Temperature versus CO2 – the big picture

11/28/2018 16:11 - Posted by Tom van Leeuwen
When discussing “Climate Change” it’s good to have an understanding of how the Earth’s climate has changed in the past. That will give us a reference to decide whether the current changes are normal or not.

Global temperatures have varied a lot over the last 500 million years. Depending on the timescale used, the current temperature is either cold or hot, so when you want to know the “normal temperature” you’ll have to indicate what timescale you’re using.

The role of CO2 has been heavily disputed over the last century. In 1970, scientists were convinced CO2’s greenhouse effect was already saturated, even at concentrations measured at the beginning of the Industrial Revolution (1850) when CO2 was at around 300 parts per million. Saturation means that adding more CO2 has no measurable effect on global temperatures.
Later some climate scientists started to doubt that fact, so it’s important to include CO2 concentration measurements or proxies in this overview.

The geological timescale – 570 million years

On this timescale, we observe the largest climate fluctuations. Continents were formed and ocean currents changed in the process.
Temperatures were very high, 15 to 20 °C higher than now. During most parts of this period, no sub-zero temperatures were measured anywhere on Earth, so ice-caps were absent.
CO2 levels were very high, above 5,000 parts per million during most of this period. That’s 12 times the current levels. Live on Earth flourished, the continents were covered with thick woods and in the oceans, coral riffs started to grow. Carbon deposits were created in the form of deep ocean sediments, carbonaceous rocks and fossil fuels like coal, oil and natural gas.

55 Million years ago, with CO2 levels still well above 1,000 ppm, global temperatures started to decline sharply. These CO2 levels are considered extremely dangerous by the IPCC and according to them, those concentrations could cause a runaway warming process. Real-world measurements, however, show us the contrary. Temperatures declined.
This contradicts the CO2 greenhouse gas hypothesis.

It’s very clear that seen on this timescale, both the modern temperatures and CO2 concentrations are extremely low. There is, however, no clear correlation between temperature and CO2 levels. Other factors like continent formation, volcanism and ocean currents ruled the climate changes.

The Quaternary timescale – 2.5 million years

This timescale is marked by the latest and current ice age.

Over 30 glacial periods have been defined in this period. These glacial periods are separated by interglacials, each one of them lasting around 10 thousand years. The Holocene is the current interglacial we’re living in.
In one complete glaciation cycle, worldwide average temperatures fluctuate around 12 °C between the deepest glacial minimum and the warmest interglacial optimum.
Over this whole period of 2.5 million years, both the Earth’s polar regions present permanent land ice. As a result of glaciations, the North Pole ice cap can reach as far south as the current locations of New York and London.
In the figure above, we observe the latest three glacial cycles.
Seen on this timescale, we currently live in a warm period that has enabled humans to develop. However, we observe that the current interglacial is not as warm as the previous ones. Current temperatures are not extreme in a Quaternary context.

During the Quaternary, CO2 concentration and temperature have tracked closely. That raises the question about causation and effect.
If we follow the “official” greenhouse gas hypothesis, as published in the various IPCC reports, temperature follows CO2 concentration. So, the relation would be:

Unknown cyclical forcing (???)

CO2 concentration fluctuations

temperature fluctuations

That leaves a big question: What caused the CO2 concentration to behave this way? What cyclical forcing caused carbon to be released from its natural deposits like deep-sea sediments, carbonaceous rocks, fossil fuel deposits and CO2 dissolved in seawater?
Do we have evidence for... something like cyclical volcano eruptions, repeating every 100 thousand years? Mysterious cyclical vertical ocean currents that transport carbon-rich sediments to the surface every 100 thousand years? Or Intelligent life appearing every 100 thousand years, burning fossil fuels and then disappear?
No. There seems to be no logical answer to this question.

If we take the CO2-temperature relation the other way around, we obtain the following line of reasoning:

Milankovitch cycles

temperature fluctuations

CO2 concentration fluctuations

Now everything fits together.
The Milankovitch cycles are small alterations in Earth’s orbit around the Sun, like the orientation of Earth’s axis (precession), eccentricity and variations in the axial tilt that create cyclical variations in the solar energy input. These external influences result in the cyclical temperature fluctuations known as glacials and interglacials, more or less the same way the Earth’s axial tilt creates the seasons but with a much longer cycle length.
Warm oceans can contain less CO2. So, when oceans warm, CO2 from the oceans is released into the atmosphere.
As CO2 levels are extremely low at the onset of each warming cycle, well below the saturation point of its greenhouse effect, there might be a small positive feedback of CO2-induced warming that helps the other natural factors to lift the Earth out of each glaciation. But when temperature CO2-concentration reaches a certain level the warming stops.

We must conclude that CO2 concentration trails temperature. Temperature fluctuations are the cause, CO2 level variations are the consequence.

To give the figure some perspective, the modern CO2 concentration spike is included at the far right side of the graph. It is quite clear that CO2 levels have exploded over the last 100 years, completely out of sync with natural variation. Most likely this increase is due to human emissions. The carbon that was stored in the form of fossil fuels is released, using its chemical energy for human development: food production, transportation, medicine, and other human welfare enhancements.
Although the CO2 levels have risen by almost 50%, there is no corresponding spike in worldwide temperatures. More about the Modern Warming Period later in this article.

The Holocene timescale – 10 thousand years

Fifteen thousand years ago, global temperatures started to rise as Earth came out of the latest glacial period.

Welcome to the Holocene!

