The blog THE HOCKEY SCHTICK claims that "temperature drives CO2 levels, not man-made CO2".

The paper "Atmospheric verification of anthropogenic CO2 emission trends" is cited as proof.

The claim is detailed as follows:

A recent paper published in Nature Climate Change finds a disconnect between man-made CO2 and atmospheric levels of CO2, demonstrating that despite a sharp 25% increase in man-made CO2 emissions since 2003, the growth rate in atmospheric CO2 has slowed sharply since 2002/2003. The data shows that while the growth rate of man-made emissions was relatively stable from 1990-2003, the growth rate of atmospheric CO2 surged up to the record El Nino of 1997-1998. Conversely, growth in man-made emissions surged ~25% from 2003-2011, but the change in the growth rate of atmospheric CO2 has flatlined since 1999 along with global temperatures. The data demonstrates temperature drives CO2 levels due to ocean outgassing, man-made CO2 does not drive temperature, and that man is not the primary cause of the rise in CO2 levels.

The prominent website SkepticalScience defends the assertion that CO₂ levels drive temperature despite lagging but does not seem to provide a clear explanation as to why yet provides this graph of carbon dioxide vs temperature:

enter image description here

SkepticalScience does seem to explain the temperature oscillations by the Earth's orientation relative to the sun:

enter image description here

but the explanation for changes in CO₂ causing changes in temperature despite lagging temperature is unclear.

Is it true that temperature leads and drives CO₂ levels? Why or why not?

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    Note that the quote from the blog reveals the error; they say that temperatures have flat lined since 1999, however if the rise in CO2 was temperature driven, CO2 levels would have stopped rising as well since 1999, but they clearly haven't (esrl.noaa.gov/gmd/ccgg/trends). Their error is conflating the rate of growth of CO2 with the growth of CO2. This is the same error made by Prof. Salby (an others before him), see skepticalscience.com/salby_correlation_conundrum.html for an explanation of this error. – Dikran Marsupial Jun 25 '14 at 17:59
  • @DikranMarsupial The graph appears to show that carbon dioxide tends to experience wide lags when temperature drops; although this looks like the first time that CO2 looks to be rising while temperature is falling, so is it possible that anthropomorphic production of CO2 is adding to atmospheric CO2, yet temperature is falling anyways? – user20862 Jun 28 '14 at 2:25
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    if you don't understand the SkS article, then please ask a question there and I will do my best to deal with it. This forum is not set up for discussions, just providing definitive answers to specific questions. My answer shows that the rise in CO2 is 100% anthropogenic, and does not substantially depend on temperature. The reason for the lag in paleoclimate data is that it takes time for the Milankovic forcing to warm the oceans (the land warms up more quickly). As the oceans warm, they release CO2 as the solubility drops. This causes CO2 to increase in the atmosphere... – Dikran Marsupial Jun 28 '14 at 14:53
  • ...which causes further warming. This further warming further warms the ocean (with a delay due to its enormous thermal inertia), and so on. Fortunately CO2 radiative forcing is logarithmic, which is why the positive feedback doesn't lead to a runaway greenhouse effect. The delay between temperature and CO2 is because CO2 is acting here as a feedback mechanism, and the CO2 is only released by the oceans after the thermal inertia of the oceans has been overcome. Modern climate change is different, here CO2 is not being released as a feedback mechanism, we are transfering it directly from... – Dikran Marsupial Jun 28 '14 at 14:56
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    I have already explained that the behaviour seen in the ice core data is irrelevant because carbon is being put straight into the atmosphere by fossil fuel use, rather than being a feedback response to changes in temperature (which is what is seen in the ice cores). It isn't as simple as being one thing or another. Temperature affects CO2 (e.g. via Henry's law) and CO2 affects temperature (greenhouse effect). However temperature is not the only thing that affects CO2, there is also e.g. fossil fuel use. However, the mass balance argument clearly... – Dikran Marsupial Jun 30 '14 at 11:29

The idea that "global temperatures cause the increase of CO2." is fairly easily refuted. The line of reasoning is that the solubility of CO2 in water decreases as temperature increases, so the rise in global temperature implies that the oceans will have released some of the dissolved CO2 that it contains. The premise is correct, but the conclusion is a Non sequitur as it ignores the fact that the solubility of CO2 in water also depends on the difference in partial pressure of CO2 between the ocean and the atmosphere. As we have released CO2 from fossil fuels into the atmosphere, the partial pressure of CO2 in the atmosphere has risen, and so the oceans have been taking up more CO2, not less.

How do we know this is true?

The argument is easily refuted by the observation that the rate at which atmospheric CO2 levels are rising is less than the rate at which we are releasing CO2 into the atmosphere from fossil fuel use, which implies that the natural environment must be a net carbon sink, taking in more carbon each year than it emits.

More formally, let Ea represent annual carbon emissions from anthropogenic sources (fossil fuel use and land use change), En represent the carbon emissions from all natural sources (the oceans, soil respiration, volcanos etc.) and Un represent the uptake of carbon by all natural carbon sinks (oceans, photosynthesis, etc.), Ua would be the uptake of carbon due to anthropogenic activities, but this is essentially zero, so we can safely exclude it from the analysis. Then assuming that the carbon cycle obeys the principle of conservation of mass (any carbon emitted into the atmosphere that is not taken up by natural sinks remains in the atmosphere), the annual change in atmospheric CO2 is given by:

C' = Ea + En - Un

This can be rearranged to give an estimate of the difference between annual emissions from all natural sources and annual natural uptake by all natural sinks.

