2.1 Introduction

A separate glossary of the terms in bold is included as an appendix.

In Section 1 of this report, we examined the unsettling possibility of negative tipping points in the Earth system, where vital components that regulate the Earth’s climate, such as the cryosphere, biosphere, oceans and atmosphere, can abruptly shift. But the impacts of negative climate tipping points are not confined to isolated environmental disruptions: they have consequences for human societies. 

In Section 2, we shift the spotlight to these human impacts. We first unpack the impacts of the negative Earth system tipping points on human societies (Chapter 2.2), then explore how Earth system destabilisation could trigger ‘negative’ tipping points in human societies (Chapter 2.3). When these thresholds are met, they can trigger cascading effects across systems that might also impact the Earth system (Chapter 2.4). Finally, we give a summary of the potential to implement early warning systems for tipping points (Chapter 2.5). Governance to limit tipping points risks is dealt with in Section 3, while ‘positive’ societal tipping points, where societies transform to respond to the threats of climate and environmental change, are dealt with in Section 4.

The concepts of ‘negative social tipping points’ and ‘systemic risk’ are crucial to understanding this section. Negative tipping points are those that are predominantly harmful for humans and the natural systems we depend upon. Here, the word ‘negative’ is used in the value-based sense, not in the mathematical sense. Negative social tipping points, therefore, describe critical junctures within societies where small changes in biophysical drivers lead to ‘negative’ social, economic, or political change. For example, conflict tipping over into violence in the Lake Chad basin has likely partly been triggered by the shrinking lake. 

These tipping points can have different drivers. We limit our scope to negative social tipping points driven by change in the Earth system, while acknowledging that social drivers also contribute to enabling these tipping points. We acknowledge that ‘negative’ is a value judgement, as one person’s negative outcome may be another’s positive outcome, but in the most general sense, we consider a change to be negative when it is predominantly damaging for humans and the natural systems we depend upon. The repercussions of such tipping points extend far beyond their immediate contexts, impacting essential aspects of human wellbeing such as health (physical and mental), human security, and provisioning of other ecosystem services. 

As societies grapple with the dual challenges of Earth system and social tipping points, the concept of systemic risk has gained prominence (Juhola et al., 2022; Kemp et al., 2022; Centeno et al., 2015). This refers to a critical aspect of complex systems where the functioning of an entire system is compromised due to the interactions among its components (Sillmann et al., 2022). The idea is that the failure of one component can trigger a chain reaction of failures in other components, propagating the negative effects across the system, leading to widespread and often unforeseen consequences across the entire system. This can occur not only within a single system but also across different systems and sectors (e.g. ecosystems, health, infrastructure and the food sector) via the movements of people, goods, capital and information within and across boundaries (e.g. regions, countries and continents).

The main insights of each chapter are as follows. Chapter 2.2 assesses the impacts on people of the Earth system tipping points introduced in Section 1. These impacts have received relatively little, and uneven, assessment, with most existing assessments (such as the IPCC reports) focusing on the impacts of linear climate change. The chapter examines potential impacts of Earth system tipping points from two perspectives. First, it considers the impacts that may arise from a selection of Earth system tipping points. For example, tipping of ice sheets will amplify sea level rise, potentially exposing half a billion people to coastal flooding annually. Collapse of the AMOC would impact temperatures, precipitation and sea level worldwide. Permafrost thaw and Amazon dieback would affect water supply, built infrastructure, ecosystems and food supply in the affected areas, in addition to their global impacts via amplifying global warming through carbon release. Second, the chapter looks at  specific impact sectors, including water security, food security, energy security, health, ecosystems, communities and economies, and considers how each could be affected.

Chapter 2.3 demonstrates that climate change, potentially compounded by Earth system tipping points, could trigger negative social tipping points including eroded social cohesion, forced displacement, amplified polarisation, and security and financial destabilisation. These could also further accelerate climate change, including Earth system tipping, by undermining cooperation, resilience and response capacity.

Negative social tipping points herald the end of ‘business as usual’: human societies face a stark choice between an increasing risk of damaging, negative social tipping points or acting to accelerate positive change that mitigates Earth system tipping points and the risks they pose (Section 4). 

Just as Earth system tipping points could trigger each other like a series of dominoes (Section 1, Chapter 1.6), Chapter 2.4 shows that negative societal and ecological tipping points could themselves form cascades. This is a key source of systemic risk that could amplify the impacts of global changes, including Earth system tipping points, on humans. These tipping cascades are not unidirectional: disruptions in social systems can, in turn, alter how communities affect climatic and ecological changes (see Figure, 2.3.1). For example, conflict in the Lake Chad Basin has led to breakdown in governance of the region’s water resources and fisheries, leading to further degradation of those resources. This highlights how disruption in one domain can amplify disruption in others, underscoring the significance of these cross-sector interactions.

Amid the potential for negative social tipping points, the importance of early warning signals (EWS) emerges as an opportunity to enable proactive resilience. Anticipating the onset of tipping points, whether environmental or societal, may help decision makers avert or mitigate catastrophic outcomes. The concept of EWS for climate tipping points has been introduced in Section 1 (Chapter 1.5). Chapter 2.5 shows how similar methods can be used to anticipate negative social tipping points. However, the application of EWS methods to social-ecological systems differs from that to the physical Earth system due to their distinct characteristics and dynamics, presenting unique challenges. Specifically, human-influenced systems often involve a mix of social, economic and ecological components, making them inherently heterogeneous; human systems can exhibit abrupt changes on shorter timescales due to societal, economic or policy changes; and data availability in social-ecological systems can vary widely, with relevant data coming from mixed sources such as social media, economic reports, ecological surveys and remote sensing technologies.

To illustrate tipping point impacts, we give examples from different regions throughout Section 2. These examples highlight the diversity of tangible impacts on humans of tipping points in the coupled Earth-human system. We outline the impacts across systems and sectors. Our assessments are based on both empirical and modelling evidence. Together the evidence presented in this section provides strong motivation to swiftly act to minimise the risks associated with crossing Earth system destabilisation and tipping points including the negative impacts associated with them.

Further assessments of impacts of Earth system tipping points and negative social tipping points are urgently needed. Impacts of Earth system tipping points have received little attention in climate assessments and risks of negative social tipping points and their cascades have received almost no systematic analysis prior to this report. Our analysis of them is largely qualitative and case-based due to the limited available research. Given the catastrophic risks that negative Earth system and social tipping points pose for humans, substantial investment is needed to understand these risks, anticipate them with early warning signals, and govern them where possible.