Module 4: Risk Under Deep Uncertainty
Climate surprises: Tipping points
Another possibility that throws a wrench into probabilistic modeling is the risk of an abrupt change in the climate system itself—a change either in the equilibrium state of the system or in its system dynamics. Such a change implies a corresponding sudden shift in the probability distribution for events that are produced by the system (like extreme weather).
Many of our adaptation planning models and our financial impact forecasts are based on an assumption that the climate will change gradually—perhaps gradually enough for us to adapt or alter our socioeconomic response to it. However, there are good reasons to question that assumption. For example, the paleoclimate record includes many such examples of abrupt changes in ocean and air circulation, and extreme extinction events (National Research Council, 2013).
These abrupt changes are generally seen as the consequences of crossing some threshold or “tipping point” beyond which changing system dynamics draw the system toward a new equilibrium. Common examples of tipping points in climate systems include loss of Arctic sea ice, which diminishes ice albedo, leading to increased temperatures, faster sea ice lost, and further diminished albedo. Or permafrost thaw that results in the release of methane into the atmosphere, increasing the atmospheric stock of greenhouse gasses, accelerating global warming and further permafrost thaw. Note that both these examples involve feedback loops in the climate system that result in an amplification of the initial disturbance.
For a list and description of some important climate tipping points, see McSweeney, R. (2020). Explainer: Nine ‘tipping points’ that could be triggered by climate change. Carbon Brief.
Some climate scientists suggest that some climate tipping points have already been activated, and that we are dangerously close to activating others. The authors of one such study conclude, “If damaging tipping cascades can occur and a global tipping point cannot be ruled out, then this is an existential threat to civilization. No amount of economic cost–benefit analysis is going to help us. We need to change our approach to the climate problem” (Lenton, T.M., et. al. (2019). Climate tipping points—too risky to bet against. Nature.) Notice the similarity of Lenton’s conclusion to Weitzman’s conclusion regarding fat-tailed distributions.
Tipping points are also possible in socioeconomic system as well, including technology and adaptation systems. For a brief overview of some of these tipping points, read van Ginkel et al, Climate change induced socio-economic tipping points: Review and stakeholder consultation for policy relevant research Section 3 (pp. 3 – 7) only.