En - Un = C' - Ea

We have accurate, reliable data for the growth of atmospheric CO2 and for anthropogenic emissions (for details, see Cawley, 2011). Both of these are displayed below, along with an estimate of the net natural carbon flux En - Un. The fact that the net natural flux is negative clearly shows that natural uptake has exceeded natural emissions every year for the last fifty years at least, and hence has been opposing, rather than causing the observed rise in atmospheric CO2.

enter image description here


Some time back, I wrote a journal paper refuting a related climate myth, which outlines some of the evidence that the rise in atmospheric CO2 is anthropogenic, and is not a natural phenomenon.

Gavin C. Cawley, "On the Atmospheric Residence Time of Anthropogenically Sourced Carbon Dioxide", Energy & Fuels, volume 25, issue 11, pages 5503–5513, 2011.

I find it hard to understand how this argument can be so ubiquitous on climate blogs, given that it is so easily refuted. For further information, see the many articles on SkepticalScience.com addressing this issue (and other climate myths).

N.B. I gave this as a tangentially relevant answer to a related question. It is more directly relevant to this one. The following is new:

The reason usually given for temperature driving CO2, rather than the other way round is Henry's Law, which says that the solubility of a gas in a liquid is proportional to the difference in partial pressure of the gas in the atmosphere and the concentration in the liquid, and that the constant of proportionality depends on temperature. The argument goes that ocean temperatures have risen, which means that the constant of proportionality has changed and thus the oceans will begin degassing. However, this ignores the other part of Henry's Law. Anthropogenic CO2 emissions have increased atmospheric CO2, which has increased the pressure differential, which in turn increases the solubility of CO2, and the oceans become net carbon sinks. The question is, which wins out, the temperature driven degassing or the partial pressure difference driven uptake? We can be very confident that the oceans are not a net source of CO2 as (i) the mass balance indicates the natural environment is a net carbon sink, if the oceans were a net source, the biosphere would need to be an unfeasibly large carbon sink for there to be conservation of mass and (ii) the oceans are becoming more acidic, which is what you would expect if it were a net carbon sink.

Another line of argument is given by looking at the changes in atmospheric CO2 between glacial and interglacial periods, which suggests that we should expect to see only about 8ppmV increase in atmospheric CO2 per degree of warming. We have seen an order of magnitude more, which means that Henry's law (even ignoring the change in partial pressure due to anthropogenic emissions) cannot explain both the current rise in CO2 and these prehistorical increases.

As to why CO2 lags temperature on a long timescale, the Skeptical science link given in the question seems to explain it pretty well. As to short term correlations between CO2 and temperature, these are likely due to ENSO (El-Nino), which causes changes in both temperature and precipitation in the Americas. These in turn cause changes in vegitation growth and die back and as a result, changes in the rate of growth of CO2. This was notices by Bacastow back in the 1970s (see also Jones et al.). Note I emphasised rate of growth of CO2. The long term rise in CO2 depends on the average value of CO2, the interanual variations in the rate have almost no effect on the long term increases. This is an error that Prof. Salby makes in the talk he gave to the Sydney instritue, and my explanation of this (slightly complex) error is given here.

I can't do much more today, I'll try and add some more references later, however my Energy and Fuels paper contains enough information to show that the conclusions of the blog article are incorrect (I wish they weren't!).

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    The one I gave is a peer reviewed journal paper that I wrote that directly addresses this argument in detail. Adding additional references will largely be just repeating the information contained there. The paragraph on Henry's law doesn't need anything more than a Wikipedia reference as it is basic physics. What specifically do you consider needs referencing (I've added the Bacastow reference). – Dikran Marsupial Jun 28 '14 at 14:41
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    @vartec not assumed, but inferred. It is what you get if you combine the things we can measure with good accuracy (atmospheric CO2 and anthropogenic emissions) with the very reasonable assumption of conservation of mass (i.e. the carbon cycle is a closed system and carbon is not spontaneously created or destroyed in significant quantities). Essentially the point is that if both mankind and nature were net sources of carbon into the atmosphere, then atmospheric CO2 would be rising faster than anthropogenic emissions. The fact that it isn't means that cannot be the case. – Dikran Marsupial Jun 30 '14 at 15:45
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    @vartec The error bars on both sets of measurements are much too small to affect the conclusions, we would have to get anthropogenic emissions wrong by a factor of two before there were any evidence that the natural environment was a net source. This is clearly unreasonable as governments keep very good figures on fossil fuel use for taxation purposes. The measurements of atmospheric CO2 are known with even higher accuracy. Inferring quantities that you can't measure directly in this way is pretty common in science. – Dikran Marsupial Jun 30 '14 at 16:37
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    Consider this example: Say I put $1000 dollars a month into a joint account (which has no fees, no interest) that I hold with my wife (and which nobody else can access), and take nothing out. The balance rises by $500 a month. Your argument is a bit like saying that I can't infer that my wife is taking $500 a month more out of the account than she is putting in, without actually measuring her deposits and withdrawals. I don't have to do this as knowledge of my transactions and the balance allows me to infer her net contribution to the balance. – Dikran Marsupial Jun 30 '14 at 16:41
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    @vartec As I pointed out, while Ea is an estimate, we can be very confident that we have no overestimated fossil fuel use by 100%, and even then that only brings us to the point where the natural environment has a neutral net effect on atmospheric CO2 (taking in exactly as much as it emits). Ea is also based on measurements as the amount of fossil fuel extracted and used is measured. Note that Prof. Salby (who reintroduced this line of argument back into the climate debate) explicitly said that the emmissions data are reliable in his Sydney Institute talk. – Dikran Marsupial Jun 30 '14 at 16:51

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