CO2 and Global Temperature

The basic idea behind global warming is that CO2 is one of the main (if not the main) variables that dictates the temperature of the Earth.  This is so prevalent that when a researcher says that the CO2 levels are at the highest level in 15 million years, it makes the news.  Somehow there is the perception that a certain CO2 level somehow causes a certain temperature.  This is of course ridiculous.

The idea from this is based on the bad science idea that correlation equals causation.  With that idea in mind the worst and most misleading chart of all time is the one made famous by Al Gore.

The Inconvenient Skeptic

Common CO2 and temperature correlation chart.

The reason it is so misleading is because it gives the impression of a correlation, but doesn’t actually provide any information.  I am going to correct that little problem.

To start off I am going to provide the warmist view that if CO2 levels had never risen above 280 ppm from 150 years ago, the Earth’s temperature would be 0.8 to 1.0 °C cooler than they are now.  So the temperature anomaly based on the zero anomaly would be about -0.5 °C.  Depending on which temperature set a person uses that might vary a little bit, but hopefully no one will argue that idea too much.

So the CO2 level to temperature correlation is about 280 ppm to -0.5 °C.

With that in mind let’s look back to the Eemian Interglacial that took place from 135,000 to 115,000 years ago.  If you look at the chart above that is based on the Vostok ice core data.  The Vostok uses hydrogen isotope data (instead of the more common oxygen isotope) as the temperature proxy data and trapped air bubbles in the ice for the CO2 data.   If I take a closer look though, the results are rather different from what a person would expect.

The Inconvenient Skeptic

(Red) Vostok CO2 data, (Tanish) Vostok Temperature Proxy

According to this, the CO2 level of 280 ppm correlates to 2-3 °C.  So according to the very famous chart that shows CO2 determines temperature, the same level that 150 years ago meant the Earth should be -0.5 °C, meant that the Earth should be 3.0 °C warmer.  Same chart, same source, two very different results.

If one were to extrapolate the temperature from from the 2.5 °C warmer and apply the IPCC forcing and climate sensitivity values, then the Earth should be almost ready to boil (or ~4 °C for the modern anomaly).  It is interesting that the projected IPCC warming matches what the Earth was like when the CO2 level was at the natural 280 ppm.

Of course, the Vostok temperature is not the really good temperature reconstruction from the Eemian.  The really good one is the EPICA temperature reconstruction.  Unfortunately  the CO2 doesn’t cover the entire period, but it does cover about half of it.  So I will show both the EPICA and the Vostok CO2 level with the EPICA temperature reconstruction.

The Inconvenient Skeptic

(Red) Vostok CO2, (Purple) EPICA CO2, (Green) EPICA hydrogen isotope.

The EPICA CO2 level peaks right at 290 ppm, with a temperature anomaly of 4-5 °C.  So if CO2 levels to determine temperature, then the Earth is really, really in lots of trouble.  Of course, the Earth was hotter than the IPCC projections for doubling CO2 when the CO2 level was a mere 290 ppm.

In fact, if the CO2 forcing and climate sensitivity of 3 °C/doubling is correct, then the Earth should not be 5 °C until the CO2 level is ~900ppm.  The problem is that a careful analysis for the fundamental chart of global warming shows that 5 °C happens when the CO2 level is more than 3 times lower than 900ppm.

Once again the theory of global warming runs into another inconvenient fact.  The past CO2 levels to not match up with the projections of the IPCC.  The Earth was much warmer with lower CO2 levels in just the last interglacial.  It isn’t just the last interglacial that doesn’t match up with the theory of global warming.  The interglacial from 335,000 years ago shows more of the same.

The Inconvenient Skeptic

(Red) Vostok CO2, (Tanish) Vostok Temperature reconstruction using hydrogen isotope values.

The closer one looks at the idea, the less the idea the CO2 levels dictate the temperature make sense.  The Earth has been warmer with lower CO2 levels in the recent past.  It isn’t that one record doesn’t match up, it is that all the records don’t match up.

