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The best case for worst case scenarios

The “end of the world” or “good for you” are the two least likely among the spectrum of potential outcomes.

Stephen Schneider

Scientists have been looking at best, middling and worst case scenarios for anthropogenic climate change for decades. For instance, Stephen Schneider himself took a turn back in 2009. And others have postulated both far more rosy and far more catastrophic possibilities as well (with somewhat variable evidentiary bases).

This question came up last year in the wake of a high profile piece “The Uninhabitable Earth” by David Wallace-Wells in New York magazine. That article was widely read, and heavily discussed on social media – notably by David Roberts, Mike Mann and others, was the subjected to a Climate Feedback audit, a Salon Facebook live show with Kate Marvel and the author, and a Kavli conversation at NYU with Mike Mann this week as well. A book length version is imminent.

In a similar vein, Eric Holthaus wrote “Ice Apocalypse” about worst-case scenarios of Antarctic ice sheet change and the implications for sea level rise. Again, this received a lot of attention and some serious responses (notably one from Tamsin Edwards).

It came up again in discussions about the 4th National Assessment Report which (unsurprisingly) used both high and low end scenarios to bracket plausible trajectories for future climate.

However, I’m not specifically interested in discussing these articles or reports (many others have done so already), but rather why it always so difficult and controversial to write about the worst cases.

There are basically three (somewhat overlapping) reasons:

  1. The credibility problem: What are the plausible worst cases? And how can one tell?
  2. The reticence problem: Are scientists self-censoring to avoid talking about extremely unpleasant outcomes?
  3. The consequentialist problem: Do scientists avoid talking about the most alarming cases to motivate engagement?

These factors all intersect in much of the commentary related to this topic (and in many of the articles linked above), but it’s useful perhaps to tackle them independently.

1. Credibility

It should go without saying that imagination untethered from reality is not a good basis for discussing the future outside of science fiction novels. However, since the worst cases have not yet occurred, some amount of extrapolation, and yes, imagination, is needed to explore what “black swans” or “unknown unknowns” might lurk in our future. But it’s also the case that extrapolations from incorrect or inconsistent premises are less than useful. Unfortunately, this is often hard for even specialists to navigate, let alone journalists.

To be clear, “unknown unknowns” are real. A classic example in environmental science is the Antarctic polar ozone hole which was not predicted ahead of time (see my previous post on that history) and occurred as a result of chemistry that was theoretically known about but not considered salient and thus not implemented in predictions.

Possible candidates for “surprises in the greenhouse”, are shifts in ecosystem functioning because of the climate sensitivity of an under-appreciated key species (think pine bark beetles and the like), under-appreciated sensitivities in the West Antarctic Ice Sheet, or the North Atlantic overturning, and/or carbon feedbacks in the Arctic. Perhaps more important are the potential societal feedbacks to climate events – involving system collapses, refugee crises, health service outages etc. Strictly speaking these are “known unknowns” – we know that we don’t know enough about them. Some truly “unknown unknowns” may emerge as we get closer to Pliocene conditions of course…

But some things can be examined and ruled out. Imminent massive methane releases that are large enough to seriously affect global climate are not going to happen (there isn’t that much methane around, the Arctic was warmer than present both in the early Holocene and last interglacial and nothing similar has occurred). Neither will a massive oxygen depletion event in the ocean release clouds of hydrogen sulfide poisoning all life on land. Insta-freeze conditions driven by a collapse in the North Atlantic circulation (cf. “The Day After Tomorrow”) can be equally easily discounted.

Importantly, not every possibility that ever gets into a peer reviewed paper is equally plausible. Assessments do lag the literature by a few years, but generally (but not always) give much more robust summaries.

2. Reticence

The notion that scientists are so conservative that they hesitate to discuss dire outcomes that their science supports is quite prevalent in many treatments of worst case scenarios. It’s a useful idea, since it allows people to discount any scientists that gainsay a particularly exciting doomsday mechanism (see point #1), but is it actually true?

There have been two papers that really tried to make this point, one by Hansen (2007) (discussing the ‘scientific reticence’ among ice sheet modelers to admit to the possibility of rapid dynamic ice loss), and more recently Brysse et al (2013) who suggest that scientists might be ‘erring on the side of least drama’ (ESLD). Ironically, both papers couch their suggestions in the familiar caveats that they are nominally complaining about.

