What would need to happen for me to agree that global warming has been caused by humans and is a real danger to humanity?

A reader asked this question, and I thought it was fair and that I should answer it. I’ve been asked it before but until now only at question time after a talk. Several years ago I gave such a talk at the Planning Institute of Australia, and in it I set out the basic AGW proposition like this:

Human activity in burning coal and oil, and clearing forests has, over the past century, put an enormous amount of carbon dioxide into the atmosphere where it has combined with water vapour and other gases like methane to increase global temperatures in an unprecedented way. The evidence that this has occurred is clear-cut, and the increase in temperature will have, according to our computer models, dire effects on the planet, causing the melting of polar ice, the raising of sea levels, droughts, floods, storms and desertification. We must put an end to this prospect by changing our way of life lest catastrophe strike us. It may already be too late.

The rest of my talk, which you can read here, was an examination of each aspect of the AGW proposition, using the evidence that was currently available, including that in the IPCC’s AR4 of 2007. I have said recently somewhere that the evidence that has come available since 2007 makes me even less prepared to accept the AGW scare, but that doesn’t answer the question in the title. So here goes.

1. That the earth has been warming over the last century. I think that this is very likely to be the case. Temperature data are rubbery, and the uncertainty increases rapidly the further back we go. But I think that I would agree that the earth has warmed, in fits and starts.

2. That the warming is unprecedented. Compared to when? At present I think the evidence points to earlier warming periods in human history, conventionally called the Mediaeval, the Roman and the Minoan Warm Periods. I would be more interested in the AGW scare if there were very strong evidence that the present period is significantly warmer than these eras.

3. That the warming is strongly amplified by water vapour and clouds. This is a necessary element of the scare, because radiative physics says that doubling the carbon dioxide proportion in the atmosphere will, other things being equal, lead to an increase in temperature of about 1.1 degrees Celsius, and that the increase is logarithmic. If we go back to the start of the Industrial Revolution, when the CO2 proportion has been estimated at 280 ppm, then a doubling would be to 560 ppm, and most of the increase will have already occurred. In short, there is a while to go before we get there. The orthodox use a notion called ‘climate sensitivity’ to argue that water vapour and clouds will amplify the ordinary increase by many times, which could lead to an increase in temperature of perhaps 6 degrees C. There is no observational evidence, or laboratory experimentation, that supports any particular amplification, and estimates of the amplification range from less than 1 through neutral to large numbers. I would take the AGW scare much more seriously if it could actually be shown that the amplification was of the order of, say, three times.

4. That human activity has been responsible, or largely responsible, for the warming we have been having. This is probably the key element in the AGW scare, and the orthodox have been trying for more than twenty years to nail it down. In the beginning it was sufficient to point to the correlation between rising CO2 levels and rising temperature. But after 1998, and the failure of temperature to keep rising, the orthodox had to find reasons for the failure of air temperature to rise. The current orthodox explanation is that the warming has disappeared into the deep ocean. That has problems too. I would take the AGW scare more seriously if the human ‘signal’ were really distinguishable in the climate noise, and if it were significant.

5. That the evidence is clear-cut (= the science is settled). From what I have written above, it is clear, at least to me, that ‘the science’ of climate is simply equivocal about the AGW scare. Almost anyone can pick up a bundle of papers that support his or her position. I have done my best to look at both (all) sides of the issue, and have emerged as a ‘lukewarmer’ — that is, the earth is warming and will continue to warm, but slowly and without obvious threats either to humanity or the environment. I would become much less agnostic if there were more and more scientific papers that dealt with the issues I have raised above, and produced conclusions that showed the warming was unprecedented, caused by human activity, and dangerous — and these papers survived critical scrutiny.

6. That the computer models used correctly foretell  future climates. To the best of my knowledge, none of the GCMs that have been used by climate modellers has been both verified and validates, none has correctly predicted the passage of temperature change over the past twenty years, and virtually all their projections for the future seem way too high. In short, the models are running too hot, and one reason for that could be that they greatly over-rate the importance of carbon dioxide. I would begin to take serious notice of model outputs when it is agreed that one (or more) of the models have been properly validated and verified, and that they have correctly predicted what has happened. If it is in fact the case that climate is chaotic, and does not operate in a linear fashion, getting any model to that state would seem to me extraordinarily difficult.

7. That we need to change our way of life to deal with this threat. I would heed this injunction if I ceased to be agnostic.

Join the discussion 16 Comments

  • Mlcolm Miller says:

    Good summary, Don. Difficult to refute, but won’t convince any alarmists.

