A new front in the climate debate – could the observed increase in atmospheric CO2 levels be natural, not man-made?


One of the common elementary errors in scientific analysis is to confuse correlation with causation.  If two phenomena, A and B, are strongly correlated, it is very likely that there is a causal link.  But it doesn’t prove that A caused B.  Perhaps B caused A.  Or perhaps some other phenomenon, C, caused both A and B.  (Timing can be a factor here: if A precedes B in terms of time, we can be pretty sure that B did not cause A).

This particular confusion bedevils a great deal of climate science.  In Al Gore’s famous movie “An Inconvenient Truth”, he demonstrates a close correlation over hundreds of thousands of year between atmospheric CO2 levels and mean global temperatures, and BINGO!  He’s proved that it was CO2 wot dun it.  But he is hung out to dry on the timing issue, because on more detailed analysis the temperature peaks precede the CO2 peaks by around 800 to 1000 years.  If anything, it looks as if temperature drives CO2, not vice versa.

On the face of it, the case for anthropogenic global warming (AGW) is pretty clear.  The level of atmospheric CO2has been increasing steadily as long as we’ve had good records.  This has all taken place during the period since the Industrial Revolution started, with a steady increase in fossil fuel use.  (Leave aside, for the moment, the fact that the current slight warming started well before the Industrial Revolution got into its stride).

Everyone (well nearly everyone) accepts that CO2 is a greenhouse gas, and therefore might have some climate impact.  Challenges to the orthodoxy usually focus first of all on the “Sensitivity” of the climate system to CO2.  Because the theoretical warming effect of CO2 is negative logarithmic, CO2 has to increase geometrically to achieve a linear increase in temperature.  So sensitivity is expressed as the temperature increase resulting from a doubling of CO2 – which (other things being equal) will always be the same.  A doubling from 100 ppm to 200 ppm would cause the same temperature rise as a doubling from 400 ppm to 800 ppm – although the latter involves a four times larger increase.

The climate is so chaotic and the weather so variable that it is quite difficult to decide what the sensitivity might be.  The IPCC likes to work on 3 to 4oC per doubling.  Some scientists believe the figure is much lower.

The other main ground of debate is “feed-back mechanisms”.  For example: warming could increase the level of water vapour, a more powerful greenhouse gas than CO2, so augmenting warming – a positive feedback.  But water vapour results in more cloud cover, higher albedo, less sunlight reaching the earth’s surface, so less warming – a negative feedback.  The IPCC tends to assume that the aggregate of all feedbacks is positive.  Some scientists believe they may be negative.

The failure of global temperatures to increase for the last 18 years, despite continuing increases in CO2, argues for low sensitivity and possibly negative feedbacks.

But although I have been involved in this debate for a decade, it had never occurred to me to question the first link in the chain – that rising CO2 reflects anthropogenic emissions.  I mean, it’s obvious, isn’t it?  Obvious, but maybe not true.

I have often remarked on the 1000 year cyclical pattern of temperature which we have observed for at least ten thousand years.  On that basis, we should have expected a recovery from the Little Ice Age in the 17th century – and that is exactly what we have observed.  It is entirely reasonable to suppose that the observed warming since then would have taken place even without human activity.

The key insight is this: that natural cyclical changes in temperature can themselves drive levels of atmospheric CO2.  The rise we have seen may be partly, or largely, natural and not anthropogenic.  If so, then the vastly expensive measures we are taking to “combat climate change” and to reduce emissions are even more futile than they appear already.  It is worth recalling that man-made emissions are dwarfed by the scale of the natural carbon cycle.  They represent only around 3% of the total.

The mechanism is very simple.  There is an awful lot of CO2 in the atmosphere.  On one estimate, 3000 gigatonnes (3 x 1012). But there is a great deal more in the oceans – again, on some estimates, fifty times as much.  And the relationship between the two is dynamic, not static.

Those who challenge my position on these issues often accuse me (wrongly) of ignoring basic science. Well here’s some basic science they’ve ignored: cool water can hold more CO2 in solution than warm water.  If the ocean cools, it will dissolve more CO2 out of the atmosphere, and atmospheric CO2 levels will drop.  Vice versa, if the water gets warmer, CO2 will be released out of solution and into the atmosphere – raising levels of atmospheric CO2.

It is conceivable that much, or most, of the increase in atmospheric CO2 which we have observed is entirely due to natural causes, in which case our efforts to curb emissions, which already look totally ineffectual, will be even more futile.

There are two objections to this idea, which I expect to be raised by the alarmist brigade.  First, the balance of 12C vs 13C (isotopes of carbon) is claimed to support an anthropogenic/fossil fuel source for the increased CO2.  Second, the current level of CO2 at 400 ppm is higher than that recorded for previous interglacials (by about 100 ppm).  There are satisfactory explanations of both of these points – though they rather go beyond the reasonable bounds of a political blog.  However they are dealt with by Professor Murry Salby of Macquarrie University and the University of Colorado

Professor Salby’s thinking is covered in more detail in a booklet written by Mike Haseler, Chairman of the Scottish Climate and Energy Forum, for The Bruges Group,  “Climate: What we know, and what we don’t”.  I recommend it.  Professor Salby also presents intriguing evidence that CO2 emissions from land surfaces are greatly enhanced by increases in surface temperature and soil humidity – more evidence that temperature drive CO2, rather than the orthodox view, which is the opposite.