I am however unconvinced by this thesis. The examples put forward (including ice sheet responses and sea level rise, and a failed 1992 prediction of Arctic ozone depletion, etc) demonstrate biases towards quantitative over qualitative reasoning, and serve as a lesson in better caveating contingent predictions, but as evidence for ESLD they are weak tea.

There are plenty of scientists happy to make dramatic predictions (with varying levels of competence). Wadhams and Mislowski made dramatic predictions of imminent Arctic sea ice loss in the 2010s (based on nothing more than exponential extrapolation of a curve) with much misplaced confidence. Their critics (including me) were not ESLD when they pointed out the lack of physical basis in their claims. Similarly, claims by Keenlyside et al in 2008 of imminent global cooling were dramatic, but again, not strongly based in reality.  But these critiques were not made out of a fear of more drama. Indeed, we also made dramatic predictions about Arctic ozone loss in 2005 (but that was skillful). 

The recent interest in ice shelf calving as a mechanism of rapid ice loss (see Tamsin’s blog) was marked by a dramatic claim based on quantitative modelling, later tempered by better statistical analysis (not by a desire to minimise drama). 

Thus while this notion is quite resistant to being debunked (because of course the reticent scientists aren’t going to admit this!), I’m not convinced that there is any such pattern behind the (undoubted) missteps that have occurred in writing the IPCC reports and the like.

3. Consequentialism

The last point is similar in appearance to the previous, but has a very different basis. Recent social science research (for instance, as discussed by Mann and Hasool (also here)) suggests that fear-based messaging is not effective at building engagement for solving (or mitigating) long-term ‘chronic’ problems (indeed, it’s not clear that panic and/or fear are the best motivators for any constructive solutions to problems). Thus an argument has been made that, yes, scientists are downplaying worst case scenarios, but not because they have a personal or professional aversion to drama (point #2), but because they want to motivate the general public to become engaged in climate change solutions and they feel that this is only possible if there is hope of not only averting catastrophe but also of building a better world. 

Curiously, on this reading, the scientists could find themselves in a reverse double ethical bind – constrained to minimize the consequences of climate change in order to build support for the kind of actions that could avert them.

However, for this to be a real motivation, many things need to be true. It would have to widely accepted that downplaying seriously bad expected consequences would indeed be a greater motivation to action, despite the risk of losses of credibility should the ruse be rumbled. It would also need the communicators who are expressing hope (and/or courage) in the face of alarming findings to be cynically promoting feelings that they do not share. And of course, it would have to be the case that actually telling the truth would be demotivating. The evidence for any of this seems slim. 


To get to the worst cases, two things have to happen – we have to be incredibly stupid and incredibly unlucky. Dismissing plausible worst case scenarios adds to the likelihood of both. Conversely, dwelling on impossible catastrophes is a massive drain of mental energy and focus. But the fundamental question raised by the three points above is who should be listened to and trusted on these questions?

It seems clear to me that attempts to game the communication/action nexus either through deliberate scientific reticence or consequentialism are mostly pointless because none of us know with any certainty what the consequences of our science communication efforts will be. Does the shift in the Overton window from high profile boldness end up being more effective than technical focus on ‘achievable’ incremental progress or does the backlash shut down possibilities? Examples can be found for both cases. Do the millions of extra eyes that see a dramatic climate change story compensate for technical errors or idiosyncratic framings?  Can we get dramatic and widely read stories that don’t have either? These are genuinely difficult questions whose solutions lie far outside the expertise of any individual climate scientist or communicator.

My own view is that scientists generally try to do the right thing, sharing the truth as best they see it, and so, in the main are neither overly reticent nor are they playing a consequentialist game. But it is also clear that with a wickedly complex issue like climate it is easy to go beyond what you know personally to be true and stray into areas where you are less sure-footed. However, if people stick only to their narrow specialties, we are going to miss the issues that arise at their intersections.

Indeed, the true worst case scenario might be one where we don’t venture out from our safe harbors of knowledge to explore the more treacherous shores of uncertainty. As we do, we will need to be careful as well as bold as we map those shoals.


  1. S. Schneider, "The worst-case scenario", Nature, vol. 458, pp. 1104-1105, 2009.
  2. J.E. Hansen, "Scientific reticence and sea level rise", Environmental Research Letters, vol. 2, pp. 024002, 2007.
  3. K. Brysse, N. Oreskes, J. O’Reilly, and M. Oppenheimer, "Climate change prediction: Erring on the side of least drama?", Global Environmental Change, vol. 23, pp. 327-337, 2013.

