2.2.1 Introduction

Earth system tipping points have the potential for major impacts on human societies by altering or magnifying the regional and global consequences of anthropogenic climate change (Figure 2.2.1). Regional and local impacts may occur as a result of passing tipping points such as permafrost thaw and forest dieback, some related directly to impacts on the land surface and others due to effects on regional climates and weather extremes. Global impacts may occur via large-scale alterations to atmospheric and ocean circulations, and also potentially by altering the rate and magnitude of global warming and/or sea level rise. 

Tipping points in the coupled ocean and/or atmosphere dynamics, such as shutdown of the Atlantic Meridional Overturning Circulation (AMOC), could have substantial influences on regional climates which are opposite to those expected without tipping – e.g. local cooling instead of warming. For tipping points that accelerate global warming and/or sea level rise, the impact relative to ‘non-tipping’ climate change projections would be to bring forward the timing of the hazard relative to levels of vulnerability, exposure and adaptation, potentially increasing the overall impact if there has been less time for societies to adapt. Passing tipping points in the cryosphere such as marine ice cliff collapse could lead to acceleration of sea level rise and/or commitment to greater long-term rise, both of which would affect the timing of increases in flooding hazards such as coastal inundation and storm surges. Biogeochemical tipping points such as Amazon forest die-back and permafrost thaw could potentially accelerate the increase in greenhouse gas concentrations in the atmosphere and hence accelerate global warming, leading to more rapid changes in the frequency or magnitude of extreme weather events, faster shifts in regional climates and more rapid sea level rise. 

So far, systematic assessments of the impacts of climate change on people and ecosystems presented in policy-relevant reports such as those of the Intergovernmental Panel on Climate Change (IPCC) and Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) have generally included little information on the implications for human societies of passing tipping points in the Earth system. This is also true of broader economic modelling of climate damages. While some national climate assessments, such as the UK’s third National Climate Change Risk Assessment (CCRA3) have included some consideration of the implications of tipping points (Hanlon et al., 2021), this has so far been limited in extent and often qualitative in nature. Quantification of the potential impacts of climate system tipping points is therefore widely recognised as a major knowledge gap.

This section will assess the current state of knowledge of the impacts and risks to people and ecosystems from specific Earth system tipping points, in comparison with projections that do not consider tipping points. Where possible, we draw on existing literature for this. Where literature does not yet exist, we use process understanding and expert judgement to assess how future projected impacts may change as a result of passing different tipping points.

We examine the potential impacts of Earth system tipping points from two perspectives (Table 2.2.1). First, we consider the impacts that may arise from a selection of individual Earth system tipping points, grouped into cryosphere, biosphere and ocean-atmosphere circulation tipping points. Second, we consider specific impact sectors and discuss how each could be affected by individual climate system tipping points and, where information is available, by combinations of tipping points.