2.4.1 Introduction

We review the role and prevalence of cascading impacts in relation to tipping points. We focus on identifying cascading impacts across biogeophysical and social systems in order to illustrate how a cascade from a tipping point in one system can lead to an increasing likelihood of breaching a tipping point in another. We do this by focusing on the interactions between natural and social systems across different temporal and spatial scales. The outcomes of these tipping cascades can be negative or positive, depending on the systems involved, actors in those systems and over different periods of time.    

The literature is clear that there are interactions and feedbacks between systems that affect each other and can lead to abrupt changes (Liu et al., 2023; Wunderling et al., 2023). These are often termed as cascading impacts, which can be defined as “a sequence of events where abrupt changes in one component lead to abrupt changes in other components. These changes could also interact with each other and propagate from larger to smaller spatial scales or vice versa” (Brovkin et al., 2021).  

Cascade as a term has multiple meanings, generally describing the sequential occurrence of similar events. e.g. A is followed by B, which is followed by C (Klose et al., 2021). Cascade as a term has also become commonly used in assessing climate risks (Simpson et al., 2021), implying that risks are passed on from one stage to another. Cascading risk, for example, has been defined as one event or trend triggering others and these interactions can be one-way (e.g. domino or contagion effects) but can also have feedbacks (Helbing, 2013). Klose et al., (2021) propose an ideal model of three different types of cascades: 1) two-phase cascade, 2) domino cascade, 3) joint cascade. However, it is not clear to what extent this can be extended to the study of cascades between biogeophysical and social systems.

Cascade as a term is increasingly used to characterise systemic risk (i.e. a risk that a failure of one element will lead to system-wide adverse impacts or an entire system collapse). According to Sillmann et al., (2022), systemic risk is exemplified by cascades that spread within and across systems and sectors (such as ecosystems, health, infrastructure or the food sector) via the movements of people, goods, capital and information within and across boundaries (for example, regions, countries or continents). The spread of these impacts can lead to potentially existential consequences and system collapse across a range of time horizons (Sillmann et al., 2022). 

So far, there has been increasing interest in cascading impacts of tipping points (Brovkin et al., 2021) but less conceptual development or empirical work of the processes constituting such cascades. Many of the contributions highlight the nature and the importance of the problem (Franzke et al., 2022), but there is a shortage of empirical knowledge or clear conceptual understanding of the role that cascades play in facilitating or hindering tipping points between systems. 

We interpret cascades here to refer to a tipping cascade, which occurs when passing one tipping point triggers at least one other tipping point. Here, this means ecological tipping points can lead to cascading impacts that trigger social tipping points, and vice versa. It is useful to point out that a cascade effect in current literature is considered a causal change where a change in one system can trigger a further change in another system. In these instances, tipping can be driven by such cascades but not necessarily. 

The aim of this chapter is to advance the state-of-the-art understanding of cascades across scales and systems between Earth system and social tipping points. We argue that this understanding is constrained by lack of conceptual clarity and empirical evidence. In order to address this gap, we review the current state of literature on cascading tipping events and identify where most of the evidence base is. We also use five case examples to identify emerging research questions regarding what temporal and spatial scales, and associated dynamics and sequences, are relevant to study tipping cascades.