2.4.5.1 Clarification of concepts

Most of the current research has focused on understanding the tipping processes in different natural systems. Recent research on cascades has illustrated the role that they have in the emergence of different types of risks (Sillmann et al., 2022; Simpson et al., 2021). However, the role that cascades can play in tipping is less well understood, especially when they involve a combination of social and Earth system tipping points.. This section of the report identifies the following concerns that ought to be addressed in future research. 

When identifying tipping cascades, it is necessary to identify clear boundaries of which systems are involved. This also involves establishing what are the system states and dynamics in order to identify how the tipping cascades alters them (i.e. a change in the reference condition of the system). For example, identifying differences between system states can be unclear, such as ‘fragmented’ vs ‘non-fragmented’ landscapes, or ‘forested’ vs ‘deforested’, which are continuums with easily recognisable end points but a hazy centre. This is particularly challenging in a social system, where identification of system state, dynamics and drivers of change is nascent and where observations over time are scarce. 

It is also necessary to clarify whether cascades are identified within or across system boundaries.  Furthermore, there are ambiguities regarding whether there is a threshold when a cascade emerges or stops and whether these can be identified. 

It is also necessary to clarify the type of relationships between tipping cascades that relate to causality. For example, does the occurrence of a tipping point in a system (A) increase the likelihood of another system (B) tipping? Systems A and B may be far away in space and have different temporal scales. For example, non-linear relationships between phosphorus levels in shallow lakes and the growth rates of phytoplankton mean that, under certain conditions, small additions of phosphorus can lead to algal blooms and a rapid, hard-to-reverse deterioration in water quality (Scheffer, 2020; Scheffer et al., 1993; Carpenter et al., 1999). Declining water quality can cause a similarly non-linear or disproportionate response in the social and economic components of the freshwater social-ecological systems, for example through a rapid reduction in tourism revenue or property prices around a lake. Since management responses to removing phosphorus from the system, for example by  limiting runoff from dairy farms upstream, are often slow to become effective, the initial ecological tipping point can trigger cascading effects through the broader social-ecological system (Schindler et al., 2016).