Emerging evidence on the potential crossing of climate systems “tipping points” at lower levels of warming than previously thought makes clear that immediate and accelerated emissions reductions are needed to avoid potentially catastrophic climate impacts. This chapter reviews the latest scientific evidence, providing an overview of major climate tipping points, their projected impacts if crossed, and the warming thresholds at which this becomes likely. It also considers policy options for managing tipping point risks: while efforts to keep global warming to 1.5°C with minimal overshoot are paramount, some tipping points may be crossed at lower warming thresholds and so transformational adaptation may also be necessary.
Net Zero+
Climate and Economic Resilience in a Changing World
2. Climate system tipping points and the need for urgent climate action
Abstract
This chapter draws on contributions to the Horizontal Project carried out under the responsibility of the Environment Policy Committee.
The Intergovernmental Panel on Climate Change (IPCC) delivered a stark warning of the extreme urgency of the climate challenge in its Sixth Assessment Report, projecting that severe climate impacts could occur in many regions of the world at lower levels of warming than previously thought (IPCC, 2021[1]). Climate change will lead to an increased frequency and intensity of extreme weather events as well as “slow onset” effects such as sea-level rise and changes in precipitation. A less well-understood impact of climate change are “tipping points” in the climate system and the potential for the thresholds of these critical points to be crossed.
What are climate system tipping points and how soon could they occur?
Overview and evolution of the scientific understanding of tipping points
The IPCC defines a tipping point as “a critical threshold beyond which a system reorganises, often abruptly and/or irreversibly”. A tipping element is “a component of the Earth system that is susceptible to a tipping point” (Chen et al., 2021[2]). Climate system tipping points may lead the global or regional climate to change from one stable state to another, or result in changes that occur non-linearly and faster than the rate of change expected from climate forcing (Alley et al., 2003[3]; Lee, 2021[4]).1 Such abrupt and/or irreversible changes are particularly dangerous because they can occur in timeframes short enough to defy the ability and capacity of human societies to adapt. As such, the impacts of crossing climate tipping point thresholds would be severe and widespread, with potentially catastrophic consequences for human and natural systems.
Tipping elements have been identified in three types of climate sub-systems: the cryosphere (ice bodies); circulations of the oceans and the atmosphere (circulation patterns); and the biosphere. Key examples include the collapse of the West Antarctic and Greenland ice sheets and the melting of the Arctic permafrost (cryosphere); the slowdown or collapse of the Atlantic Meridional Overturning Circulation (circulation patterns); and the dieback of the Amazon rainforest and destruction of coral reefs (biosphere). (For more detail on major tipping elements see Box 2.1.)
Figure 2.1. Candidate tipping elements in climate subsystems
Note: Arrows show potential interactions among the tipping elements that could generate tipping cascades, based on expert elicitation.
The issue of climate tipping points was first introduced by the IPCC over two decades ago, when they were projected to possibly occur in “the next few centuries if greenhouse gas concentrations continue to increase” (IPCC, 2001[9]). More recent IPCC reports recognise the risk of crossing tipping point thresholds at much lower levels of warming and therefore within considerably shorter timescales (IPCC, 2018[10]; IPCC, 2019[11]). Indeed, the latest IPCC report recognises that the possibility of crossing the thresholds of climate tipping points cannot be ruled out this century and must be an integral part of risk management strategies (IPCC, 2021[1]).
A recent synthesis of the most up-to-date evidence on tipping points shows that current global warming of ~1.1°C could already be within the lower end of the uncertainty range of five climate system tipping points, including the collapse of the Greenland and West Antarctic ice sheets, die-off of low-latitude coral reefs, and widespread abrupt permafrost thaw (McKay et al., 2022[12]). This means that crossing the thresholds of these tipping points is already “possible” (Ibid). The same study shows that within the Paris Agreement range of 1.5 to < 2°C warming, these climate tipping points and two others (abrupt Barents Sea ice loss and Labrador-Irminger Seas/SPG convection collapse) become “likely”. While not yet scientific consensus, these findings challenge the previously well-accepted assumption that climate system tipping points are low likelihood outcomes (OECD, 2022[13]).
To restate: the most recent findings thus suggest that the thresholds of many climate tipping points could be crossed with a considerably higher probability and at much lower levels of warming than previously thought. Scientific advances increasingly and systematically point to the potentially catastrophic impacts of continued warming, with evidence that irreversible tipping elements in Earth systems could already be triggered this century. This will have long-lasting effects over a timeframe of centuries to millennia (Lee, 2021[4]).
Figure 2.2. Global warming threshold estimates for global core and regional impact climate tipping elements
Note: Shadowed in green is the 1.5°C-2°C Paris Agreement range of warming. The shadowed area in grey shows the estimated 21st-century warming under current policies (horizontal line shows central estimates). Bars show the minimum (base, yellow); central (line, red); and maximum (top, dark red) threshold estimates for each tipping element (bold font, global; regular font, regional).
