Why CO2 levels change after temperatures change.

Cause and Effect. No issue is more turned upside down in the global warming debate than global temperatures and CO2 levels. That CO2 levels change during the past glacial and interglacial periods is very well documented. It has been used as the basis for climate sensitivity calculations by many warmists. There is one problem with determining the climate sensitivity based on CO2 feedback forcing. It assumes that at least some of the temperature change is caused by changing CO2 levels.

The Inconvenient Skeptic

Typical example of a chart that is used to "prove" that CO2 changes cause global temperature changes

What if the reverse is true?  What if CO2 levels have primarily been determined by the ocean temperature and there is no significant forcing from additional CO2 in the atmosphere?  Here is what is known. In the transition from the last glacial to the Holocene interglacial, the polar temperatures increased about 12 °C, while CO2 levels increased from 185 to 265 ppm, or about 80 ppm for the comparable time frame.

It is widely accepted that CO2 is released into the atmosphere when the oceans warm, but lets take a look at exactly how much is released. This is greatly simplified because the solubility is linear from 0C to about 18C. Since this is also the primary range that is affected during the transition from glacial to interglacial I am going to use linear behavior.

The Inconvenient Skeptic

This shows that warm water holds less CO2 than cold water

Since the Earth’s atmosphere weighs 5E18 kg, the mass of CO2 at the two levels are:

(185 ppm/ 1,000,000) * 5E18 kg = 9.25E14 kg

(265 ppm/ 1,000,000) * 5E18 kg = 1.33E15 kg

So the beginning of the Holocene saw ~ 4E14 kg of CO2 emitted into the atmosphere by the oceans. All very naturally. Someone had better figure out how to get the EPA to stop the oceans from polluting like that.

Now the assumptions start to enter in. Basically I am going to assume that most of the CO2 that gets released is held in the colder polar waters. This is  supported by (Martin, Basak, 2010). So an assumption that 25% of the Earth’s oceans warm by 12 °C will be the starting point. I will also limit this to the top 1 meter of water for the starting point.

One quarter of the Earth’s oceans have a surface area of 9E13 m2. Since I am only doing a rough estimate right now I will use a fixed density for the oceans at 1023.7 kg/m3. That brings the total mass of one quarter of the oceans for a depth of 1 m to be:

9E13 m3 * 1023.7 kg/m3 = 9.24E16 kg

Now it is simply a matter of plotting the CO2 that is released for each 1 °C change in water temperature.

The Inconvenient Skeptic

CO2 Released by 1m of warming polar oceans.

The result is almost dead on. Simply adjusting the impacted depth from 1 m to 3.5 m describes the total amount of CO2 that was added into the atmosphere as the result of the actual temperature change. The amount of CO2 released is in fact much greater than this due to the plant growth that takes place to fill the land that thaws out by the retreating ice sheets.

If the CO2 levels are dependent on temperature, then how is it possible to determine the climate sensitivity based on CO2 forcing? It is perfectly clear that CO2 levels in the atmosphere changed directly as a result of the warming, but there is no evidence at all that the CO2 caused any of the warming.  Here are the NH summer energy, temperature and CO2 are plotted together chronologically.

The Inconvenient Skeptic

NH Summer Energy, Temperature and CO2 Levels for the past 25,000 years.

The warming that led to the Holocene is initiated by the increase in NH solar energy which started to increased 22,000 years ago.  Several thousand years later the warming was starting in Antarctica.  The warming oceans around Antarctica started releasing the absorbed CO2 into the atmosphere.  Once the NH solar energy stopped increasing, so did the warming.  Once the warming stopped, CO2 stopped increasing.  The order of events is very clear.  Changes in solar energy cause warming.  Warming oceans release CO2 into the atmosphere.

In situations where there is a temperature change that involves large bodies of water below 18 °C, CO2 levels will increase with warming water and drop with cooling water. In no way does it show that temperatures changed as a result of increased levels of CO2.  The correlation of CO2 levels in the atmosphere to global temperatures shows only that a change in water temperature will cause CO2 levels to change.  There is no reverse evidence that changing CO2 levels in the atmosphere cause a change in temperature.

The atmospheric concentration of CO2 would appear EXACTLY the same as it does for the Holocene warming period regardless of any positive “feedback” from CO2.  Based strictly on the sequence of events, the correct statement is that CO2 levels in the atmosphere are dependent on the changes to the temperature of the polar oceans.  There is no dependence of global temperature on changes in CO2 levels.

