Climate change as a matter of risk management requires different choices in communication


Rowan Sutton just published a very short article (an “idea”) in ESDD entitled “a simple proposal to improve the contribution of IPCC WG1 to the assessment and communication of climate change risks”. From a risk management point of view a focus solely on the most likely outcome is not recommended, especially when the impacts increase sharply towards one end of the scale.


A common measure of risk is likelihood x impact (Fig 1). It is standard practice in risk assessment to highlight both the most likely impacts and low likelihood high impact scenarios. Such scenarios merit specific attention because the associated costs can be extremely high, so decision makers need to know about them. It follows that WGI has a responsibility to assess and communicate explicitly the scientific evidence concerning potential high impact scenarios, even when the likelihood of occurrence is assessed to be small. In past reports the assessment of key parameters by WG1 has focussed overwhelmingly on likely ranges only. When information has been provided about the tails of distributions only likelihoods have been communicated using terms – following the IPCC’s uncertainty guidance (Mastrandrea et al, 2010) – such as “very unlikely” or “extremely unlikely”: a clear steer that policy makers should largely ignore such possibilities. But this is wrong. Policy makers care about risk not likelihood alone. The IPCC’s uncertainty guidance ignores impact and is symmetric with respect to high or low impact scenarios; this is inappropriate for the communication of risk (Fig 1).

Figure 1: A schematic representation of how climate change risk depends on equilibrium climate sensitivity (ECS).

Some will argue that the WGII report is needed to provide information on impacts. For detailed information this is certainly the case, but the general shape of the damage function for a large basket of impacts (Fig 1) is insensitive to such details, and is all that is needed to justify WGI providing a much more thorough assessment of relevant scenarios. Other critics will suggest that for WGI to identify high impact scenarios explicitly would constitute scaremongering; this concern is no doubt one reason why previous WGI reports have focused so much on the likely range. But it is misguided. Policy makers need to know about high impact scenarios and WGI has a responsibility to contribute its considerable expertise to making the appropriate assessments.

A very similar point has been made by Kerry Emanuel in his post “Tail risk vs Alarmism” on CCNF:

In assessing the event risk component of climate change, we have, I would argue, a strong professional obligation to estimate and portray the entire probability distribution to the best of our ability. This means talking not just about the most probable middle of the distribution, but also the lower probability high-end risk tail, because the outcome function is very high there.


But there are strong cultural biases running against any discussion of this kind of tail risk, at least in the realm of climate science. The legitimate fear that the public will interpret any discussion whatsoever of tail risk as a deliberate attempt to scare people into action, or to achieve some other ulterior or nefarious goal, is enough to make almost all scientists shy away from any talk of tail risk and stick to the safe high ground of the middle of the probability distribution. The accusation of “alarmism” is quite effective in making scientists skittish in conveying tail risk, and talking about the tail of the distribution is a sure recipe to be so labelled.

Hans Custers schreef een kort Nederlandstalig blog over Sutton’s artikel.


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7 Responses to “Climate change as a matter of risk management requires different choices in communication”

  1. Thomas Fuller Says:

    Sigh… paging Nicholas Taleb. Nicholas Taleb, white courtesy phone.

  2. Thomas Fuller Says:

    Bart, could you please list the high impact, low probability events associated with climate change?

    Would you also please indicate the metric (GST, SLR, whatever) that will bring those risks to reality?


    Event: Rendering of large amounts of coastal land uninhabitable due to SLR, storm surge, other…

    Metric: 1.5 meters of SLR

    Probability: X%.


    You don’t need to provide an exhaustive list.



  3. gcitytimes Says:

    What ARE the most effective means to find sustainable solutions to a temperature rise of 4-6° Celsius (by the end of the century) that will result in catastrophic climate change if the status quo path of fossil fuel consumption is not curtailed by sustainable solutions? I posit the most effective arguments are not debating the merit or minutiae related to the scientific consensus on global warming as detailed in the IPCCC report, but instead economic arguments as;
    1. the LCOE of renewable energy is now generally less expensive than that of fossil fuels
    and 2. conservatives will generally respond better to economic arguments

    With that in mind, Green City Times has developed set of actionable goals in order to stabilize greenhouse gas emissions on a global scale>>>

    Please let me know your thoughts.

  4. Jeff Id Says:

    Communication is not the problem. Lack of evidence and broken models are. And for those of us who understand models and evidence, complete lack of recognition by those claiming to be experts of that original and very key lack.

    Add in the insanity of the ‘expert solutions’ and you can communicate until you are blue and nobody’s buyin.

  5. Dirk Roorda Says:

    Maybe the existence of high impact risks can be established without giving a list of them and without stating their probabilities.

    There are several positive feedback loops in the climate system. Probably there are a few surprises. A larger amount of methane escapes than expected by 2050.

    If such a feedback loop kicks in, we could see an increased sea level rise during a short time.

    So, if you tweak a parameter (CO2) in a system like this for more than one century into the same direction, there is a certain chance that you get a catastrophic outcome within that century.

    But we do not know enough about the state space of the whole system to compute the probability that we end up in a certain corner of that space.

  6. kurma514 Says:

    I think the most important in this decade is how we make the earth as our friend by planting trees as much as we can. I found that date palm tree is very adaptable in every continwntal and every type of land. We’re in Indonesia already propagate thousands and plant date palm trees, we hope in the future our economic growth (positive) while we refresh the planet and climate change mitigation.
    Let’s support each other to make our earth GREEN and cool for our next generations.
    Arie Prasetya

  7. Aurélio Barbato Says:

    Reblogged this on Obras e Serviços Guaiaó Influence Marketing Platform 260 Stars Engenho Talento e Arte and commented:

    Zeke Hausfather
    Criticizing action on climate change that falls short of reforming capitalism is a great way to get nothing done while global emissions continue to increase.

    Don’t let the perfect be the enemy of good clean energy technologies that are actually making a dent in CO2 today.

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