Source: (McKay et al., 2022[12]).
Figure 2.1 and Table 2.1 show the temperature range at which a number of tipping elements may be triggered – that is, ranges of temperature within which change in these tipping elements is strong enough to self-propel them.2 Despite significant scientific advances in reducing these ranges over past decades, uncertainty remains. Considering that larger uncertainties can potentially lead to a larger range of potential climate risks, they should amplify – not weaken – the case for strong climate action (OECD, 2021[5]).
Table 2.1. Temperature thresholds and uncertainty ranges of tipping points
Note: Literature-based temperature threshold estimates, including a central estimate and an uncertainty range for crossing of key tipping elements of the climate system. Central estimate column colour codes: red, dark orange and light orange denoting, respectively, central global warming threshold are within the Paris Agreement range of 1.5-2°C, within temperature range in line with current policies (2-4°C) and 4°C and above. Range column colour codes: red, dark orange and light orange denote respectively that current warming already within uncertainty range, levels in line with the Paris Agreement range within uncertainty range and range above Paris Agreement range. Compared to previous characterisation of tipping elements in the literature, the following tipping elements had not yet been featured: Labrador-Irminger Seas /SPG Convection (collapse), East Antarctic Subglacial Basins (collapse), Barents Sea Ice (abrupt loss). Information on potential to cause abrupt change and irreversibility, including timescales, and timescales from IPCC AR6 ( (Lee, 2021[4]), Table 4.10). IPCC confidence levels of potential to cause abrupt change reflect the author team’s judgement about the validity of the findings by an evaluation of evidence and agreement (Lee, 2021[4]).
Source: (McKay et al., 2022[12]; Lee, 2021[4]).
Evidence that climate tipping points may be approaching is increasing and has led scientists to declare a climate and ecological emergency (Lenton et al., 2019[14]; Ripple, 2020[15]).. For example, irreversible loss of part of the West Antarctic ice sheet may have already begun (Good et al., 2018[16]) and the Greenland ice sheet may also reach a tipping point whereby irreversible loss begins at 1.5°C of warming (Lenton et al., 2019[14]). Ocean ecosystems are already experiencing large-scale changes. For example, ocean heatwaves and acidification are causing mass bleaching of warm-water coral reefs; at warming above 2°C, 99% of coral reefs are projected to be lost (Lenton et al., 2019[14]). In addition, the Atlantic Meridional Overturning Circulation (AMOC) has been slowing over the past two decades (Good et al., 2018[16]) and is at its weakest for over a millennium (Caesar et al., 2021[17]; Boers, 2021[18]). Recent evidence that deforestation – itself a key contributor to climate change – combined with a warming climate, raises the probability that the Amazon will already shift from a humid to dry state during the 21st century (Lenton et al., 2019[14]; Arias et al., 2021[19]). If triggered, these tipping points would lead to often abrupt and irreversible impacts with potentially cascading global implications, including triggering of further tipping points, with dramatic effects on human and natural systems (Lenton et al., 2019[14]).
The possibility of tipping point cascades
If triggered, climate system tipping points may lead to changes in the regional or global climate. At a regional level, individual tipping points are associated with potentially severe local impacts such as extreme temperatures and higher frequency of droughts, forest fires and unprecedented weather. At the global level, due to atmospheric and ocean circulation, tipping elements are not isolated systems; rather, they interact. This means that the tipping of one element has the potential to trigger others (Lenton et al., 2019[14]; Wunderling et al., 2021[8]). Such cascading effects – when crossing the threshold of one tipping point triggers further tipping elements – could lead to a “hothouse” global climate that would be less suitable for human existence (Steffen et al., 2018[20]; Lenton et al., 2019[14]). The potential impacts of selected climate tipping points are summarised in Table 2.2.
Table 2.2. Potential impacts of selected tipping points
Source: (OECD, 2021[5]; McKay et al., 2022[12]).
The impacts of crossing tipping point thresholds can also cascade through socio-economic and ecological systems, often rapidly. They would intensify a range of climate hazards such as droughts, floods and other extreme weather events, causing direct damage to infrastructure and impacts on ecosystems, and water and food systems. These would, in turn, affect socio economic systems with impacts that could then propagate across sectors and international borders via global trade, financial flows and supply networks. Socio-economic responses to such impacts may themselves be non-linear, tipping socio-economic subsystems into a different state, inducing migration or political instability. Socio-economic responses can also result in positive or negative feedback effects with the climate system, either increasing emissions or accelerating mitigation action, thus potentially affecting further tipping elements.
Box 2.1. Overview of selected tipping points and their impacts
Collapse of the Atlantic Meridional Overturning Circulation (AMOC)
The Atlantic Meridional Overturning Circulation (AMOC) drives part of the ocean circulation through fluxes of heat and freshwater. While the AMOC has been relatively stable for several millennia, recent observations reveal that it is weakening and is currently at its weakest point in over 1 000 years. Early‑warning signals suggest that the AMOC is losing stability and is close to a critical transition (Boers, 2021[18]). This is driven by high melt rates of the Greenland ice sheet, demonstrating the interlinkages between tipping elements and potential for cascading effects (Wunderling et al., 2021[8]).