It should also be noted that water  above 18 °C will release CO2 as it warms, but not in the same amounts as cooler water.

Determining the climate sensitivity based on the effect of the cause is backwards and meaningless. Temperature changes CAUSE the CO2 levels to change. There is no evidence that CO2 changes causes temperature change.





Vostok Ice Core: Temperature and CO2.

Northern Hemisphere:  Summer Insolation


Posted in Science Articles - Global Warming by inconvenientskeptic on November 7th, 2010 at 7:59 am.


This post has 12 comments

  1. Richard111 Nov 7th 2010

    Thanks for this. I was going to ask questions but on second thoughts I think this is a lead in to more controversial discussions of feedback effects.

  2. I’m having a little trouble understanding which part of this you think the climate science field has neglected. Yes, of course, the balance of CO2 between the ocean and the atmosphere responds to temperatures, that’s why it’s considered a feedback to the orbital forcing that leads to ice ages. Orbital changes force cooling in high northern latitudes, glaciers grow, temperatures fall, carbon dioxide is taken up by the oceans, temperatures cool further, ice grows in the Antarctic, temperature cool further, co2 decreases further, etc. until the orbital conditions start to warm the Arctic and the whole process reverses. This is all basic stuff from a junior-level climate dynamics class.

    The way one diagnoses climate sensitivity from past climate variations has nothing to do with this. One simply takes a time in the past when temperature was constant for a while (say, the last glacial maximum), notes that this constant temperature implies approximate energy equilibrium, and then looks at the energy budget. The ratio of temperature change to radiative forcing is the climate sensitivity. The radiative forcing is the sum of the change in global average albedo and the change in greenhouse radiative forcing. *Why* the carbon dioxide concentration was lower at the LGM doesn’t enter in to the calculation. Of course there uncertainties in this method. For example, we don’t know the global mean albedo at the LGM exactly. That’s why the estimates of climate sensitivity from paleoclimate come with uncertainty ranges. But if you are going to argue that the method grossly overestimates climate sensitivity to CO2, you’re going to have to come up with better than this.

  3. inconvenientskeptic Nov 8th 2010


    This is part of a very important issue. For example over here they use the change in CO2 to calculate the forcing change and from that they estimate the climate sensitivity.

    The assumption they are making is that the CO2 CAUSED the warming. The article that the one paper cites uses the change in CO2 to calculate the climate sensitivity.

    If the CO2 level changed as an EFFECT of warming oceans, then it is not a CAUSE of the warming.

    The point of this article is to point out that linking CO2 levels to past warming and cooling events has no meaning. The CO2 levels will change as a result of temperature changes. CO2 does not CAUSE the temperature to change.

  4. Richard111 Nov 8th 2010

    From a layman’s perspective I have difficulty understanding the CO2 “forcing” that produces increasing global temperatures. It appears to me that for almost any period of warming the difference in the average surface radiation at beginning and end of said period is divided by the change in the ppmv level for the CO2 over that period and presto! we have a “forcing” that relates to an amount of CO2 increase per degree Celsius warming.
    What happened to cause and effect? There seems to be a gross assumption that CO2 is the cause. So why are we cooling down right now even though global CO2 levels are steadily climbing?

  5. Hi John,

    Wait, now (with the reference you linked to) you’ve jumped away from the ice ages and to the Eocene. At that time, the CO2 change does seem to have been the driving force. Do you have an alternative explanation for Eocene warmth?

    You make the following statement “If the CO2 level changed as an EFFECT of warming oceans, then it is not a CAUSE of the warming”. This would seem to make any kind of feedback cycle impossible. It’s like saying, “if a evaporation of water increases as an EFFECT of tropical storm winds, then condensation of that water is not a CAUSE of the tropical storm.” But of course, everyone knows that evaporation and condensation of water vapor are both a consequence and a cause of tropical storm intensification.

  6. inconvenientskeptic Nov 8th 2010

    Keep an eye out for the Radiative Heat Transfer series. That will slowly get into it. One will be out this week.

    Feedbacks are possible, but the Holocene situation shows that CO2 will naturally increase with warming. The Eocene warming would cause CO2 levels to increase much like any warming of the oceans will. I don’t know what caused the Eocene warming, but stating that CO2 increased and that CAUSED it is not scientific.