This interglacial has allowed the human race to develop like never before.
The Holocene Optimum was reached 8 thousand years ago with temperatures around 4 °C higher than today. Since then, temperatures have steadily declined, with some ups and downs like the Minoan Warm Period (3,500 years ago) the Roman Warm Period (2,000 years ago), the Medieval Warm Period (1,000 years ago) and the Little Ice Age that ended 200 years ago.
On this scale, we’re living in a cold period recovering from the extremes of Little Ice Age. Over 90% of the Holocene has been warmer than today.

CO2 levels have been rising over the last 8 thousand years to around 300 parts per million at the end of the Little Ice Age.
So, temperatures fell while CO2 concentration increased. This contradicts any claim that there is a positive correlation between CO2 levels and global temperature.

Modern Warming – 200 years

Temperatures are recovering from the coldest period of the Holocene, the Little Ice Age, so there has been some warming over the past 200 years.
There have been intervals with a clear correlation between CO2 and temperature, but during two periods, from 1940 until 1975 and since 2000 until now, the correlation has been inversed. Rising CO2 concentrations coupled with falling temperatures.
This is in contradiction with the CO2-hypothesis.


  • Global temperatures are recovering from the coldest period (Little Ice Age) of a warm period (Holocene) within one of the coldest periods (Quaternary) of Earth’s history
  • It is not true that we are breaking temperature records. Moreover, we’re much closer to breaking all-time cold records then all-time highs
  • It is true that CO2 concentration levels are the highest of the past 2.5 million years
  • It is true that rising CO2 levels are due to human carbon emissions
  • It is not true that these high CO2 levels are a threat to life on Earth. Life started and thrived at much higher global temperatures and CO2 levels
  • It is not true that CO2 concentration fluctuations are the main driver for temperature variation. None of the four timescales we've observed show evidence of a clear positive correlation between CO2 and global temperature.
So the CO2-hypothesis is contradicted by real-world, empirical observations.

View the facts without prejudice.

Tom van Leeuwen, November 2018.


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The fingerprints of the greenhouse effect

The hypothesis of "man-made climate change" tells us that the increase in the concentration of CO2 enhances the greenhouse effect of the atmosphere and has global warming as a final result.

Since the beginning of the industrialized era around 1850, man emits relatively large amounts of CO2 into the atmosphere through the use of fossil fuels. The consequence of these emissions is that during that period, the concentration of CO2 in the atmosphere increased sharply from about 300 parts per million to more than 400 ppm, an increase of almost 40%. The average temperature increased in the same period more or less 1.5 °C with a small variation depending on the data source used.

Why did the warming stop?

The political reports of the IPCC are based on the hypothesis that CO2 is the most important control knob of the Earth's temperature. The problem is that this hypothesis does not correspond at all with the empirical data available to science. Forecasts are made using models that are not capable of 'predicting' the past.

CO2 Band-Saturation Explained

Professor at the Geophysical Sciences department at the University of Chicago David Archer describes the band-saturation of the CO2 greenhouse effect. After that, everything goes wrong.

The first part of the lecture is very informative. Professor Archer explains in great detail how the CO2 greenhouse absorption works, it's logarithmic nature and the band saturation. He even shows on a working instance of the MODTRAN model how adding the first ppm of CO2 to the atmosphere has a huge impact on the atmosphere's energy balance. Adding more CO2, the effect fades away.

Hydroelectricity and greenhouse gasses

Hydropower is one of the cleanest energy sources available. The only downsides known so far are the impact on the landscape and the risk of a dam breaking due to earthquakes. Carefully choosing the locations and high construction standards are needed to solve these problems.

Besides electricity generation, dams also help to regulate the water flow in the rivers, making them better navigatable and useful for irrigation.

So, overall it seems to be quite positive, but recent research has "discovered" a new downside to hydroelectricity and it's a usual suspect: Greenhouse gasses.

The world needs more CO2

Interview with Professor William Happer of Princeton University. Mr. Happer is a renowned physicist, specialized in the field of atomic physics, adaptive optics and spectrometry. This interview from 2015 is part of the series "Conversations that Matter."

Some quotes from this interview:

The logarithmic nature of the CO2 greenhouse effect

For many people, a logarithmic relationship can be a fairly abstract concept. It is hard to imagine the implication that it has on the strength of the greenhouse effect that corresponds to the amount of CO2 that humanity emits into the atmosphere. Here we present a visualization to explain in a simple way what we are talking about.

CO2 is a greenhouse gas. The presence of CO2 in the atmosphere traps a part of the infrared radiation that the Earth's surface emits into space. The total greenhouse effect of the Earth's atmosphere is about 30 °C, without this effect, the temperature would be -15 °C instead of +15 °C, the actual current average temperature.
Water vapor is the most important greenhouse gas. CO2 provides 3 °C of heating, that is, 10% of the total effect.

When the concentration of CO2 increases, its greenhouse effect also increases, but not in a linear fashion, but logarithmically. For each increase in concentration, the effect on temperature is less and less.

Water vapor

Water vapor is the single most important greenhouse gas. It makes up 80% to 90% of the total greenhouse effect of the Earth's atmosphere.

Climate models depend on water vapor as a positive feedback for supposed CO2 warming. In these models, CO2 causes a tiny warming that causes the relative atmospheric humidity to increase. That increase in water vapor produces the catastrophic warming they predict.
The problem is that in the real world, while atmospheric CO2-concentrations increased by almost 30% since the end of World War II, the relative atmospheric humidity has been stable at low altitudes and has even decreased at higher altitudes.