A collapse of the AMOC would represent a complete reorganisation of ocean circulation, with dramatic impacts on the climate system (OECD, 2021[5]). It would lead to a redistribution of heat around the planet and shifting rainfall patterns affecting sea ice, global sea levels, agricultural systems, and marine and terrestrial ecosystems (OECD, 2021[5]). Paleo records show that, in the past, changes in the strength of the AMOC have played a prominent role in transitions between warm and cool climatic phases (OECD, 2021[5]). In addition, changes in surface temperatures and precipitation patterns induced by an AMOC collapse or weakening have the potential to affect other tipping elements of the climate system, specifically the stability of the Amazon and boreal forests as well as the global monsoon system (Wunderling et al., 2021[8]). Even if a collapse does not occur, further weakening of the AMOC would still have major impacts, essentially a scaled-down version of those resulting from a complete collapse (OECD, 2021[5]).
Amazon and boreal forest dieback
The close association between land surface and water cycles makes the Amazon potentially susceptible to abrupt change (Douville et al., 2021[21]). A number of studies indicate that climate change (Cox et al., 2000[22]) and deforestation (Boers et al., 2017[23]), especially when combined, can lead to changes that would push the Amazon past a critical threshold beyond which a wide-scale ecosystem collapse becomes inevitable and tropical forest would gradually turn to a drier savannah state. While there is uncertainty regarding temperature thresholds at which this would occur, it is projected that continued Amazon deforestation, combined with a warming climate, raises the probability of crossing a tipping point in the state of the Amazon already this century (Arias et al., 2021[19]). The impacts associated with the dieback of the forest could be severe and of global scale. This has profound implications for biodiversity and ecosystem function, and dire consequences for local communities, in particular indigenous populations (Pörtner et al., 2022[24]).
Boreal forests are an integral component of regional and global climate systems that affect biosphere‑atmosphere interactions as well as large-scale circulation patterns. They are expected to experience the largest increase in temperatures of all forest biomes during the 21st century. The latest IPCC report assesses with high confidence that warmer and drier conditions have increased tree mortality and forest disturbances in many temperate and boreal biomes, negatively impacting provisioning services (Pörtner et al., 2022[24]). The impacts associated with a potential dieback of the boreal forest would be severe locally and globally. Local communities and economies that rely on the forests are particularly at risk. At the global level, boreal forest dieback would have implications for the long-term provisioning of global climate regulation through the exchange of energy and water.
Abrupt permafrost collapse
The release of carbon dioxide and methane from permafrost thaw into the atmosphere due to global warming and its impacts leads to an amplification of surface warming. Known as permafrost carbon feedback (PCF), carbon release following permafrost thaw is irreversible over centennial timescales (Canadell et al., 2021[25]). The PCF has been hypothesised to have substantial implications for greenhouse gas (GHG) emissions and the potential for abrupt permafrost thaw is considered a major tipping element of the Earth system (Lenton et al., 2019[14]). A total collapse of permafrost would release up to 888 Gt of carbon dioxide and 5.3 Gt1 of methane over this century (Canadell et al., 2021[25]). By comparison, the remaining carbon budgets for maintaining warming below 1.5°C and 2°C2 are respectively 400 and 1150 Gt CO2 (Canadell et al., 2021[25]). Alongside the global PCF and its contribution to global GHG emissions and warming, a permafrost collapse would also pose risks to local ecosystems, human livelihoods, health and infrastructure. Permafrost thaw interacts with other climatic and human factors and leads to geomorphological alterations, hydrological regime shifts and biome shifts, with regional implications for the frequency and magnitude of floods and landslides, coastal erosion, and hydrological dynamics.
The Arctic is both the largest permafrost region and the fastest warming region on Earth. High Arctic regions have seen global warming levels more than double those of the global average and virtually all climate scenarios project widespread permafrost warming and thawing in the future. In addition to global warming, wildfires and heatwaves currently drive abrupt permafrost thaw processes, exposing several meters of permafrost carbon on very short timescales. These are projected to increase in frequency in the Arctic region. There is also evidence that a synchronous large-scale permafrost collapse could occur due to abrupt permafrost drying and self-sustained internal heat production inside carbon-rich permafrost grounds – also known as “compost-bomb instability” (Hollesen et al., 2015[26]; McKay et al., 2022[12]). It is estimated that the temperature threshold for an abrupt regional permafrost thaw lies between 1°C and 2.3°C (best estimate at 1.5°C), while the large-scale collapse of permafrost is estimated to likely occur at higher warming levels of 3 to 6°C (McKay et al., 2022[12]).