130 Responses to “The best case for worst case scenarios”

  1. 101
    Karsten V. Johansen says:

    I forgot the link to the citations in my last part above. Here it is:

  2. 102
    zebra says:

    #99 Hank Roberts, #100 Karsten V Johansen, and others,

    So, as I often ask about other high-falutin’ suggestions…

    …what’s your plan?

    KVJ, your quote says it pretty well: “people and governments…still act as if it’s not happening”.

    So we get Hank’s guy, who uses “Deep”, the classic pseudo-profundity descriptor, because, you know, that’s going to change the minds of Putin and the Koch brothers and all, who are going to impoverish their country or themselves by not pushing FF on the world, by whatever means necessary.

    Yup, the problem is that Evil Globalist NeoLiberalism, and we can solve it by… Dictatorial Nationalism and Mercantilism. Except, that’s exactly what Putin and the Koch bros and all the others want, in order to keep selling their product.

    So, how about it? Can any of you suggest, in a realistic socioeconomic and geopolitical context, how best to avoid the worst case scenario?

    WCS, as I and others have said, would be an outcome of the interaction of the chaotic climate system with the chaotic human systems. Bad stuff is going to happen. What, other than a magical road-to-Damascus conversion of all the human actors (through endless puerile pontification by Deep thinkers), will minimize that?

    My best bet would be on Evil Globalist NeoLiberalism, actually.

  3. 103
    nigelj says:

    Yes global neoliberalism is preferable to nationalism and mercantalism, but some of neoliberalism’s ideas like rather open immigration ideas, and deregulated financial markets and privatised water supplies are barking mad. There has to be some sensible middle ground regulation of such things, or you have chaos and it will be essential with climate refugee problems, although hopefully “walls” can be avoided.

    Neoliberalism gets many of the basics right, but is also millimetres away from being a religion. You do realise this don’t you?

  4. 104

    If it weren’t for all the suffering and death, this would be a wonderful, interesting time.

  5. 105
    prokaryotes says:

    @Richard A Pauli I appreciate your comments since I first read them at ClimateProgress

  6. 106
    James Charles says:

    The ‘basis’ of neoliberalism?
    “This “equilibrium” graph (Figure 3) and the ideas behind it have been re-iterated so many times in the past half-century that many observes assume they represent one of the few firmly proven facts in economics. Not at all. There is no empirical evidence whatsoever that demand equals supply in any market and that, indeed, markets work in the way this story narrates.
    We know this by simply paying attention to the details of the narrative presented. The innocuous assumptions briefly mentioned at the outset are in fact necessary joint conditions in order for the result of equilibrium to be obtained. There are at least eight of these result-critical necessary assumptions: Firstly, all market participants have to have “perfect information”, aware of all existing information (thus not needing lecture rooms, books, television or the internet to gather information in a time-consuming manner; there are no lawyers, consultants or estate agents in the economy). Secondly, there are markets trading everything (and their grandmother). Thirdly, all markets are characterized by millions of small firms that compete fiercely so that there are no profits at all in the corporate sector (and certainly there are no oligopolies or monopolies; computer software is produced by so many firms, one hardly knows what operating system to choose…). Fourthly, prices change all the time, even during the course of each day, to reflect changed circumstances (no labels are to be found on the wares offered in supermarkets as a result, except in LCD-form). Fifthly, there are no transaction costs (it costs no petrol to drive to the supermarket, stock brokers charge no commission, estate agents work for free – actually, don’t exist, due to perfect information!). Sixthly, everyone has an infinite amount of time and lives infinitely long lives. Seventhly, market participants are solely interested in increasing their own material benefit and do not care for others (so there are no babies, human reproduction has stopped – since babies have all died of neglect; this is where the eternal life of the grown-ups helps). Eighthly, nobody can be influenced by others in any way (so trillion-dollar advertising industry does not exist, just like the legal services and estate agent industries).
    It is only in this theoretical dreamworld defined by this conflagration of wholly unrealistic assumptions that markets can be expected to clear, delivering equilibrium and rendering prices the important variable in the economy – including the price of money as the key variable in the macroeconomy. This is the origin of the idea that interest rates are the key variable driving the economy: it is the price of money that determines economic outcomes, since quantities fall into place.”

