1.021
0.3    1.049
0.4    1.091
0.5    1.155
0.6    1.251
0.7    1.401
0.8    1.668
0.9    2.300
 
Ah ok i see. Thanks Tony.
 
  • #10
tony873004 said:
The amount of radiation absorbed is proportional to the inverse square of the distance. Let's look at an orbit with a semi-major axis of 1 AU. If circular, let's call the amount of insolation 1. Now let's consider an orbit with an eccentricity of 0.1. This means that perihelion is at 0.9 AU and aphelion is at 1.1 AU. The average amount of insolation received while at these extremes is
((1/0.9^2) + (1/1.1^2)) / 2 = 1.03
Partially offsetting this is the fact that a planet will spend more time at aphelion.

Here's a table showing how much additional insolation a planet receives due to eccentricity. Insolation = 1 for a circular orbit.
Code: 
0.0    1.000
0.1    1.005
0.2    1.021
0.3    1.049
0.4    1.091
0.5    1.155
0.6    1.251
0.7    1.401
0.8    1.668
0.9    2.300

How can the Milankovitch 100,000 years cycles then be taken serious?
It should according to that (which I understand many supports) be colder when the orbit is more elliptical..
 
  • #11
Bjarne said:
How can the Milankovitch 100,000 years cycles then be taken serious?
It should according to that (which I understand many supports) be colder when the orbit is more elliptical..

All else being equal, the planet should get warmer when the orbit is more elliptical, as it intercepts more solar radiation per orbit.
 

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