Greenland ice sheet meltdown and West Antarctic ice sheet collapse
Improved data and models of ice sheet behaviour have recently revealed unexpectedly high melt rates in the Earth’s ice sheets. The Greenland and Antarctic ice sheets are being destabilised by several processes linked with global warming. There is now high scientific agreement on the existence of tipping points after which the Greenland and West Antarctic ice sheets irreversibly disintegrate. Different models have given critical temperature thresholds for a collapse of the Greenland ice sheet ranging from 1.5°C to 2.7°C (McKay et al., 2022[12]). Several studies highlight increasing evidence of an instability threshold for the West Antarctic ice sheet already at warmings levels of 1°C to 3°C, with a most probable estimate at 1.5°C (McKay et al., 2022[12]). The Greenland and Antarctic ice sheets are already major contributors to sea level rise. In the case of a collapse, these two tipping elements combined will lead to more than one additional metre of sea-level rise over this century. Additionally, the Greenland ice sheet and AMOC tipping elements are intimately interlinked, and Greenland ice sheet mass loss is already contributing to the weakening of the AMOC, with further mass loss potentially leading to an AMOC tipping point.
Arctic sea ice loss
Arctic summer and winter sea ice are declining fast under global warming. At warming levels of 1.5°C to 5°C, the Arctic will remain covered by winter sea ice over the course of this century, though to a lower extent. Above these warming levels, an abrupt collapse of the Arctic winter sea ice has been projected by several models. Such abrupt changes are driven by local positive feedbacks as the loss of sea ice reduces solar radiation reflection and increases temperatures locally. This makes Arctic winter sea ice collapse a credible tipping-point candidate. The likely threshold at which this tipping point would be crossed has been estimated at 6.3°C (McKay et al., 2022[12]). There are, however, many other models that show that the Arctic Sea ice responds linearly to global warming levels without any irreversibility in changes (Fox-Kemper et al., 2021[27]). There is therefore still a debate on whether the Arctic sea ice is susceptible to a tipping point or not.
Changes in sea ice impact exchanges of energy fluxes between the atmosphere and the ocean, thereby influencing atmospheric, oceanic and climatic conditions. Through changes to the surface-albedo feedback, which results from solar radiation reflection on the Earth’s surface, sea ice loss amplifies warming. A collapse of year-round Arctic sea ice could lead to up to 0.6°C of additional warming globally. Surface-albedo feedbacks due to the loss of sea ice have already played an important role in the amplification of warming in the Arctic. Arctic sea ice loss is thereby contributing to losses in other components of the cryosphere, accelerating permafrost thaw rates and Arctic ice sheet surface melt The loss of Arctic sea ice will also contribute to ocean acidification (Canadell et al., 2021[25]) and threaten polar ecosystems and local livelihoods.
1. Or 143 Gt CO2-eq.
2. The IPCC’s remaining carbon budgets from 2020 onwards for maintaining warming below these levels by the end of the century with a 67% chance.
Source: Summary of more extensive literature review provided in (OECD, 2022[28]).
Incorporating climate tipping points into economic modelling3
Socio-economic systems also exhibit non-linearities and their own potential tipping points when subjected to worsening climate impacts. Yet models that underpin most economic analyses of climate change rarely include the possibility of abrupt changes to climate or economic systems (Rose, 2022[29]).
A comprehensive review of the literature highlights that economic modelling that includes tipping points has not informed climate policy in a substantive way (Kopits, Marten and Wolverton, 2013[30]). This is largely because modelling efforts that included large-scale singular events were based on Integrated Assessment Models (IAMs) that used ad hoc parameters without empirical bases and typically without considering the multi-decade time horizons at which such large-scale events could unfold. Recent efforts have attempted to more accurately incorporate physical science into economic models and better capture the dynamics of Earth systems and their associated uncertainties (Nordhaus, 2019[31]; Yumashev et al., 2019[32]; Kikstra et al., 2021[33]). As an interesting example, Dietz et al. (2021[34]) provide estimations for the impacts of different tipping points on the social cost of carbon (SCC),4 proposing a meta-analytic IAM that includes eight climate tipping points under a unified framework. They find that, taken collectively, tipping points increase the SCC by around 25% and, importantly, that they increase global economic risk.
Efforts have also been made to take interactions between tipping points into account. Models wherein the crossing of one tipping point threshold increases the probability of another tipping point result in substantially increased SCC (Cai, Lenton and Lontzek, 2016[35]) (Lemoine and Traeger, 2016[36]). Given the uncertainties in the timing and biophysical effects of tipping points in the scientific literature, factoring uncertainty into economic models is also essential. Models that include the uncertainty of economic and climate risks also result in large effects on the social cost of carbon (Cai and Lontzek, 2019[37]) (Cai, Lenton and Lontzek, 2016[35]).
