Milankovich Cycle revisited

Michael Davies
Junceira Cao Sertainho
21 OCTOBER 2010

OF THE EUROPEAN UNION AS THE SOLE AUTHOR OF THIS WORK. I acknowledge the owners of the freely available scientific literature and various websites on which I conducted my research.


In my previous essays I considered that the Earth acted as a thermal amplifier. In this essay I will expand and consider the roll of each of the two feedback components. In doing so I will attempt to explain the reasons for some of the problems with Milankovich theory. This new theory ignores minor forcings and feedbacks such as sunspot activity and thermohaline circulation which act over smaller periods and are irregular as well as normal variations of the climate system. It is essentially a theory of energy and heat over millenia and carbon cycles which have a period of >100Myrs


1. Insolation (total INcoming SOLar radiATION) is the variation in solar radiation received by the earth due to its orbital dynamics and the total solar radiation available. This is described in the theory of Milankovich cycles. 

2. The earth has a developed atmosphere which contains trace amounts of greenhouse gases, i.e. C02, CH4 and water vapour.

3. Feedback, for the purpose of this theory only two feedback mechanisms will be considered, i.e. C02 and ice.

4. The Thermal Amplifier Model is as per my previous essay.

5. The effect of increased glaciation on temperature can be seen in the 5 Myr graph below.

Fig 1. Five Million Years of Climate Change


There are several problems with solar forcing which are highlighted in the Wikipedia article on Milankovich cycles.

These are the 100kyr problem, the 400kyr problem and the transition problem, the article uses the above graph to highlight some of these issues.

The answer to these problems can be found in the above graph, where it can be seen that continental ice formation has increased the negative temperature by a factor of up to 5 over the recording period. The essay will consider the roll of C02 and Ice as forcing or damping agents.

To do this I have divided the graph into 3 sections. 

  1. From 5 Myr to 3.3 Myr the temperature variation is +/- 1degC at Vostok equivalent temps >0degC, this is modeled in my thermal amplifier theory, as C02 >Ice. That is the feedback from C02 is greater than the feedback from ice, and the temperature is both more stable and varies with the principle Milankovich cycle variation.
  2. From 3.3 Myr to 1 Myr temperature variation increases to +/- 2degC at Vostok equivalent temps -1 to -3 deg C, this is modeled as C02 >~<Ice. That is the feedback from Ice becomes increasingly more dominant and amplifies the temperature difference between peaks.
  3. From 1 Myr to 14 kyr temperature variation increases to +/- 5degC at Vostok equivalent temps ave -3 to -4.5 deg C, this is modeled as C02<Ice. That is feedback from ice becomes the dominant mechanism. Because the ice feedback has more than one component it overpowers the C02 damping signal. The components are a decrease in insolation due to increased albedo and increased C02 absorption in the Hydrosphere. The transition from 41kyr to 100kyr cycles occurs because Ice has become the dominant feedback mechanism, large peaks in Insolation can overcome the Ice feedback, but small peaks cannot. During cycles of low amplitude the persistence of Ice overcomes radiative forcing, this is the answer to both the transition problem and the 100 kyr problem. The dynamics of the feedback mechanisms may also explain the 400 kyr problem.

                      fig 2 420 kyr of ice core date from Vostok

The Vostok 400 kyr graph with temp, C02, Benthic 02, CH4 and radiative forcing shows 10degC variations in temp and similar variations in CH4 C02, for normal variations in radiative forcing from 420 kyr bp to 14 kyr bp.

The Graph does not show glacial ice coverage, but there are indications on the graph that initial temperature decreases are semi independent of C02, probably due to Increased Albedo. Eventually the C02 levels fall and rapid temperature decrease are seen. For the subsequent insolation cycles the temperature variations are +/- 2 deg C until the next Interglacial or Interstadial.


The model considers that the Earths long term Climate is a function of Insolation and 2 feedback mechanisms. The variation in global temperature is a function of Insolation. The level of average temperature is a function of atmospheric C02. The variation in Glacial cycles is a function of Ice. Increasing C02 amplifies average temperature but dampens the variation in temperature. Increasing Ice attenuates temperature and amplifies temperature variation.

Insolation is a function of orbital dynamics and the sun, and as such is not currently controllable. Ice is a function of average temperature and is both uncontrollable and inimical to life. C02 is a function of the Earth and has a long term techtonic variation with a period of over 50 Myr. But it is also a function of the short term carbon cycle and is available to humans for fine tuning the global temperature.

C02 is the dominant component of Global temperature at atmospheric levels >250ppm. Current C02 levels of 400ppm should shield the earth from future glacial advances.

C02 is good ICE is the killer, learn to manage C02 and control the EARTH’S CLIMATE for the good of the BIOSPHERE.

Mike Davies
October 2010


About madmikedavies

Retired Communications Engineer, living in Portugal. Interests are Cosmology, Earth Sciences, Organic farming, Climatology, Football, Golf, Birdwatching, and Dogs
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