  • Peter Lang says:

    What would need to happen for me to agree that global warming has been caused by humans and is a real danger to humanity?

    Excellent question, Don. Of course, this is the question IPCC and the climate scientists should have been asking from the start. There should be a hypothesis with falsifiable predictions. The fact there are not shows that the CAGW hypothesis is not a scientific hypothesis.

    My quick response to the question is this:

    1. Define what evidence is needed to justify policies that will have costs to the budget. Treasury did the modelling analysis for the Australian carbon pricing scheme but relied on inputs and assumptions that have nowhere near the quality needed to justify the enormous expenditure these policies require ($1,345 billion net cost to 2050 according to Treasury estimates, but inevitably would be much higher net cost than that),

    2. Document the evidence that is required to support the case. The documentation needs to be of a standard needed for engineering quality assurance, for due diligence for the highest cost project ever undertaken, and for the most thorough adversarial interrogation (like Royal Commissions) ever undertaken.

    Examples of the quality of documentation required are the nuclear waste disposal programs such as Canada’s: http://www.nwmo.ca/home

    Steve McIntyre showed what is required to conduct due diligence. All the data, analysis procedures and models must be readily accessible, right down to the temperature records, tree rings, and drill core data so that any competent analyst can check the original data and reproduce the analyses and results. Scientists should spend far more time trying to falsify the results than trying to run models using unverified inputs.

    3. Lastly we need a thorough and rigorous adversarial process to test the information that leads to the policy analysis.

    The whole process of policy analysis, due diligence and adversarial interrogation should focus on the information that is key to the decision making, not the mass of mostly irrelevant scientific papers.

  • David says:


    Thanks for your interesting post.

    However, you have not explained what would make you change your mind. You have simply explained why you hold the beliefs that you do. What I am asking is, specifically what would evidence would you need to see to accept the AGW hypothesis.

    There is not right or wrong answer to this question. However, if we are open minded we should all think about this question from time to time. It would be equally as difficult for me to nominate a future threshold temperature, which would make me, reject AGW.

    • Lysander says:

      David – I am all for warming of 3-4 degrees upward. Bring it on. Depending on which scientific report you read; that means I have about 10,000 years to wait until this happens.
      Either way, it is better to build a sea wall than tax. It is better to build a desalination plant than tax. It is better to build sinks than tax (that’s the political argument rather than the scientific argument I subscribe to anyway)

    • Don Aitkin says:

      David, I did my best. What are you asking for? Give an example of the kind you think would satisfy you.

      • David says:

        Hi Don
        For example you could say if the 5-year average temperature in 2020 is above X degrees I will accept AGW.
        What value is X?
        Or in other words how hot does it need to get for you to change you mind?

        • Don Aitkin says:

          Right, understood. Your example doesn’t work because it doesn’t necessarily involve human attribution. I’ve already argued on other posts that we should prepare for climate changes however they are caused, by understanding their effects on us and trying to anticipate and deflect those effects. I can’t quite imagine what might cause an average temperature over five years by 2020 to be, say, above three degrees C higher than the five-year average from, say 2007 to 2012, but unless its cause was plainly human in origin, why would anyone accept AGW? How might its cause plainly be human (activity) in origin? We still can’t detect the human fingerprint or signal from the noise. (If you think that we can, please give me the links to the papers.)

          I can see what you are after. Perhaps you could think again and supply another example. I don’t think of the issue simply in terms of the arrival of a chunk of data that we all say ‘Aha!’ to. The AGW argument has several elements, as I set forward in the essay above. They’re all important, and they hang together. Though human attribution is important, no single piece of data will I think, show that it is real and most important. But I could be wrong.

    • Peter Donnan says:

      Your query about today’s posting is based on the title: there is an implication that Don might transition from agnosticism on climate change to one of acceptance if there was substantial evidence. Your point, David, about rising temperatures in your subsequent posting is a clear example of what might constitute such evidence.

      Many people tend to think about climate change in economic terms: will we be disadvantaged in a trading sense? Are incentives or punishment more likely to reduce carbon emissions? What about increased costs for electricity? Because Australia contributes such low emissions in a world-wide sense why should we be out of pocket? Economic, engineering and political perspectives tend to have higher priority than philosophical or ethical questions, or indeed those of many climate change scientists.

      For people to change their minds, it generally means that intellectual discussion, rationality, disputation of findings in the scientific literature etc are stampeded out the door by the sheer terror of events. If 10,000 people died from typhoons in Australia, America, and Britain simultaneously, and in the subsequent week there were catastrophic fires that unleashed hell, and then sea water rising became fearsome in many countries. It has to be almost biblical, apocalyptic or of terrifying science fiction proportion to change thinking. And then horrible vindictive crowds searching door to door for those false prophets who led them up the primrose path in such a balanced and intellectual manner.