To better understand the cost of climate system tipping points, economic models of climate tipping points should account not only for changes in global mean temperature but also for other physical climate or weather elements (e.g. water cycle, radical changes in the seasonality of extreme events, etc.). There is also a need for improved tipping metrics that consider, for instance, some interval of temperatures. Finally, to improve the coupling of economic and geophysical models, researchers should start with a recursive/simulation model and only then move to optimisation models. There seems to be merit in performing simulation, not optimisation-based models, to achieve a better sense of expected damages.
Finally, climate impacts including tipping points are also inextricably linked to socio-economic systems. There is a clear need to better understand these interlinkages. This includes, for example, modelling the impacts of climate change on financial stability (Kiley, 2021[38]) (Lamperti et al., 2020[39]) (Lamperti et al., 2019[40]); the macroeconomic implications of the transition to net zero (Pisani-Ferry, 2021[41]); regional differences in macroeconomic impacts (Batten, forthcoming[42]); and interactions between impacts across different economic sectors.
Policy responses to address the risk of climate tipping points
Global policy efforts and actions that explicitly target risks associated with the triggering of climate system tipping points and their potential cascading effects remain intangible and highly insufficient. It is imperative to assess how the latest knowledge on climate tipping points can inform risk-management strategies today, including the mitigation of greenhouse gas emissions and net-zero transition strategies; adaptation to climate change and building resilience to accelerating potential climate impacts; and technological development and innovation.
Accelerating mitigation strategies
Fully integrating the risks associated with climate tipping points into climate risk management strategies requires a precautionary approach to mitigation. Considering that some tipping points may already be triggered between 1.5 and 2°C of warming, this means limiting the temperature increase to 1.5°C, with no or very limited overshoot. Indeed, an overshoot of the 1.5°C limit could result in a considerably higher risk of crossing climate tipping-point thresholds even if temperatures return to 1.5 °C levels by the end of this century (OECD, 2022[28]).
The estimated possibility of climate system tipping points effectively limits the number and shape of emissions pathways towards 1.5°C of warming and renders lenient interpretations of the Paris Agreement goal significantly more dangerous. Limiting warming to 1.5°C with no or very limited overshoot requires urgent acceleration of near-term action to reach net-zero CO2 emissions. It is therefore no longer “only” about achieving net-zero emissions by mid-century but how this can be achieved: rapid and deep emissions cuts must be made already this decade. As is, current policies in line with meeting countries’ Nationally Determined Contributions (NDCs) will not limit warming to 1.5°C without overshoot. It is critical that NDCs are strengthened before 2025, and that commensurate policies are implemented at relevant timescales to meet revised targets (OECD, 2022[28]).
It is also important to note that, if triggered, some climate tipping points would effectively reduce the remaining carbon budget for reaching temperature objectives. Indeed, loss of sea ice and ice sheets leads to a decrease of solar radiation reflection, raising surface temperatures. If these tipping points are crossed, emissions reductions would need to be even larger than previously thought to meet stated temperature targets. In addition, permafrost carbon emissions have already lowered the estimated remaining carbon budgets for achieving the 1.5°C and 2°C warming objectives, even without having reached the threshold for an abrupt tipping point (Canadell et al., 2021[25]). As most of these tipping elements are likely to be tipped already within the 1.5 to 2°C range, temperature feedback loops further stress how crucial it is to avoid or limit overshooting 1.5°C.
Moreover, for some tipping elements, climate and human disturbances outside GHG emissions can potentially interact with global warming and contribute to surpassing critical thresholds. For example, land use and hydrological changes alongside climate change could lead to widespread dieback of the Amazon rainforest in the near term. In the Arctic, wildfires are increasingly contributing to abrupt permafrost thaw and carbon release from boreal forests.
Collective ambitious action to keep warming below 1.5°C is the safest and most cost-effective way to mitigate climate change and minimise the risk of triggering climate tipping points. The latest economic assessments show that when faced with the risk of cascading tipping points and their non-linear and irreversible impacts, the additional costs of implementing stringent climate policies earlier are worth paying. A rise of 1.5°C can still be achieved with very limited or no overshoot, although this requires a very rapid transformation of economies and societies, and a focus on a resilient and orderly transition (see Part II of this report). As emissions continue to rise, however, this window of opportunity is closing swiftly.
Building transformational resilience to climate impacts
Given the lower levels of warming at which the thresholds of climate system tipping points may be crossed, adaptation planning must account for the possibility of climate tipping points and their cascading impacts. The sheer magnitude of these possible impacts, coupled with their possibly abrupt and non-linear nature, requires more than just incremental adaptation efforts. To remain resilient, policy makers need to consider transformational adaptation actions. Even if the Paris Agreement’s temperature target is met, it is likely that some transformational adaptation will be needed (Ara Begum, 2022[43]). If mitigation efforts fall short of the 1.5°C target, transformational adaptation will be all the more important as impacts become more severe, and the risk of crossing tipping points increases (Ara Begum, 2022[43]).
