The absurdity of a 4 degree Celsius rise in temperature

A four degree Celsius rise in average global temperature in the 21st century was put forward some months ago by the World Bank, without any serious scientific argument that I could find, and it has resurfaced in Australia recently, in a book by Peter Christoff of the University of Melbourne (Four Degrees of Global Warming: Australia in a Hot World). I thought it was classic scary stuff, and decided to pass it by. But he is now writing about it on The Conversation, where it is being vehemently defended by the faithful. And of course it had a run on the ABC.

What has to be said about this scare is that it is hard to see how the 4 degrees C can occur. A few years ago those worried about warming  pointed to the similar trajectories of atmospheric carbon dioxide accumulation and temperature rise, and told us that these would continue until we did something about carbon dioxide emissions. Now that there has been a halt in temperature globally, they have moved the goalposts, stating that this warming will kick in with a vengeance after 2050. How do they know? Their models tell them so.

As I pointed out recently, someone has calculated that at the present almost imperceptible rate of warming it will take 800 years before we get to 2 degrees Celsius above the present. And of course I don’t seriously suggest such an outcome. What we know of warming in the 150 years since we have had some reliable measuring instruments in at least a few places, is that warming and cooling seem to occur in phases. Maybe CO2 has an influence, but the current stasis tells us that the natural phases or cycles (or whatever makes up natural variability) are powerful enough to mask that effect.

Professor William Happer of Princeton has sent me (and others) an email setting out a straightforward calculation based on IPCC figures, and I thought I’d arrange the argument for those who might find the calculations hard going. The core of the IPCC argument is the formula

required CO2 concentration = C = C0 x 2^(DT/DT2) where C0 is the current concentration (C0= 400 ppm), DT is the temperature rise resulting from concentration C, and DT2 is the (disputed) temperature rise for doubling.

The IPCC is asserting that mean global temperature will increase as carbon dioxide concentrations increase, according to a ‘climate sensitivity’ factor, which it sees as producing a 3 degree increase in average global temperature for a doubling of carbon dioxide.

Happer thinks the climate sensitivity figure is too large, and so do I. But let that pass for the moment. If we accept it, and then ask — what is the level of carbon dioxide that would be needed to produce a 4 degree rise in temperature from today? — the answer we would get, using the IPCC formula, would be 1008 parts per million. Today’s level is around 400 pp, which means we would need to have increased the level of carbon dioxide in the atmosphere by more than 600 ppm.

This has to be fantasy stuff. The level of CO2 goes up at about 2 ppm each year, and the biosphere gratefully accepts as much of it as it can. To get to 1008 ppm, at the present rate, will take more than 300 years.

Most of the recent estimates of ‘climate sensitivity’ hover around the 1 degree Celsius figure (that is, a doubling of CO2 provides a warming increment of around 1 degree C). If we put that value into the equation it will take 3,000 years to get to the required level of carbon dioxide. Those who study the Earth’s fossil fuel reserves doubt that they are large enough, even if we were able to use all of them, to produce such a level of carbon dioxide in the atmosphere.

In short, Christoff’s argument doesn’t make sense. As far as I can understand what he has done, he has simply accepted the possibility of a 4 degree warming, and then gone into warning, doomsday mode: here’s what we must do, and we must do it yesterday, and all of you — yes, you too! — have to take part…

Why do people take this sort of stuff seriously?

Join the discussion 25 Comments

  • Malcolm Miller says:

    People are very gullible, or else religions would never have taken such a hold. Climate fear is a religion, with its own priests and churches, but luckily the followers are only a very noisy minority. Most of us simply ignore their ravings.

    • Don Aitkin says:

      But governments committed themselves to the fear some time ago, and it is hard for them to say they were wrong.

      • BoyfromTottenham says:

        Hi Don,

        I wish to make three points – (1) the CSIRO/BOM document says “Projections” not “Predictions”. A projection is merely the artifact of some (unverified) AGW model, and therefore in scientific terms means zilch. (2) the document initially quotes the range of 0.2 to 0.4 degrees (of projected warming by 2070) in varying locations across Australia, but then seems to assume (or allow the lay reader to assume) that the whole country will be affected to the same extent, which is unlikely if the map showing historical warming is to be believed. (3) Most importantly, the science that I have read indicates that the relationship between atmospheric CO2 concentration and AGW is Logarthmic, not linear, and therefore each increment of CO2 above the baseline figure of 300 – 350 ppm will have a rapidly decreasing warming effect. Unfortunately most warmists conveniently forget this scientific fact, and resort to misleading linear extrapolation to come up with their scary “projections”, which the lazy MSM change to “predictions” when they are no such thing. This to me indicates (at least) two layers of “disinformation” that is being perpetrated on the lay reader by these disingenuous warmists and their camp-follower journos. I suggest that readers look up the definition and history of “disinformation” to get a clearer picture of the way that the public is being misled, frightened and confused by this deliberate strategy.

