Climate change risks

I thought I would briefly mention a paper, by Simon Sharpe, that is currently under review and that discusses how we should present climate risks. It was highlighted by Steve Forden on Twitter and suggests that climate risks should be plotted as probability over time. The suggestion is that what we mostly see are impacts (such as global surface temperature) plotted against time. The paper argues that

a more appropriate means of assessing and communicating the risks of climate change would be to produce assessments of the likelihood of crossing non-arbitrary thresholds of impact, as a function of time

Credit: Schellnhuber et al. (2016)

The ideas, as I understand it, is to consider some thresholds beyond which we might expect some impacts to materialise. We can then present the probability of us crossing these thresholds and how this probability will change with time under various scenarios.

For example, as the figure on the right illustrates, if we cross 2oC we have a high chance of losing coral reefs, and a reasonable chance of losing Apline glaciers and summer Arctic sea ice. If we warm further, then other outcomes become possible, and become increasing likely if we continue to warm. If we could quantify the probability of these various outcomes, and how this changes with time, then we could inform what we would need to do if we wanted a good chance of avoiding some, or all, of these outcomes. Similarly, we could highlight at what point some of these outcomes become very likely if we do not take action to avoid them materialising.

Although I do think it is useful to consider things in this way, I can see some complications. The probability of various outcomes depends largely on the emission pathway we actually follow. Although we have some control over future emission pathways, it’s not straightforward to determine the actual probability of actually following one. Hence, it’s not clear how we can really quantify the likelihood of crossing non-arbitrary thresholds.

We could, of course, present conditional probabilities (i.e., how the probability of crossing some threshold varies with time given some emission pathway) but this suggests that this framing isn’t quite as straightforward as it may seem. I do still think, though, that this is a reasonable way to consider this. It may be that there is some straightforward way to present this, but I suspect that this is a topic about which nothing is ever quite straightforward.

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10 Responses to Climate change risks

  1. John Hartz says:

    ATTP: By happenstance, I came across the following article today. What it describes and illustrates in graphic form is another dimension of what you have addressed in your OP.

    Visualizing Interconnections Among Climate Risks, Mindzilla, Feb 28, 2019

  2. Further to your point that it is unclear that “time” is what we should be measuring ‘probability of impact” against… I am not even sure that we should be measuring it against “emission pathway” as against “cumulative emissions” (*). Which, you could further then turn back into time by saying that you will cross threshold X of cumulative emissions (and probability Y of impact Z) within W years on the current emission pathway.

    Which is pretty hard keeping track of, but I think you need cumulative emissions or a carbon budget in there. (* and, of course negative emissions has made the whole carbon budget framework far more problematic, but presumably you still hit a peak in the cumulative carbon emissions…)

    By the way, the risk/impact I would be most concerned would be the one(s) described last year in “Trajectories of the Earth System in the Anthropocene”/, which – as you would know – considers the disturbing possibility that there is no stable climate around 2C… That there may be attractors in Earth system dynamics that initiate and reinforce warming and carbon feedbacks so that the system moves to discrete stability points far outside the Holocene of Holecene ~+2C,,, That, to me, is a risk/impact that we should be communicating and working to avoid above all others…

    Trying to make that a bit more lucid: I am more concerned about a (the) cascade of reinforcing impacts than I am in considering them one by one…

  3. Everett F Sargent says:

    Stuff like this …

    “or the height of sea level at which it becomes less costly to relocate a coastal city than to continue to protect it against flooding”

    “the impact of a past event whose damage is well understood, e.g. a storm surge equal to that of
    Superstorm Sandy”

    There are places where this is completely covered from a risk standpoint and they ain’t in the UK!

    We all got more than our fair share of sand dunes and barrier islands and tropical and extratropical storms. Not even sad, just plain pathetic. :/

  4. KiwiGriff. says:

    For example, as the figure on the right illustrates, if we cross 2oC we have a high chance of losing coral reefs, and a reasonable chance of losing Apline glaciers and summer Arctic sea ice.

    Yes it all sounds so unthreatening.

    Coral reef ecology is part of the life cycle of many commercial fish species that we will lose. We also lose the coastline protection and land building generated by coral reefs over time.
    Alpine glaciers supply consistent running water that irrigates land over large areas so we may lose agricultural productivity and water security over huge regions. Summer sea ice has a significant effect on global weather as we see with the meandering jet stream “Polar vortex” weather pattern that seems to be emerging.

    We are talking about simultaneous effects that dont just add they multiple the risk of significant impacts.

    Lose 10% of fisheries due to coral die off another 10 % from loss of productivity due to losing the moderating effects on stream flows from glacial melt and 10% from inconsistent seasonal weather patterns effecting agriculture and you are looking at the possibility of 30% of global food supply lost. Even if such effects coincide only once every few years …. when it does Global catastrophic food crisis’s resulting in wars and famine .

    We are loading the dice far in excess of the individual risks taken in isolation .

  5. Kiwi,
    Sure, I wasn’t suggesting that there aren’t even more severe impacts that we should be highlighting. I also agree that the issue of multiple impacts coinciding is something to consider.

  6. Steven Mosher says:

    Even though I like this chart ATTP, I’d like to see a follow up.

    A storyline for every one of those tipping point stand pipes. so 5 stories and all the related
    impacts over time.

    I’d wager within those tippiong point stories lines you’d have one that was closest in time, that was highest probability and most impactful ( connected to other things)

    As for scenarios, for rhetorical effect, I’d do a projection where every country started to follow the percentage of cuts in emissions that the UK has. Just to put it in a framework of what is proven to be achievable.. we have abstract scenarios ( 2.6, 8.5 etc) but it would be a good rhetorical effect to say ‘Assume every nation cut there emissions as the UK has over the last x years)

  7. Steven,
    Yes, that all sounds quite reasonable. You would then run into the standard problem of it becoming rather complicated and it being more difficult to present something that could have some kind of impact on those who don’t have the time, or inclination, to delve into all of the details. Some of what you describe already exists in things like the IPCC reports.

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  9. John Hartz says:

    Speaking of risks…

    A Nearly $1 Trillion California Flood Likely to Occur Within 40 Years by Jeff Masters, Category 6, Weather Underground, Mar 4, 2019

    The $1 Trillion Storm: How a Single Hurricane Could Rupture the World Economy by Geoff Dembicki, Vice, Mar 3, 2019

  10. Steven Mosher says:

    Ya ATTP.

    My sense is such a presentation would not be for everyone.
    but once you have the complete storyline its easy for story tellers to shorten the plot,
    pick the main characters, and still hew to the truth

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