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9 Responses to A new front in the climate debate – could the observed increase in atmospheric CO2 levels be natural, not man-made?

  1. ian wragg says:

    A good article Roger but you are wasting your time. The green blob has CO2 as the villain and will stick their hands over their ears shouting La la la to anything contradicting their religion.
    Governments like the climate change agenda as it has become a new taxation stream which they are always looking for.
    At this point in time we have a power demand of 40GW with 4% being supplied by wind which is less than the French interconnector. PV after 6pm when the evening peak is due will be providing 0% but still the government subsidises this rank stupidity.
    Problem is, it has gone on for so long that to admit failure means an awful lot of senior figures and luvvies will be made to look as stupid as they really are.

    • Jane Davies says:

      “Problem is, it has gone on for so long that to admit failure means an awful lot of senior figures and luvvies will be made to look as stupid as they really are.”

      A classic example of the Emperor’s new clothes syndrome!

  2. Ex-expat Colin says:

    BBC Countryfile about 2yrs ago had “researchers” sniffing for CO2 in a wood. Thats at ground level with instruments for that purpose. I think it was John Craven who said it was surprising that 350ppm had been detected. Stony silence thereafter.

    Big bits of the story missing isn’t there?

    • Brin Jenkins says:

      On Sicily, where Etna is always bubbling CO2 is extremely fertile, much more so than Malta only a few miles away. The quality of plants below the tree line on Etna is impressive, this results in bountiful local fruit and vegetables.

      Cold water retaining C02 is the key here as a cause and its effect, heat causes the release of C02, how can CO2 also be the cause of heating? Where this so, positive feedback should have destroyed the eco balance millions of years ago. Anyone understanding feedback mechanisms, knows negative feedback gives stability whilst positive causes instability. Prior to 1939 we used non superheterodyne Wireless receivers (Straight sets) that employed manually variable positive feedback, this was critical, whilst increasing the amplitude gain it could suddenly run wild and go into oscillation wiping out all intelligible data.

  3. Derek says:

    Murry Salby’s lecture seemed very convincing, but, as Ian Wragg says (above) the global warming alarmists are just not interested. Only a cooling of the surface would cause them sufficient embarrassment that their ranks might break.

  4. Anne says:

    The Devil’s Work.

    Soon the Devil’s work be done,
    When Ireland will become as one,
    Devolution has set Scotland free,
    Government for Wales in its Assembly.
    England into nine Regions make,
    Its indomitable spirit must surely break?
    Was “England” such a dirty word
    It had to be divided, as though by sword?

    It was through ‘our own’ by stealth betrayed,
    Yet in our Parliament the MP’s stayed,
    Rubber stamping all EU laws,
    Made in Brussels for one and all.
    A cut in pay? a likely tale.
    A sign to read, “Parliament For Sale”?
    For doing nought, paid long enough,
    The Union now directly would govern us.

    A race once so proud, unique, now gone?
    No Union Jack to proudly look upon?
    For the ring of twelve stars shining on blue,
    Is the flag that will become well known to you?
    Not one MP with the guts to say,
    We’re marching towards the federal way,
    In the name of democracy this deed is done,
    Destroying Nation States, to become just one.

    To divide each country is now the Rule,
    Scotland, Wales, Northern Ireland too.
    For foolish people elected those MP’s
    To try to bring England to its knees,
    Gaze, yet shed no tears for the past,
    For the Union has not been made to last,
    Britain once more will rule the seas,
    Though men have done their heinous deeds.

    England’s flag once more shall fly,
    From the tallest buildings, flown on high,
    The people seek out the fork-tongued ones,
    Though many have sold up and are gone.
    For the emotions of every “Brit” shall soar,
    Their National Anthem loudly sing once more,
    Peace, real truth and liberty shall come to be
    For Britain at long last will be truly FREE.