Transformational adaptation means changing the fundamental characteristics of human and natural systems to increase their capacity to cope with potential hazards (IPCC, 2022[44]). In light of the threat of climate system tipping points, transformational adaptation could necessitate stringent and even drastic measures to reduce impacts and avoid losses. Such drastic measures, potentially transforming whole communities and economic sectors, will undoubtedly result in short-term disruptions. However, considering the immense cost of inaction in the face of tipping point impacts, transformational adaptation is worthwhile.
Transformational adaptation measures can be technological, for example, implementing water capture and storage solutions in areas at risk of drought. They can also be behavioural or include fundamental changes in institutional arrangements, priorities, and norms (Kates, Travis and Wilbanks, 2012[45]). They can also target the spatial development of human activities, such as managed retreat of communities and settlements, relocation of assets and infrastructure to less at-risk areas, long term spatial planning, and urban and agricultural zoning. Other examples include international co-operation among governments to manage migrations, the deployment of nature-based solutions (NbS), and livelihood transformation in land systems (New, 2022[46]).
A specific example is adapting energy planning and zoning in the Amazon region, which is heavily reliant on large-scale hydropower, to anticipate the impacts on the region’s hydrological cycle should the Amazon turn from rainforest to savannah. This includes decentralisation of energy production, diversification of energy sources focusing on small-scale hydropower and solar power, and investments in energy saving (Lapola et al., 2018[47]). A transformational approach to adaptation in the Amazon would also mean livelihood transformation, i.e. encouraging farmers to switch to crop varieties and livestock suitable for drier conditions in order to protect the agricultural sector (ibid).
Transformational adaptation measures that are beneficial or low-cost even if tipping points do not occur are “no-regret” policies (Heltberg, Siegel and Jorgensen, 2009[48]). Some may come with large co-benefits by contributing to reductions in GHG, supporting the advancement of other sustainable development goals (e.g. energy and water access), and building the resilience of systems and populations to future climate shocks. This is especially the case for investment in rehabilitating ecosystems and ecosystems services and the implementation of nature-based solutions, which are also important for accelerating mitigation efforts (Schipper et al., 2022[49]). (NbS are discussed further in Chapter 12.)
Many current adaptation initiatives prioritise near-term climate risk reduction and may even clash with efforts to bring about transformational adaptation (IPCC, 2022[37]). For example, building flood defences may lock in infrastructure development in areas that would be untenable if tipping points were crossed. Instead, to ensure societies’ resilience to climate-change impacts, especially those brought about by the crossing of tipping-point thresholds, transformational adaptation efforts must be pursued alongside stringent mitigation efforts to limit climate risk. Implementing transformative actions that support sustainable development goals is a key opportunity for climate resilient development.
Technology and innovation
Technological developments and innovation can also help to reduce and manage the risks associated with climate tipping points.
First, technologies for better monitoring and modelling of the climate system are essential to assess how climate-related hazards resulting from tipping points may evolve over time. In addition, it is difficult to predict the thresholds at which tipping points may be crossed, as the parameters that induce a shift often show only incremental changes before the system makes a sudden or persistent transition. Climate modelling and remote sensing are improving in their ability to detect early warning signals, but these new findings are not yet feeding into the risk management strategies informing policy makers. Greater efforts to make this information readily accessible is essential to addressing the threat of climate tipping points.
Second, technologies can help develop and implement ways to reduce and manage the risks of climate system tipping points. Carbon-dioxide removal (CDR) technologies are key, as scenarios that limit warming to 1.5°C with no or very limited overshoot all include some deployment of CDR. It is essential to note that CDR technologies are needed to accelerate early and deep emissions reductions and balance out harder to-abate sectors that continue to produce residual emissions during the first half of the century, but CDR technologies should not justify delayed mitigation action (Riahi et al., 2021[50]).
Moreover, there are legitimate concerns regarding CDR technologies, for example the immense demand for land and resulting implications for land-use practices that bioenergy with carbon capture and storage (BECCS) requires (Creutzig et al., 2021[51]). Questions also remain over the scalability of CDR. The potential trade-offs between the risks of employing CDR technologies – in particular BECCS – and the risks of triggering climate system tipping points if CDR technologies are not employed are poorly understood. Investments are needed to better understand these trade-offs and evaluate the risks associated with scaled-up use of CDR technologies or failure to employ them altogether.
Chapter conclusions
Mounting evidence that climate tipping point thresholds may be crossed sooner and at lower warming levels than previously thought means that every effort must be made to avoid this scenario. This requires an immediate acceleration of climate mitigation efforts, as even the most optimistic projections of current policy commitments are insufficient. Focusing solely on the goal of net-zero emissions by 2050 is not enough. Even if net-zero emissions by are achieved by 2050, it is still possible that certain tipping point thresholds will be crossed this century, even more so if the target of 1.5°C warming is overshot. Drastic, transformational adaptation efforts must be considered to ensure the resilience of climate policies in the face of future disruptions.
