Rethinking climate tipping point risks

There’s no doubt about it: the concept of climate tipping points (CTPs) is just plain scary.  This refers to a series of critical Earth system thresholds which, if breached, could trigger irreversible and abrupt changes with far-reaching consequences for ecosystems, societies, and economies.

We’re talking doomsday-level stuff, here.  The most famous – and terrifying – CTP concerns the Atlantic Meridional Overturning Circulation (AMOC), a mega-current that traverses the globe, conveying warm water from the tropics to the northern reaches of Europe.  Data shows this current is slowing down as the word heats up.  One of the trendiest topics among climate scientists today is trying to estimate if and when the AOMC’s deceleration becomes “locked in” – in other words, when we’ll reach the point of no return   Losing the AOMC would upend all manner of Earth systems, likely plunging Europe into a deep freeze and sending global food systems haywire.

The AOMC tipping point has been in the spotlight (again) recently – both as the subject of a cover story in Wired magazine and of a paper in Science Advances, one with a controversial thesis.  This posits that there are simply too many uncertainties to predict when CTPs – like the AOMC collapse – will trigger, because the ways in which we extrapolate forward possible outcomes from historical data are not fit for purpose.

This claim ticked off Mark Trexler, a friend of Unpacking Climate Risk and creator of the incredibly useful Climate Change Toolbox.  His concerns centered on the implications for climate risk management:

Do climate risks go down because there is too much uncertainty for an accurate prediction? Does it change the fact that the risks of triggering tipping points goes up with a warming planet? I would argue that the answer to both questions is no, particularly given the potential existential nature of the risk. As Stefan Rahmstorf has pointed out, the risks of an AMOC collapse are such that we should act to ensure to 99.99% that it doesn't happen.

I think this touches on a key tension in the climate risk debate, and especially in the climate-related financial risk debate.  It’s the tension between ‘uncertainty’ and ‘risk’.  Risk is when the odds or probabilities of future events can be estimated.  Uncertainty involves unknown probabilities and unpredictable (and perhaps unknowable) outcomes.