  5. Chingford Chap says:

    What a well-put, concisely-reasoned argument you’ve made, Roger.
    Like you, I’m a mathematician, I’m also a physicist and stood for UKIP in May’s parliamentary election.
    Unfortunately, Mr Wragg is probably right about the response your article will elicit.
    We could say this is all about density.
    I am not referring to Colin’s anecdote about the BBC, apparently unaware that with CO2 having a molar mass (in g/mol) of about 44, while O2 (21% of the atmosphere by mass) is 32 and N2 (78%) is 28, and with these gaseous standard densities being in those ratios (divide each by 22.4 L/mol to get its SD in g/L), at ground level it will be over-represented. This will be further exaggerated with decaying organic material all over the forest floor.
    No, the density I am referring to is that between the ears of doctrinal Climate Change and MMGW fundamentalists, who miss the wood for the trees as a matter of choice.
    When educating them proves impossible, to wind them up a treat one can try the following: If atmospheric temperature and therefore turbulence dramatically increase, so will evaporation rates from large bodies of water, affected as this is by surface rippling. The surplus H2O, as ani fule kno, ends up as more clouds, which are generally white when viewed from above. This will increase reflectance of solar radiation, and so also the proportion of which escapes into space, thus leading to global cooling.
    This sure isn’t bulletproof, but it is sounder than much of their dogma.🙂

  6. catweazle666 says:

    For example: warming could increase the level of water vapour, a more powerful greenhouse gas than CO2, so augmenting warming – a positive feedback.

    Without a concomitant increase in atmospheric water vapour matching or exceeding the rate of increase of atmospheric CO2 that is postulated by all the AGW models, the high sensitivity water vapour feedback driven catastrophic anthropogenic global warming hypothesis is dead in the water.

    So let’s look at three analyses of NASA’s NVAP atmospheric water vapour satellite data.

    Vonder Haar:




    Solomon et al.

    Stratospheric water vapor concentrations decreased by about 10% after the year 2000. Here we show that this acted to slow the rate of increase in global surface temperature over 2000–2009 by about 25% compared to that which would have occurred due only to carbon dioxide and other greenhouse gases. More limited data suggest that stratospheric water vapor probably increased between 1980 and 2000, which would have enhanced the decadal rate of surface warming during the 1990s by about 30% as compared to estimates neglecting this change. These findings show that stratospheric water vapor is an important driver of decadal global surface climate change.


    So Vonder Haar and Humlum show that atmospheric water vapour over the period of the measurement is trendless, while Solomon et al show an actual decrease.

    No further comment appears to be necessary.

  7. Roger,
    Long ago the BBC had a series of 7(?) programmes presented by Iain Stewart (?). Each of these in turn set out to debunk various reasons being given for ‘climate change’. As an engineer (feedback systems) the first 6 convinced me but the 7th, sunspot cycle and water vapour, did not. But the presenter insisted that that explanation too was tosh and therefore concluded (Sherlock Holmes-like) that warming must be man-made. But he gave no indication of the mechanism involved.

    I do not recall whether it was in this series, but certainly about the same time, I saw the “Inconvenient Truth” graph correlating CO2 and temperature. It seemed that it was upon this relationship that climate change harm was being predicated. But within seconds it occurred to me (as you have separately realised) that the CO2 was lagging the temperature by about 300 years whereas to support his thesis it should have been leading it. This made nonsense of the whole hypothesis. It is that stupidity that has made me a sceptic on the subject.

    Fast forward to last week when I awoke with the thought that if the climate model is valid, it will be able to explain the onset and ending of Ice Ages. Using the Internet to investigate, I find that the cause is uncertain. Scientist will tell you that the proof of a good theory is its ability to predict. If the model, derived from the theory, cannot predict Ice Ages then it has to be invalid or at least incomplete.

    I have read comments about the under-estimating of the effect on atmospheric carbon of trees. These provide nature’s own carbon capture and storage (CC&S). 1000 years ago the South American forests were but a pale shadow of them now. Archaeologists there are finding evidence of civilisations overgrown by forests, clearly not there at that time. As trees absorb ‘carbon’ they denude their food source. This is a negative feedback, self correcting, system. In the 50s I was taught about this as the “carbon cycle”. If man comes along and liberates fossil ‘carbon’ the trees have more food and grow to a new stable level. Reported here of the beneficial growth below volcanoes illustrates the point. Water also has an input to this balance.

    Tree-huggers, for ideological reasons, want to blame mankind and his Industrial Revolution for the CO2 rise but during that period rain-forests would have been absorbing the fossil carbon. With the invention of the ICE the use of petrol has greatly accelerated the emission of fossil ‘carbon’ into the atmosphere but nature’s CC&S (rain-forests) should, over time negate the effect and grow more vigourously. Photos of the Cotswolds then and now support this notion! I have not seen any evidence that climate scientists have factored this mechanism into their model.

    But now consider the effect of reducing the amount of tree cover by deforestation (as has occurred). The amount of carbon that can be absorbed by the trees is reduced so the level in the atmosphere will rise because there are fewer trees left to capture man’s’ fossil carbon emissions. Worse still if the carbon is burned to make room for prairies this adds to the emissions. Under these circumstances it would not be surprising for atmospheric ‘carbon’ levels to increase. Thus if there is any component (not the main cause) for temperature rise from the greenhouse effect it has to be from deforestation. Politicians should resist any attempt to curb man’s activity in this respect to other than deforestation.

    It would be an interesting exercise to compare the amount of carbon liberated from the extraction of fossil fuels to the bulk increase in wood and other long lasting vegetation over the last millennium.


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