  7. 107
    Karsten V. Johansen says:

    Fascism of course is no alternative to liberal totalitarianism. It’s just an older form if the same: a more reactionary ideological fashion of the dictatorship of oligarchies.

    Neither will change the laws of nature. The only possible way to try to bring the GHG emissions down as fast as possible is to implement carbon fee and dividend: a fast rising and equally redistributed tax on all production of fossil hydrocarbons. Abandon all ideological symbolism and symbolic “politics”, break the deadlock created by media nonsense and its chattering classes and simply work for practical political solutions.

    Give up the “social” media nonsense. Act politically in democratic organizations like unions and grassroot movements.

  8. 108
  9. 109
    Hank Roberts says:

    So, with the decrease in solar activity, are we heading into another Maunder Minimum?

    “No Maunder Minimum. Certainly no Little Ice Age,” said David Hathaway, an astrophysicist who once headed NASA’s solar physics branch at the Marshall Space Flight Center. “The next cycle looks like it’s going to be very much like this one.”

    He explains that, while the sun does dim during a minimum, it’s only by a tenth of a per cent, which translates into a tenth of a degree Celsius. And with the warming by about 1C that we’ve seen due to climate change — and the warming that is to come — it’s unlikely that we’ll notice.

  10. 110
    Kent Peacock says:

    Thanks to those above who expressed interest in my paper, “A Different Kind of Rigor.” My apologies for posting a paywalled URL. Here is a link to a page with a free postprint of the paper, which corrects a few small misprints that appear in the journal version:

    I agree with post 100 above, by K.V. Johansen. Paleoclimate is a most valuable guide to what could happen, but we are taking the planet into new territory. What is going on now cannot be described as anything other than a planetary-scale emergency.

  11. 111
    nigelj says:

    “What is going on now cannot be described as anything other than a planetary-scale emergency.”

    Or death by 1000 cuts.

  12. 112
    SecularAnimist says:

    Paul Damascene wrote (#16):

    “One problem I find with the author’s thesis lies in his focus on worst cases around a single issue … one could contemplate a whole series of credible worst cases on a number of issues … a cascade of related and unrelated bad outcomes … that, overall, yield an outcome or outcomes worse than credibly expected or even imagined.”

    I strongly agree with this criticism of the “credibility” section of Gavin’s article. Gavin focuses on the credibility (or lack thereof) of a few individual potential “worst-case” phenomena, each of which would be, in and of itself, quickly and globally catastrophic.

    But the most plausible “worst-case” scenario is not some lurking “unknown unknown” time bomb that will wipe out life on Earth in a single stroke.

    The most plausible “worst-case” scenario is simply the combined, synergistic effect of all of the “well-known knowns” continuing to get worse, as they already are doing, and as they can be expected to continue doing in the absence of immediate action.

    That — rather than individually catastrophic “methane bomb” type scenarios — is what David Wallace-Wells is writing about in his article and book.

  13. 113

    JC 106: There is no empirical evidence whatsoever that demand equals supply in any market

    BPL: This reminds me of the frequent denier claim that “there is no empirical evidence whatsoever that carbon dioxide affects temperatures.” Just because you’re not aware of the evidence doesn’t mean there’s no evidence. To prove an enormous negative like the one you just advanced you would have to scour the economics journals to see that no one ever surveyed a market or calculated an elasticity. Good luck with that.

  14. 114
    James Charles says:

    Comprehension is not one of your strengths?

  15. 115

    #108-9, Hank–


    “The actual direct solar irradiance at the top of the atmosphere fluctuates by about 6.9% during a year (from 1.412 kW/m² in early January to 1.321 kW/m² in early July) due to the Earth’s varying distance from the Sun, and typically by much less than 0.1% from day to day.”

    I asked Tamino about a detectable temperature response over the annual cycle; his reply was that there is, but it is driven not by the change in irradiance but by the differential absorption between the Northern and Southern hemispheres, consequent to the unequal distribution of land and ocean.

  16. 116

    JC, I’m just fine on comprehension. Just because I disagree with you doesn’t mean I don’t understand what you’re saying. I understand just fine, I just think you’re wrong.

  17. 117
    zebra says:

    #107 Karsten VJ,

    It’s getting off topic, but it does serve as a nice illustration of why it is so hard to get things done.

