Snow of Tomorrow | What are climatic tipping points?

The straw that breaks the camel's back

In the early days of the IPCC, climatic tipping points were still among the more eccentric, extreme visions of the future that were of little concern to the mainstream. This has since changed. Tipping points have long since entered the mainstream of climate science and are therefore gradually becoming part of public discourse. The IPCC defines tipping points as the points at which irreversible changes in the climate system occur.

From a more formal mathematical point of view, climatic tipping points are bifurcations combined with hysteresis in a dynamic system. We won't go into details, but hysteresis is an important concept to understand the principle of tipping points, so we will briefly discuss it: In simple terms, hysteresis refers to the dependence of a system state on its history.

Let's imagine a 32° steep, snowy slope. No avalanche has yet occurred on this slope (system state 1: slope intact). Now it is snowing half a meter. Whether the weight of the new snow will trigger a spontaneous avalanche depends on the snowpack structure, i.e. the previous history of the system. If the old snowpack is favorable, nothing may happen. However, if the situation is unfavorable, for example because the surface layer is weak, an avalanche will occur. The system state has thus changed abruptly and irreversibly (system state 2: slope has gone down)!

So, hysteresis: Depending on the previous history, small, gradual changes in a variable (e.g. fresh snow) cause small, easily predictable changes in the overall system (snow depth increases), or a fundamental change in the system state (avalanche goes down). When exactly the latter occurs is subject to some uncertainty with avalanches as with the climate - we know roughly how the whole thing works and when it starts to become critical, but at what moment exactly the system tips over (at how many centimetres of fresh snow does the weak layer break?) is not so easy to predict.

Why are tipping points so important

Why are we interested in when and where avalanches occur? When we cross a tipping point (avalanche starts), the uncertainty of future developments increases significantly. We don't know whether we will be buried or injured by the avalanche, what will happen to our ski touring buddies and what will happen next. As soon as we tumble down the mountain with the avalanche, our room for maneuver is also severely limited: If we're lucky, we can still react a little and pull the airbag, or try to bring our arms in front of our face for a breathing hole, but that's about it. When the avalanche comes to a halt, we have to somehow come to terms with the new situation, we can't simply return to the previous system state.

We understand risk as the combination of probability of occurrence and possible consequences, for avalanches just as for the climate. A total failure of AMOC is quite unlikely, but the global consequences would be dramatic. The comparison here is a little off, but we are also familiar with the "low probability-high consequences" problem from avalanche science. Other tipping points have higher probabilities of occurrence with perhaps less devastating, less direct consequences for humanity. Coral death due to rising water temperatures would be an example here - some coral reefs have already passed their tipping points. This changes the local ecosystem, but as inhabitants of the Alps we are not affected by this for the time being. Others - the melting of the large ice sheets - are more likely and also have major consequences (several meters of sea level rise), but these are not immediate.

Social tipping points

Climatic tipping points provide plenty of material for disaster movies, but falling into fatalism would be the wrong answer. There is still room for maneuver in many areas. We can still adapt our choice of route and decide not to climb up the avalanche slope. The idea that social change also has "tipping points", from which changes take place much faster and more radically, is increasingly finding its way into the climate tipping point discussion - not least to combat fatalism! One example is the falling cost of renewable energies, which will hopefully at some point result in politicians finally turning away from promoting fossil fuels, as they are simply becoming too expensive. The new technologies will gradually become better and cheaper (compare: more and more fresh snow is falling) until at some point it is no longer worth using anything else and the energy transition is complete (avalanche goes down/transition to a new system state).

A gradual change can eventually bring about systemic change and cause the proverbial barrel to overflow - for better or worse.