Climate, Methane and Carbon Dioxide Do We Have Them Back to Front?
By Keith Mellor
I wish to say from the outset that I’m not a climatologist but a retired engineer. However, science is based on evidence and argument, and that is what I’m presenting. The general consensus about carbon dioxide and methane is that they alter climate temperature, but I believe they have it back to front. This is important to recognise because decisions have been made which are both damaging to the economy and even the environment. I think the best evidence we have about climate temperature and the level of carbon dioxide and methane comes from ice core samples which date back to 800000 years ago, together with sedimentary rock covering that period. As you can see from the following image going back 420000 years, you would conclude that climate temperature is either controlled by the levels of these gases or visa versa. So, you have two possibilities.
This material is licensed under the Creative Commons Attribution-Noncommercial-Share Alike 4.0 International License Image showing 420000 years of atmospheric methane, carbon dioxide and climate temperature, taken from Wikipedia, Milankovitch cycles article
During that 800000 year period the main cause of long-term climate change is due to Milankovitch cycles, a concept developed by Milutin Milankovitch, a Serbian mathematician, astronomer, climatologist, geophysicist and civil engineer in the 1930s. Correlation with Milankovitch’s figures were made decades later with the study of deep sea sediment cores. These cycles are actually periods where the eccentricity of earth’s orbit changes, the inclination of earth’s axis varies, and earth’s precession continues to wobble. Earth’s inclination actually gives us our seasons, so when the earth’s axis increases the seasons become more extreme and the warm summers encourage deglaciation. Each cycle spans 41000 years.
The earth’s precession can be imagined like a slowly spinning out-of-balance top. This precession causes the summer and winter to be more extreme in one hemisphere than the other. Each cycle spans 26000 years. Earth’s orbit is almost circular and the variation in eccentricity over time is actually quite small. However, increased eccentricity does cause variation in climate temperature as you would expect due to being alternatively closer and then further away from the sun. Such a change from almost circular orbit will also cause a slight lengthening of some seasons and shortening of others. This cycle spans about 100000 years (although it varies between 84000 and 120000 years) and is thought to be the dominant one since about 800000 years ago. Prior to that, up to at least 3 million years ago the 41000 year cycle was dominant. Basically, these variations affect how the earth is warmed by the sun. Incoming solar radiation is referred to as insolation, and Milankovitch’s theory is referred to as orbital forcing. What he mainly focused on was the total summer radiation near to 65 degrees north, where ice sheets had previously formed.
So now if we look back at the above image showing climate temperature, together with levels of carbon dioxide and methane, we see that climate temperature reaches a maximum spike every 100000 years or so. This period is determined by the dominant Milankovitch eccentric cycle. As a result, climate has changed due to these effects, which have nothing to do with methane or carbon dioxide levels. From this, one can only conclude that climate temperature causes changes in carbon dioxide and methane levels, and not the other way around.
I know that only highlighting the 100000 year cycle does not give a full explanation of how these Milankovitch cycles fit in with real climate. This does not show the insolation aspect, but it’s enough to demonstrate the relationship with those gases.
Some may argue that the theory of Milankovitch cycles has to be modified and perhaps cannot explain as much as previously thought. Even if that is the case, when we look at the rise to peak temperature and fall every 100000 years, we know that this can’t just be the result of carbon dioxide and methane levels acting independently.
Others may argue that carbon dioxide causes global warming, even though the effect of orbital forcing was more dominant in the past. They may argue that the present higher levels have become more dominant and will therefore cause global warming. However, natural carbon dioxide levels around 3 million years ago were as high as total levels are now. Earth’s climate was warmer then with an ice cap only in Antarctica. However, the orbital forcing Milankovitch cycles was still the main factor controlling climate even though the dominant cycle was then 41000 years. There is no evidence that carbon dioxide or methane levels at that time had taken control of climate, but that they were simply reacting to higher temperatures. Therefore, when we look at today’s similar carbon dioxide levels there is no evidence that it is responsible for any global warming. The 3 million year plus example show that orbital forcing is still dominant.
More information can be found in the articles referenced below, although I don’t imply that any of the them agree with my point of view.
References:
NASA, Global Climate Change: https://climate.nasa.gov/news/2948/milankovitch-orbital-cycles-and-their-role-in-earths-climate/ American Museum of Natural History: https://www.amnh.org/learn-teach/curriculum collections/earth-inside-and-out/milutin-milankovitch-seeking-the-cause-of-the-ice-ages Climate Data Information: http://www.climatedata.info/forcing/milankovitch-cycles/ Patrick Tyson: http://www.climates.com/cc/ORBITAL%20FORCING.pdf Environment Counts.org: https://environmentcounts.org/ec-perspective-accounting-for-800000 years-of-climate change/#:~:text=Approximately%20800%2C000%20years%20ago%20something%20changed% 20in%20the extinguishing%20and%20changing%20nature%20and%20life%20on%20Earth. Sea Level Info: https://www.sealevel.info/co2 and ch4.html Wikipedia: https://en.wikipedia.org/wiki/Pliocene Wikipedia: https://en.m.wikipedia.org/wiki/Pliocene_climate