CO2 at best was a vague, but poor proxy for ocean temperature.  The worst thing that CO2 emissions have done is make it a worse proxy than it was before.  The paleoclimate data provides no evidence that it is the Earth’s thermostat.

Posted in Bad Science and Climate and Fear and Misinformation by inconvenientskeptic on March 31st, 2011 at 3:50 am.


This post has 7 comments

  1. intrepid_wanders Mar 31st 2011

    Another fun dataset is the Fuji Dome. There is a “Wet CO2” and a “Dry CO2” set. The Wet Set strikes me to be to be the original work and Dry set is just a smoothing of the Wet.

    Anyhow, the data whispers to me that there is an equilibrium process that is moving to 8-10 degrees *lower* than current temperatures and some process every 100,000 years, or so, kicks the *power* or heat function on. I would not be surprised if the CO2 drifts low with no apparent reason, liken to the behavior of the polar ozone levels.

  2. Richard111 Apr 1st 2011

    My suspicion is that CO2 levels follow temperature and LIFE levels. That means ALL life. Microbes kilometres down under rock and even deeper under the sea and up on the land. Us humans are indeed messing with life with our farming and fishing practices not to mention our rate of breeding. So its not just the burning of fossil fuels changing CO2 levels. I also believe that by increasing a highly radiative gas in the atmosphere we improve the ability of the atmosphere to COOL itself by radiation to space.
    A cooler atmosphere will be effected by larger temperature gradients around the globe increasing wind speeds and weather events.
    Also a cooler world will require more energy to help us poor humans survive which will produce more CO2.
    So it looks to me the real problem is population and the desire to control or restrict the rising population is the driving force behind the AGW hysteria.

  3. Alan D McIntire Apr 4th 2011

    Volcanoes have been pouring CO2 into the atmosphere for 4.6 billion years. I read in a geology book that at the current rate of volcanic CO2 injection into the atmosphere, CO2 would double every 20,000 years or so- a drop in the bucket compared to 4.6 billion years. Presumably the volcanic activity is influenced by the heat in the earth’s core. 4.6 billion years ago the earth had roughly twice the U238 it has now, so presumably volcanic CO2 injection was higher then, and has been falling off ever since as the earth cooled. Obviously there are significant negative feedbacks limiting the fraction of CO2 in the atmosphere.

  4. inconvenientskeptic Apr 4th 2011


    There are many sources of CO2 into the atmosphere.

    The source of CO2 almost doesn’t matter though. The oceans and plants absorb enormous quantities of CO2 every year. It is a vast equilibrium that is comparable to the Earth’s water cycle.

    Short term effects like volcanoes and emissions are nothing compared to the importance of the oceans temperature. As the ocean gets cooler, CO2 levels drop. when the ocean warms, they go up.

  5. Right, short term effects mean nothing if your time scale is millions of years. However, most of need to be concerned about the next decades, centuries and millenia (millenia only if we care about the fate of humanity). Over those time scales, what humans are burning is the dominant factor in atmospheric CO2.

  6. Charles Higley Apr 16th 2011

    Of course, there is the work of Ernst Beck (“180 Years of atmospheric CO2 Gas Analysis by Chemical Methods”) that show that CO2 has been significantly higher than now during three periods of the last 220 years. The most recent period was in the 1940s, at 440-550 ppm CO2 (only 390 ppm now), and temperatures crashed while CO2 was high, showing that CO2 cannot maintain a warm climate let alone cause one.

    Of course, the IPCC discounted most of the papers gathered together by Beck saying that their data was “too variable” (they wanted consistently low for the historical past because that was what they wanted and needed) and only recognized two papers. They lauded two papers by French researchers who used a CO2-sulfuric acid assay method that is well know for underestimating CO2 concentrations. That’s the IPCC, always selecting only the data that suits them. Then they took Callendar’s data and cherry-picked points that were low, creating an artificially low average which they then pretended to be a scientific fact. They lied.

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