    You say get away from politics, but you use the term “liberal totalitarianism”– and who knows what you think that means.

    And you want to “implement” fee and dividend… yes, another meaningless choice of language. Are you suggesting that such an “implementation” will occur through, as I said originally, a Road-to-Damascus conversion? An intervention by benevolent space angels/aliens, perhaps?

    No, it sounds to me like a job for a liberal elitist government, that can operate globally through the network of oligarchic financial interdependence, to influence/coerce other nation-state actors into compliance with the trade restrictions required.

    But that’s just silly me being hopefully pragmatic; it would be really difficult, but at least not just a vague fantastical arm-wave.

  18. 118

    JC 114: Comprehension is not one of your strengths?

    BPL: Economics is not one of yours.

  19. 119
    James Charles says:


  20. 120
    James Charles says:

    “Economics is not one of yours.”

    Since I was quoting a professor of economics this comment may be correct or incorrect and shows your complete lack of comprehension.

    As I say, comprehension is {definitely} not one of your strengths?

  21. 121
    nigelj says:

    James Charles @106. My understanding is demand does equal supply, most of the time anyway, yet your criticisms points 1-8 look mostly valid to me, but more related to the fact markets don’t operate optimally because of a range of human and system failings. I’m wondering if you or the person you quote are just confusing two separate issues.

    I read up on neoliberalism on wikipedia (for want of a better general overview) a few weeks back. The impression I get is a light handed version of neoliberalism makes some sense, but a heavy handed version goes seriously wrong. For example my country has benefited from some neoliberal ideas like free trade and reasonably fluid immigration and selling off some state owned companies and simplifying some onerous regulations, yet when we have pushed this into wider scale deregulation and privatisation we have started to experience problems. Its like there’s a sweet spot but going beyond this causes a cascade of quite serious failings.

    One thing free markets don’t self regulate adequately when it comes to matters of the environment, health and safety. History shows this conclusively, so governments, regulations, carbon taxes and courts become useful options. Any system or ideology that doesn’t recognise all this is not reality based.

  22. 122
    patrick says:

    Thank you for your excellent analysis. Thanks too for linking Margaret Klein Salamon’s informed article on “the recent seismic shift in the climate movement,” with many resources. I did not mind David Wallace-Wells’ original article (July ’17), because I like the concept of habitability and I was glad he introduced it. There are degrees of habitability, and it varies place to place. Failure is also by degrees and appears in some places more than others, and in stages, like a flood. As HJ (John) Schellnberger has said, death is often preceded by organ failure –it’s a process.

  23. 123
    patrick says:

    I misstated physicist and climate scientist HJ (John) Schellnhuber’s name (as “Schellnberger”) in my previous comment. Very sorry about that. There’s a great profile of Schellnhuber and his work in PNAS (2008):

    It touches on one (or more) of the subjects of this post.

    “I’m convinced that you simply have to provide the scientific evidence. If politicians ask ‘What is going on?’ they will turn to the best scientific institutions and not to those who are shouting the loudest. So it’s very important that you remain credible.” –Schellnhuber

  24. 124
    Alastair B. McDonald says:

    Patrick @123,
    You quoted:
    “I’m convinced that you simply have to provide the scientific evidence.” –Schellnhuber

    Can’t you see that, while that may seem honest and reasonable, scientists have been doing that for thirty or more years now, and it has not worked!

    The sceptics and deniers have been using every trick in the book to get their message across, and they have prevented any meaningful contraction of fossil fuel burning from taking place. Atmospheric CO2 CONTINUES TO RISE.

  25. 125
    Radge Havers says:


    “I’m convinced that you simply have to provide the scientific evidence. If politicians ask ‘What is going on?’ they will turn to the best scientific institutions…”

    Heh: Don’t y’all get uppity, hear!

    Set aside for the moment that scientists do indeed need to be cool and maintain their professional demeanor. Let’s consider the state of congress and, just for fun, check out the two videos on this thread at Pharyngula:

    How will it all end? We don’t know, but I’d suggest supporting the adults in the room–when by some odd chance you manage to find them.

