Status quo

Scientific knowledge about ESTPs has expanded significantly over the last 20 years, with most of this research conducted within the natural sciences. This report’s scope provides a broader lens than previous work, including additional Earth system tipping elements (Table 1.7.1 & Figure 1.7.1). While modelling efforts are expanding, many Earth system and climate economy models today still lack representations of tipping dynamics, especially couplings between social and biophysical processes (Franzke et al., 2022). At the same time, despite the research summarised in Section 2, there is a significant knowledge gap regarding the social and human dimensions of Earth system tipping, from expected impacts, risks and vulnerabilities to implications for decision making and governance, including framing effects, actor motivations and the role of political power.

Given that this solutions-oriented knowledge is essential to support the development of a governance and policy agenda on ESTPs, its scarcity is a reason for concern.

The IPCC has addressed climate tipping points since its third assessment report (AR) with varying terminology (see Box 3.4.1). The topic received growing attention in more recent assessment cycles, but has not yet led to active engagement among international or national policymakers, with tipping points not yet part of the UNFCCC negotiation agenda (Milkoreit, 2015; 2019).


Tipping points and the Intergovernmental Panel on Climate Change

The IPCC first addressed climate tipping points in its 3rd Assessment Report (McCarthy et al., 2001), using the terminology of ‘large-scale discontinuities’ in the report of Working Group II (Impacts, Adaptation and Vulnerability). Tipping points were included in a set of ‘reasons for concern’, visualised in the ‘burning embers’ diagram that later motivated the selection of the 2°C temperature goal (Leemans and Vellinga, 2017). At this time, the IPCC concluded that tipping points would only become likely if global average temperatures exceeded 4°C. 

The burning embers were not included in AR4 (IPC, 2007), but scientists independently published an updated figure in 2009 (Smith et al., 2009). It returned in the AR5 WGII Summary for Policymakers (Field et al., 2014), which referred to ‘large-scale singular events’ as a reason for concern, or RFC. AR5 Working Group I defined tipping points as Earth system components that are ‘susceptible to abrupt or irreversible change’, focusing on irreversibility and the likelihood of the occurrence of tipping points in the 21st Century (Collins et al., 2013). More than a decade after AR3, the IPCC updated its risk assessment for the transgression of tipping points, stating that they “become moderate between 0-1°C additional warming [above 1984-2005 average], […]. Risks increase disproportionately as temperature increases between 1-2°C additional warming and become high above 3°C, due to the potential for a large and irreversible sea level rise from ice sheet loss” (Field et al., 2014; Assessment Box SPM.1). AR5 also contained a table listing nine Earth system components that are “susceptible to abrupt or irreversible change” (IPCC AR5 WG, 2014 I, Table 12.4, p.1115). These included AMOC, ice sheets, and tropical and boreal forest dieback. Lenton et al., (2019) showed how the IPCC’s risk assessment of tipping points had changed over time (Figure 3.4.1).

Figure: 3.4.1
Figure 3.4.1: Changing risk assessment of tipping points in IPCC reports over time. The IPCC has assessed the risk of tipping points (‘large-scale singular events’) as one of five ‘reasons for concern’ in a bar graph (‘burning embers’) to motivate climate action in most of its assessment reports since 2001. Colours indicate levels of risk from white (undetectable) to yellow (low), red (high) and purple (very high). Each AR increased the level of risk expected for a specific level of warming. 

IPCC, 2023) updated the burning embers diagram (IPCC 2023), maintaining the language of ‘large-scale singular events’ (IPCC 2023). The IPCC’s WG I defined a tipping point as “a critical threshold beyond which a system reorganises, often abruptly and/or irreversibly”. It also used the related term abrupt climate change, defined as “a large-scale abrupt change in the climate system that takes place over a few decades or less, persists (or is anticipated to persist) for at least a few decades and causes substantial impacts in human and/or natural systems”. (IPCC 2023). AR6 WGI sometimes uses ‘tipping point’ to refer to a class of abrupt change in which the subsequent rate of change is independent of the forcing [IPCC 2023). AR6 assessed the risk of tipping point transgression as moderate today (at more than 1ºC warming above pre-industrial levels), becoming high around warming of 2ºC, and very high beyond 2.5ºC.

The IPCC’s WG I provided an updated table (4.10) of “components in the Earth system that have been proposed as susceptible to tipping points/abrupt change, irreversibility, projected 21st Century change”. This table includes 15 items, including some that do not fall under the definition of a tipping point, e.g. global sea level rise (an outcome of ice sheet melting with no clear threshold for system reorganisation in itself).

Tipping-related knowledge and expertise outside of the academy is still limited, but growing. For example, international organisations like the OECD and World Meteorological Organization (WMO) are developing expertise and programmes with a focus on climate tipping (OECD, 2022), some scientific advisory bodies are building tipping-related capacity (Science Advisory Panel to Member States at the WMO Executive Council). These growing knowledge-production efforts need to be translated into tangible decision-making support for governments and other actors.

At this point, ESTPs only play a minor role in scientific assessments, policy debates and public discourse, and stakeholders are not making good use of available scientific knowledge. Widespread lack of awareness and misconceptions around tipping points (Milkoreit, 2015; 2019 limit the perceived need and corresponding demand for knowledge about ESTPs among policymakers. In this situation, scientific knowledge production also tends to be insufficient (Weichselgartner and Kasperson, 2010).

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