References
[3] Alley, R. et al. (2003), “Abrupt Climate Change”, Science, Vol. 299/5615, pp. 2005-2010, https://doi.org/10.1126/science.1081056.
[43] Ara Begum, R. (2022), “Point of Departure and Key Concepts”, in H.-O. Pörtner, D. (ed.), Climate Change 2022: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, In Press.
[19] Arias, P. et al. (2021), “Technical Summary”, in Masson-Delmotte, V. et al. (eds.), Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
[42] Batten, S. (forthcoming), “The impact of the weather on the UK economy”, Mimeo.
[18] Boers, N. (2021), “Observation-based early-warning signals for a collapse of the Atlantic Meridional Overturning Circulation”, Nature Climate Change, Vol. 11/8, pp. 680-688, https://doi.org/10.1038/s41558-021-01097-4.
[23] Boers, N. et al. (2017), “A deforestation-induced tipping point for the South American monsoon system”, Scientific Reports, Vol. 7/1, https://doi.org/10.1038/srep41489.
[17] Caesar, L. et al. (2021), “Current Atlantic Meridional Overturning Circulation weakest in last millennium”, Nature Geoscience, Vol. 14/3, pp. 118-120, https://doi.org/10.1038/s41561-021-00699-z.
[7] Cai, Y., T. Lenton and T. Lontzek (2016), “Risk of multiple interacting tipping points should encourage rapid CO2 emission reduction”, Nature Climate Change, Vol. 6/5, pp. 520-525, https://doi.org/10.1038/nclimate2964.
[35] Cai, Y., T. Lenton and T. Lontzek (2016), “Risk of multiple interacting tipping points should encourage rapid CO2 emission reduction”, Nature Climate Change, Vol. 6/5, pp. 520-525, https://doi.org/10.1038/nclimate2964.
[37] Cai, Y. and T. Lontzek (2019), “The Social Cost of Carbon with Economic and Climate Risks”, Journal of Political Economy, Vol. 126/6, pp. 2684-2734, https://www.journals.uchicago.edu/doi/full/10.1086/701890.
[25] Canadell, J. et al. (2021), “Global Carbon and other Biogeochemical Cycles and Feedbacks”, in Masson-Delmotte, V. et al. (eds.), Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
[2] Chen, D. et al. (2021), “Framing, Context, and Methods.”, in Masson-Delmotte, V. (ed.), Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change.
[22] Cox, P. et al. (2000), “Acceleration of global warming due to carbon-cycle feedbacks in a coupled climate model”, Nature, Vol. 408/6809, pp. 184-187, https://doi.org/10.1038/35041539.
[51] Creutzig, F. et al. (2021), “Considering sustainability thresholds for BECCS in IPCC and biodiversity assessments”, GCB Bioenergy, Vol. 13/4, pp. 510-515, https://doi.org/10.1111/gcbb.12798.
[34] Dietz, S. et al. (2021), “Economic impacts of tipping points in the climate system”, {Proceedings of the National Academy of Sciences, Vol. 118/34, https://doi.org/10.1073/pnas.2103081118.
[21] Douville, H. et al. (2021), “Water Cycle Changes”, in Masson-Delmotte, V. et al. (eds.), Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to 45 the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press.
[16] Good, P. et al. (2018), “Recent progress in understanding climate thresholds”, Progress in Physical Geography: Earth and Environment, Vol. 42/1, pp. 24-60, https://doi.org/10.1177/0309133317751843.
[29] H.-O. Pörtner, D. (ed.) (2022), Cross-Working Group Box ECONOMIC: Estimating Global Economic Impacts from Climate Change, Cambridge University Press.
[46] H.-O. Pörtner, D. (ed.) (2022), Decision Making Options for Managing Risk, Cambridge University Press.
[48] Heltberg, R., P. Siegel and S. Jorgensen (2009), “Addressing human vulnerability to climate change: Toward a ‘no-regrets’ approach”, Global Environmental Change, Vol. 19/1, pp. 89-99, https://doi.org/10.1016/j.gloenvcha.2008.11.003.
[26] Hollesen, J. et al. (2015), “Permafrost thawing in organic Arctic soils accelerated by ground heat production”, Nature Climate Change, Vol. 5/6, pp. 574-578, https://doi.org/10.1038/nclimate2590.
[44] IPCC (2022), “Summary for Policymakers”, in H.-O. Pörtner et al. (eds.), Climate Change 2022: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change . In Press., Cambridge University Press.
[1] IPCC (2021), “Summary for Policymakers”, in Masson-Delmotte, P. et al. (eds.), Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, In Press.
[11] IPCC (2019), “Summary for Policymakers”, in H.-O. Pörtner et al. (eds.), IPCC Special Report on the Ocean and Cryosphere in a Changing Climate, Intergovernmental Panel on Climate Change, Geneva.