    Determining the climate sensitivity from CO2 forcing when it isn’t known what caused the warming is garbage. My point is that warming from another cause would have resulted in the increase in CO2 levels. Cause and Effect are not clear.

    Another example of confused cause and effect is the growth of the ice sheets in Antarctica. 34 million years ago the cooling of Antarctica would have caused CO2 levels to decrease because the oceans cooled around Antarctica. Since CO2 levels are generally accepted to have been 760 ppm at the time, but then dropped as Antarctica cooled. CO2 gets the blame, but really the drop in CO2 was an effect of the cooling oceans.

    The cause of Antarctica cooling was a change in ocean circulation due to a change in geography. Cause and Effect. CO2 is used as a catch all, but there is no evidence that any of the warming or coolings were actually caused by CO2 levels.

    Your storm example is interesting, but not the same. All feedbacks are energy limited. Water vapor evaporating takes energy from the ocean, when it condenses it feeds the energy into the storm and changes the density of the air. That provides pressure gradients that also increase air velocity. It is limited by the amount of evaporation and each additional evaporation limits future evaporation for that storm.

    I do not preclude feedbacks, but the catchall that CO2 gets is absurd. The purpose of this article is to explain that CO2 levels will naturally change with any significant warming or cooling of the Earth. To use CO2 as the cause for everything is foolish.

  7. Richard111 Nov 9th 2010

    Hmm… deep ice ages result in reduced sea levels. Oceans will not absorb CO2 as rapidly as during interglacials. Also how much reduction in sea surface area is due to sea ice?

  8. Hi John,

    CO2 isn’t used as a catch-all. It’s used to explain the Eocene warmth because there are good reasons why it should vary on million year time scales, and because we have solid evidence that it rose suddenly during, for example the Paleocene/Eocene Thermal Maximum. Look, there’s a huge literature out there about this. Have you read any of Berner’s papers on CO2 and climate?

  9. inconvenientskeptic Nov 9th 2010


    If a person believes that higher CO2 is the cause of warmer climate, their work will support that. The Eocene was warm with higher CO2. Every instance of rapid warming was resulted in higher CO2. They do correlate, but one reason they correlate is solubility.

    More interesting to me is that every warming event is followed by a cooling event that occurs while CO2 levels are elevated. So the Earth cools while CO2 is in the very high state. That points to CO2 being a proxy for temperature and not a driving forcing.

    The PETM is a curious event. The energy involved is enormous, but not sustained. Large amounts of bubbling methane didn’t cause it though. Whatever did should be understood. On that we can all agree.

    The oceans lost about the size of North America due to lower sea levels in the last glacial. It isn’t the surface are of the oceans that matters as much as it is the temperature of the oceans. Cold water absorbs more CO2, warm water absorbs less.

    This is seen in the fall/winter in Alaska. The ocean there absorbs lots of CO2 as the temperatures drop. That CO2 gets released in the spring.

  10. Carbon based oxygen can not hurt the environment.

    ~ CO2 caused the environment ~

    Bruce A. Kershaw

  11. David Motry Feb 10th 2012

    I have been trying to find the (oceans) surface area increase per any unit rise in sea level. I do not completely follow all the discussions about gravity, warming/expansion of water but they all seem to be directed at the physical/chemical forces at work in the climate discussion. Nowhere have I seen a discussion concerning the role of plankton in the sequestering of carbon. About 80% of our oxygen is generated by water born life forms. They get this oxygen from the co2 they take up.
    When you increase the sea level, you also increase the surface area. Simple life forms probably do more to keep our planet livable than all the futile attempts to control “man made climate change”. Acts of nature like volcanoes and wildfires probably add more carbon each decade than man has since the beginning.

    Thank you for any information.
    David Motry

  12. inconvenientskeptic Feb 10th 2012


    I will try to answer all your questions.

    First is the change in surface area for a change in sea level. The answer to that is mostly insignificant. The reason for that is the ocean does not behave like a lake. The sea level could change only in the middle of the ocean where there is no coast to compare it to. Most oceans have potions that are increasing and regions that are decreasing. Overall there is no significant change in surface area for a small change in sea level.

    I have discussed plankton and CO2 on this website.


    In that case a volcano dropped iron over a large area of the ocean and triggered a plankton bloom. You can read the article for the details. The effect was minor and proves the idea as basically worthless.

    Mankind is playing a small role in the Earths CO2 level, but each year nature puts many times more CO2 into the atmosphere than we do. The good news is that it doesn’t matter. 🙂

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