Why do we need Revised Milankovitch cycles?

The Milankovitch cycles have been taken into account in some climate studies, but so far without a clear definitive conclusion if these cycles are driving the climate or not.

In this chapter I will show updated graphs that can be used as input in the discussions about the exact role of the Milankovitch cycles on Earth’s climate. I call those graphs the ”Revised Milankovitch cycles” because of 2 reasons:

• Milankovitch did not study planetary precession . It was discovered more recently and measured to have a period of about ~70k years against ecliptic and ~112k years against ICRF. I call this type of precession Inclination precession. The current value – according to Wikipedia  - in 2,000 AD is ~1.57869°. We need to take this movement into account as well. In my view this is actually the MAIN driver for the climate on Earth as researched by e.g. Muller and McDonald (1997). For more details see this paper  and this paper  and this paper  and this paper  about Orbital inclination, not eccentricity being the driver for the 100-kyr glacial cycle.

• The eccentricity, obliquity and inclination precession numbers are different according to the model described in this book compared to the original Milankovitch study. We need to use the right input numbers to get the proper output.

Additionally what is good to know upfront: The Interactive 3D Solar System Simulation only shows the bigger movements. So the fact we are coming from a small ice-age is not (yet) added in the simulation.

Climate debate

But maybe to start off, I would first like to give my reflection on the current state of the climate change debate. First of all, the words “never” and “records” in climate debates really only means “since 1880 AD”, the commonly recognized year from which we have trustworthy weather measurements records. That is not that long compared to the precession cycles we are talking about in this book. There are off course paleoclimate models dated back longer ago, but they will never tell the full story like we have since 1880 AD.

Additionally, since we are coming from a small ice age, taking the year 1880 AD as starting point will automatically result in wrongly “global warming” conclusions. The timelines are way too short to be able to make such statements.

Also taking the increase of CO2 PPM as a baseline of the “global warming” discussions seems to be incorrect. As can be quite clearly concluded, the amount of CO2 follows the temperature cycles, and there is (so far) no conclusive evidence it is driving it. The warmer it gets, the more CO2 is released from the sea .

The level of CO2 in the air is not that high compared to earlier era’s:

The current CO2 level of 425 PPM is still extremely low on the geologic time scale. Plants grow best with CO2 at between 1,200 and 1,600 PPM because that was the level they evolved in for hundreds of millions of years. During the last glacial maximum the CO2 level fell to only 170 PPM. That’s the lowest it had been since life first colonized land over 500 million years ago. We should all be grateful it didn’t fall any further because at anything less than 150 PPM all plant life dies, and that would’ve caused the greatest mass extinction since the “Great Dying,” at the end of the Permian period, around 252 million years ago, when 96% of marine species and 70% of terrestrial vertebrate species went extinct. Some scientists attribute the extinction of the megafauna that took place in various places around the world from between about 10,000 and 50,000 years ago to dangerously low CO2 levels.

Additionally as we add more CO2 to the atmosphere, the effect of extra CO2 as greenhouse gas decreases. This article  and this article  coming from the skeptical science website explains in more detail why this fact “Lambert Beer” law is still bad news for the climate. The main reasons are however not due to the level CO2 in the atmosphere.

Ever since ~10,000 BC we are in a relative warm period and as historic records show, in one moment in time will move to a new ice age. The only way to prevent this, is if we use climate changing techniques to make sure it is getting warmer. The current climate change agenda that wants to prevents it getting warmer might therefore just be counterproductive in keeping the climate the same .

But I also have to be humble. I do not know what the correct approach needs to be and I am sure no one really knows what is going on, how the trend will continue in the future and what is the best response we should give. Therefore, lets at least agree to be careful.

Let’s move along on this topic.

Current version Milankovitch cycles

This picture coming from this paper  shows all the currently known inputs for the Milankovitch cycles. You can find it on the internet on a lot of sites.

Revised Milankovitch cycles

I have modified the picture to give an overview of all the movements as presented in this book.

As can be seen all current theories about precession, eccentricity, obliquity, inclination, etc. ARE NOT CONNECTED to each other at all.

My conclusion would be precession, eccentricity, obliquity, inclination, etc. are CONNECTED to each other

That is the difference.

More background information

This picture comes from this paper  and shows the temperature and CO2 variations on Antarctica. I have added the Inclination precession cycle (in blue) and the obliquity precession cycle (in amber) in the picture to show the pattern.

• The inclination pattern (blue) / combined with the obliquity (amber) climbing seem to match as the explanation for the end of ice ages and particular the end of the last glacial maximum (LGM)  around max inclination in 20,496 BC.
• The Obliquity pattern (amber) seem to match as the explanation for the Younger Dryas period  around max obliquity in 9,800 BC.

Paleoclimatic studies show cycles of 100k, 23k and 19k year cycles.

If you do a search on google for the length of the axial precession you will get many hits with all sort of numbers. The foundation of the numbers should actually be found in paleoclimatic studies.

There are many papers that clearly mention 23k and 19k year cycles. For instancethis paper in nature  or this paper . The 19k, 23k, 100k year cycles are part of this model.

I am not a climate expert, but hopefully with the information as provided in the Excel, this book and the Interactive 3D Solar System Simulation - which can be considered as an add-ons to the currently known Milankovitch cycles - scientist can gain better understanding of the effect of all precession movement on the climate cycles as experienced on Earth.