        • David says:

          Boyfrom Tottnam,

          It probably won’t surprise you to know that I don’t agree
          with much of what you have written. 🙂

          Point 1: Is spurious.

          Point 2: Correct, temperature will vary.

          Point 3: Is amusing. Here we have someone sharing their special insights on the functional form of the relationship that they don’t believe in. So, which science tells you that the relationship between CO2 and temperature is log? This claim is not out of the question. But unless you have some good
          theoretical reason to support this claim all you are doing is “curve fitting”.

          • BoyfromTottenham says:


            Thanks for the response, but I disagree with your comments as follows:

            Point 1 is spurious – well, I can’t help it if you choose to pretend that two defined words (projected and predicted) with distinctly different meanings are equivalent.

            Point 3 – I refer to the results from the Modtran atmospheric radiative model, developed for the US Air Force and extensively validated (see:, which clearly shows the logarithmic response:

          • David says:

            On your vertical axis, you have “Net downwards forcing”. AGW
            is about a relationship between CO2 and temperature. On your horizontal axis, you have CO2, well done. But on your vertical axis you need to have temperature, obviously!

  • David says:

    You write
    “As I pointed out recently, someone has calculated that at the present almost
    imperceptible rate of warming it will take 800 years before we get to 2 degrees
    Celsius above the present. And of course I don’t seriously suggest such an


    In this post you wrote

    “At the present rate of warming, someone has worked out, that 2 degrees target is 800 years away.”

    Without qualification this was immediately followed by

    “So my position, like that of the reader, is that the science is immature.”

    Seems like you accepted this claim from your special “someone” at face value to me, Don.

    • Don Aitkin says:

      No, David, it’s just simple arithmetic. Someone tells us that we must ensure that average global temperature does not rise above 2 degrees C from the present. Anyone can work out how long it would take to reach that level, given the current rate of temperature increase, which is hardly an increase at all. It’s much the same as the point Professor Happer is making: if there is to be a 4-degree increase, what is the level of CO2 that would be needed to produce such an outcome, using the IPCC’s own formula? It is not hard to work out, and the result makes it clear that these scares, given our present knowledge, are a long way off, if they are real at all.

      ‘Climate science’ is immature, and its projections about the future need to be given close examination.

    • David says:


      So you are back to supporting the “800 years before we get to 2 degrees” statement? Your flip-flopping on this issue is hard to keep up with.
      I would not describe temperature prediction as easy, at all. The annual rate of temperature increase, changes from year to year. That’s the whole point of the AGW 30 year debate!.

      • Don Aitkin says:

        I’m sorry to say that you don’t appear to see what the arithmetic reveals. If CO2 is the real control knob, then the amount of CO2 must be pivotal, and even with the IPCC’s own climate sensitivity measure, we won’t be there for a very long time.

        • David says:

          I am not taking issue with the “arithmetic”. You don’t present any.
          My issue is with the way your construct your argument. My point is that sometimes you have bought into the ” it will take 800 years to facilitate a 2 degree increase in global temperature” and elsewhere you disown it.

  • David says:

    You describe a 4 degree rise in global temperature by 2100 as absurd and then lament you inablility to find an serious scientific argumen to support this perdiction.

    Anyway after a about a 30 second serach on Google I found this publication jointly publiched by CSIRO and the Australian Bureau of Meterology in 2010.

    In this publication they predict temperature rise for Australia of between 2.2 and 5 degress by 2070. The mid point of whiich is 3.6 degrees.So in my view your characteriseation of prediction of a 4 degree rise for the globe by 2100 as absurd was a bit intemperate!


    • Don Aitkin says:

      All I can say is that those who wrote the article didn’t ask themselves what level of carbon dioxide would be necessary to produce such an outcome, if the IPCC’s account of things were in fact true (I think the IPCC’s climate sensitivity figure is too high). If they had done the arithmetic they must have said to themselves that this outcome is extremely unlikely.

      • David says:

        So why don’t you write something like that I the first place, instead of referring to the scientific propositions proposed by organizations like the CSIRO and the BOM as absurd?
        Would it be so hard to be polite?

        • Don Aitkin says:


          I’ve read the paper you referred to. There is no evidence that the authors paid any attention to the likelihood of what they proposed. Their c.s. estimates seem to be drawn from the IPCC 4AR. Nowhere in that document either is there any consideration of how much CO2 would be needed.