      Clearly I am being a smartarse and I don’t think this is logical, nor is it likely to occur but perhaps these type of activities might be an answer to the question implied in the title.

      • Peter Lang says:

        Peter Donnan,

        You said:

        Economic, engineering and political perspectives tend to have higher priority than philosophical or ethical questions, or indeed those of many climate change scientists.

        But I’d argue that the ‘ethical’ arguments for carbon pricing are irrational and, in fact, immoral and unethical in the case of human caused climate change. They are irrational because the cost of policies like carbon pricing would be far greater than the benefit and have low probability of making any difference to the climate. So it is irrational to implement, promote or advocate such policies. Here I explain why they almost certainly would not succeed: http://jennifermarohasy.com/2013/08/why-the-ets-will-not-succeed-peter-lang/

        One of the problems seems to be that people try to attach and scarmongering and ewmotions to temperature change. But temperature change in itself is not bad. It is the consequences of the change that may be good or bad, perhaps, and we really have no idea at this stage whether any warming that does occur would be net good or net bad :


        Because Australia contributes such low emissions in a world-wide sense why should we be out of pocket?

        That’s not the argument. The argument is: why should we spend $12 for every $1 of projected benefit, especially given that it is highly unlikely that the ETS would deliver the projected benefits. Furthermore, the ETS would inevitably cost far more than the projections. On this basis it is irrational to proceed with policies that have very high costs and very low probability of delivering any benefits. According to Treasury estimates, the ETS would cost $1,345 billion to 2050. That’s about $50,000 per person. However it would inevitably cost much more and deliver probably no benefit. That is the reason people are opposed to the climate policies that have been proposed so far.

        Most people don’t know what the costs would be, but they have BS meters and they recognise when it doesn’t seem right and they can sense when they are being misled.

        • Peter Donnan says:

          Some brief thoughts on part of your posting, Peter:

          ‘ethical arguments for carbon pricing are irrational’: If you go back to first premises, you need to have a position on these questions: Is climate change happening at all? In what ways?

          What is happening in Australia at the moment is that there is a divide between those who remain unconvinced about the need to act on the implications of rising emissions and those who do. Protests yesterday around Australia – Greens, alarmists, emoters? – believe in the urgency of action and they see themselves as being informed by science and the signs of the times which may be subjectively interpreted. There is a coalition developing between community action and the ‘science’ around climate change and they may seek, like great movements of the past, to bypass political processes until it becomes undeniable. On the other side there are climate change deniers and agnostics who do not see the scientific evidence as compelling, who see a lop-sided cost benefit analysis.

          It is interesting you transition very quickly from ethics to financial costs. An ethicist might say if you believe deeply in values, and these are very high stakes values, then you act upon what you see as right, no matter the cost. It is a position of principle, of conviction, and is not comparative or dependent upon what others do. We don’t wait for moral guidance from the US or China because we are good moral citizens. We adopt a values-driven leadership position but this is clearly bizarre to those who remain unconvinced by the science and see it as grandstanding, a huge misallocation of resources etc.

          You have a very detailed and knowledgeable acquaintance with the costs and I could not dispute any point you make there. The only observation I would make is that you don’t include figures for the loss of lives, nor do you allocate figures on emotional devastation, life-long grief and a sense that there is an increasing intensity in weather events, no matter how subjective it is.

          This may be a classic case study between ‘reason’ and ’emotion’ but of course it is far more than that.

          The most telling point I have made in the small number of postings I have made is that I would be a lot more convinced by your arguments if you were a climate change scientist and led a team of 70 or 80 researchers around the world, closely involved in the figures around climate change – not the financial ones but those related to the physical phenomena we are considering. Does that preclude you and I from having different views or positions on the issues, or reviewing the data etc? Certainly not – that is the value of a site like this: a multiplicity of views are evident but their underpinnings are important.

  • Dave says:

    Thanks – especially for the link to ‘A Cool Look at Global Warming’. I suppose I liked it because it mirrors my views, but it was much more clearly and concisely stated than I have ever been able to manage. I remain unconvinced that CO2 is the primary driver of climate, see no good support for CAGW, and do not understand how a warmer, less variable global climate could produce increasing severe weather events. Of course, we just had the most extreme typhoon in the history of the universe, so I could be wrong.

    • Don Aitkin says:

      Dave, I think your last line is ironic, but indeed the last typhoon was not even the most powerful to hit the Phillipines, though it may have done the most damage.

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