Milankovitch 100,000 years cycle problem

[Bjarne]

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

 

[Bjarne]

I mean is it for example Is it for e.g; 10,000,000 km (not million km)

 

[Drakkith]

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.

 

[Bjarne]

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

 

[Drakkith]

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.

 

[tony873004]

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).

 

[Drakkith]

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?

 

[tony873004]

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.

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

 

[Drakkith]

Ah ok i see. Thanks Tony.

 

[Bjarne]

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.

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..

 

[tony873004]

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.