          My reference to ‘absurd’ was not to the CSIRO/BOM paper but to both the World Bank report and Professor Christoff. Don’t you think it is at least extraordinary that neither looked to see just what would be involved in a 4-degree rise?

          • David says:

            “Nowhere in that document either is there any consideration of how much CO2 would be needed.”
            That is an interesting question. What you are asking goes to the heart of the debate. I would have thought a good answerer to that question would delve into to some pretty dense climatology.
            Of course if we knew precisely how CO2 effected temperature we would not need statistics. Statistics was invented to deal with uncertainty.
            What you and I talk about is mainly statistical methods.

      • David says:

        “If they had done the arithmetic, they must have said to themselves that this outcome is extremely unlikely.”

        They obviously have done some “arithmetic”. Assuming a normal distribution of predicted temperatures, when the CSIRO or BOM puts out predicted temperature range, of 2.2 to 5 degrees, what they are saying is that is that a rise of 2.2 degrees has an equal probability as a 5-degree increase And that the 5-degree rise is more likely than a zero degree rise.

  • Peter Kemmis says:

    It seems to me to be the same presumption offered before, that we’ll see a 4 degree rise. In March this year I attended a public lecture hosted by the Centre for Climate Economics and Policy and the Development Policy Centre of the Crawford School of Public Policy at the ANU. The topic? “Climate change: Avoiding a four degree warmer world”, presented by a Rachel Kyte, VP of the Sustainable Development Network, World Bank. The presentation was preceded by a short climactic video clip, with the usual panoramas of drought and famine. The presentation complemented the clip quite nicely. No discussion of the assumptions, of course – there never has been at any of those gatherings that I’ve attended over the last eighteen months.

    As the evidence for catastrophe drops away, two things seem to happen; the voices become more strident with alarm, and if that fails, the goal posts, as you say, are shifted.

  • […] I came across the Christoff post in The Conversation, which I referred to yesterday, I was struck once again by the poor quality of the arguments in the comments section. What I found […]

  • davids99us says:

    Don – thank you for a very good blog post. I particularly like the use of mathematics that is basic; it makes the argument both rigorous and accessible to the most number of people. Even Einstein made his mathematics simple to the specialists of the day, and so was more convincing. Showing that state-sponsored articles like the SoC contradict basic maths or observations (including their claim of no increase in rainfall) has been quite effective at derailing the AGW juggernaut. Telling the reader how to think about things – must include how to think about things in mathematics they understand.

    • David says:

      What Einstein actually said “everything should be made as simple as possible, but no simpler.
      Its that second phrase which can make things a bit tricky 🙂

  • David says:

    National Climate Assessment NASA have published a predictions for CO2 in 2100 in the range which from 550 ppm to 800ppm and corresponding temperature increases from 2.2 C to 4.4 C.

    1. NASA has NOT simplistically assumed that CO2 will increase linearly, at a rate of 2ppm per year, as you have done! A level of 800 ppm would be a doubling of the current level in 100 years.

    2. The formula Prof Happer emailed you is not in dispute. Both sides of the debate accept it. The whole AGW debate surrounds the extent to which this and other models can explain the changes in the climate we may observe.

    3. Christoff’s working assumption of a 4C increase lies within NASA’s estimates.
    So it seems reasonable to me. I certainly would not characterize it as absurd!

    • Don Aitkin says:

      There is no obvious acceleration in the rate of increase in CO2 in the atmosphere. Why should we assume that it will rise later? Some argue that the more there is the more the biosphere will greedily lap it up.

      • David says:

        Well I can think of a couple.!

        Intuitively you should be able to see that if GDP was to grow
        steadily at x% then in absolute terms (e.g. kilojoules) an input like energy may need to grow to grow exponentially to keep up with the compounding effect of x% growth rate in GDP.

        Population has grown exponentially in the past, and expected to do so for a while yet, so don’t you think people’s energy needs will follow a similar growth pattern.

        The aim of my post is not to defend ever single assumption
        that NASA has made in their climate models. But rather to make point that Christoff’s estimate a 4 degree increase by 2100 is not absurd. In fact it is within the range of estimates published by NASA.

        • Don Aitkin says:

          Population is not increasing exponentially, as the rate of increase is declining. We do not know how much CO2 the biosphere will take up, but it seems to have kept up its use as the amount has increased.

          I still think it is absurd that those who propound such a temperature increase do not look to see what level of CO2 would be needed to sustain such an increase (given the assumptions), and what would be needed to produce such an amount of CO2.

          Biut I’m happy to agree that we disagree.

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