  26. 126
    Hank Roberts says:

    Hat tip to Metafilter;

    The sea level in Miami has risen ten inches since 1900; in the 2000 years prior, it did not really change. The consensus among informed observers is that the sea will rise in Miami Beach somewhere between 13 and 34 inches by 2050. By 2100, it is extremely likely to be closer to six feet, which means, unless you own a yacht and a helicopter, sayonara. Sunset Harbour is expected to fare slightly worse, and to do so more quickly.

    Thus, I felt the Sunset Harbour area was a good place to start pretending to buy a home here. Amazingly, in the face of these incontrovertible facts about the climate the business of luxury real estate is chugging along just fine, and I wanted to see the cognitive dissonance up close….

  27. 127
    Hank Roberts says:

    “The scientists, economists, and environmentalists that are saying this stuff, they don’t realize what a wealthy area this is.” She said that she lived here and wasn’t leaving, and that the people selling Miami were confident, and all working on the same goal as a community to maintain this place, with the pumps and the zoning and raising the streets. There were just too many millionaires and billionaires here for a disaster on a great scale to be allowed to take place.

    “Anyway, people are working really hard to prevent anything from happening,” she continued.

  28. 128


    Thanks, Hank. That piece is a good an examination of the psychology as anything I’ve seen lately.

    I can laugh at the prettily arranged soap, or the privately-viewed sunsets, or the Jet Skis, because those are not my drugs, but Niu Kitchen, and all that goes with it, will be dragged from my fake wedding-ring-adorned cold dead hands.

    And you know, this might actually happen! How do we think this is all going to end? With the election of a better candidate? With the passing of a law?

    Full disclosure: I live in a town in rural Northern California that could burn down to the ground literally any day, and I’m thinking about buying a house here.

    Of course, personally, I am an optimist. I think we’ll see better laws passed, and better candidates elected. I expect to see the decarbonization of the grid and the electrification of transport continue, and in fact accelerate. I’m quite confident that there are a great many folks who today are spouting denialist claptrap (or maybe the real-estate-ese platitudes the popula story quotes) with wise expressions, who in twenty or ten or five years will have retrospectively recast themselves as climate change versions of the prophet Isaiah (or maybe Jeremiah) because, well, ‘everybody knows,’ and of course they knew early.

    But the Golden Age will not thereby be established. We’ll still be in an existential struggle, still trying to figure out what society ought to look like given a rapidly changing reality, still trying to decide which pieces of the past need to be held onto, and which need to be tossed yesterday. We’ll still be fighting, literally and metaphorically, over how to live.

    In short, it’ll still be a mess–but, optimistically, a mess at a slightly higher level.

  29. 129
    Thomas Marvell says:

    The worse case is now getting to be the new normal: equilibrium climate sensitivity 5°C+.

  30. 130
    Justin Bowles says:

    On Tail Risks

    I really wanted to attach this to Gavin’s “The best case for worst case scenarios” but comments appear closed there.

    I’ve just read William Nordhaus’ 2018 paper “Projections and Uncertainties about Climate Change in an Era of Minimal Climate Policies” in the top-ranked American Economic Journal. Nordhaus is the doyen of climate change economists with a 2018 Nobel Prize to boot for his efforts.

    The paper has some interesting figures on worst-case scenarios that just don’t appear to be found in the physical climate science literature. Here is the paper.

    Please look at the box plots in Figure 7A on page 354 for the journal. The top two cover the principal variables out of the climate science: CO2 concentrations and temperature rise.

    The temperature change box plot appears shocking to me. For 2100 on his business as usual CO2 emission scenario, Nobel laureate Nordhaus has the median temperature rise at 4 degrees of warming and the top of the interquartile range at 5 degrees. Further, the whiskers are extending up to 7 degrees.

    I guess I have two questions. Based on Nordhaus business as usual CO2 emission projects, are those box plots wrong? In particular, is his top of the interquartile range warming of 5 degrees warming wrong? That doesn’t look to me like a black swan tail risk at all, but the implications for the planet are horrendous.

    Finally, this box plot approach to showing risk outcomes is pretty much Statistics 101. So why am I seeing this here in a paper by an economist on climate change and not in an IPCC report? If ever there was a call to arms for climate change mitigation then surely Nordhaus’ box plot is it. Far more powerful than anything in the IPCC reports.

    In economics, finance, insurance and so on we are obsessed with the tail risks. Yet the majority of climate change communication is at the 33%, 50% and 66% confidence levels. No drug trial would operate at these levels. What is going on at the 5% level and why is it not being communicated?