[10] IPCC (2018), “Summary for Policymakers”, in Masson-Delmotte, V. et al. (eds.), Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate...., Intergovernmental Panel on Climate Change, Geneva.
[9] IPCC (2001), Climate Change 2001: Synthesis Report. A Contribution of Working Groups I, II, and III to the Third Assessment Report of the Integovernmental Panel on Climate Change, Watson, R.T. et al. (eds.), Cambridge University Press, Cambridge, United Kingdom, and New York.
[45] Kates, R., W. Travis and T. Wilbanks (2012), “Transformational adaptation when incremental adaptations to climate change are insufficient”, Proceedings of the National Academy of Sciences, Vol. 109/19, pp. 7156-7161, https://doi.org/10.1073/pnas.1115521109.
[33] Kikstra, J. et al. (2021), “The social cost of carbon dioxide under climate-economy feedbacks and temperature variability”, Environmental Research Letters, Vol. 16/9, p. 094037, https://doi.org/10.1088/1748-9326/ac1d0b.
[38] Kiley, M. (2021), “Growth at Risk From Climate Change”, Finance and Economics Discussion Series, Vol. 2021/054, pp. 1-19, https://doi.org/10.17016/feds.2021.054.
[30] Kopits, E., A. Marten and A. Wolverton (2013), “Moving Forward with Incorporating “Catastrophic” Climate Change into Policy Analysis”, NCEE Working Paper Series, Working Paper 13-01.
[6] Kriegler, E. et al. (2009), “Imprecise probability assessment of tipping points in the climate system”, Proceedings of the National Academy of Sciences, Vol. 106/13, pp. 5041-5046, https://doi.org/10.1073/pnas.0809117106.
[40] Lamperti, F. et al. (2019), “The public costs of climate-induced financial instability”, Nature Climate Change, Vol. 9/11, pp. 829-833, https://doi.org/10.1038/s41558-019-0607-5.
[39] Lamperti, F. et al. (2020), “Climate change and green transitions in an agent-based integrated assessment model”, Technological Forecasting and Social Change, Vol. 153, p. 119806, https://doi.org/10.1016/j.techfore.2019.119806.
[47] Lapola, D. et al. (2018), “Limiting the high impacts of Amazon forest dieback with no-regrets science and policy action”, Proceedings of the National Academy of Sciences, Vol. 115/46, pp. 11671-11679, https://doi.org/10.1073/pnas.1721770115.
[4] Lee, J. (2021), “Future Global Climate: Scenario-Based Projections and NearTerm Information”, in [Masson-Delmotte, V. (ed.), Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 553–672.
[36] Lemoine, D. and C. Traeger (2016), “Economics of tipping the climate dominoes”, Nature Climate Change, Vol. 6/5, pp. 514-519, https://doi.org/10.1038/nclimate2902.
[14] Lenton, T. et al. (2019), “Climate tipping points — too risky to bet against”, Nature, Vol. 575/7784, pp. 592-595, https://doi.org/10.1038/d41586-019-03595-0.
[27] Masson-Delmotte, V. et al. (eds.) (2021), Ocean, Cyroshphere and Seal Level Change, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
[12] McKay, A. et al. (2022), “Exceeding 1.5°C global warming could trigger multiple climate tipping points”, Science, Vol. 377/6611, https://doi.org/10.1126/science.abn7950.
[31] Nordhaus, W. (2019), “Economics of the disintegration of the Greenland ice sheet”, Proceedings of the National Academy of Sciences, Vol. 116/25, pp. 12261-12269, https://doi.org/10.1073/pnas.1814990116.
[13] OECD (2022), Climate tipping points: insights for effective policy action.
[28] OECD (2022), Climate Tipping Points: Insights for Effective Policy Action, OECD Publishing, Paris, https://doi.org/10.1787/abc5a69e-en.
[5] OECD (2021), Managing Climate Risks, Facing up to Losses and Damages, OECD Publishing, Paris, https://doi.org/10.1787/55ea1cc9-en.
[52] OECD (2018), “The social cost of carbon”, OECD Publishing, Paris, https://doi.org/10.1787/9789264085169-17-en.
[41] Pisani-Ferry, J. (2021), “Climate policy is macroeconomic policy, and the implications will be significant”, PIIE Policy Brief 21-20, https://www.piie.com/publications/policy-briefs/climate-policy-macroeconomic-policy-and-implications-will-be-significant.
[24] Pörtner, H. et al. (2022), “Technical Summary”, in Pörtner, H. et al. (eds.), Climate Change 2022: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press.
[50] Riahi, K. et al. (2021), “Cost and attainability of meeting stringent climate targets without overshoot”, Nature Climate Change, Vol. 11/12, pp. 1063-1069, https://doi.org/10.1038/s41558-021-01215-2.
[15] Ripple, W. (2020), “World scientists’ warning of a climate emergency.”, Bioscience, Vol. 70/1, pp. 8-12.
[49] Schipper, E. et al. (2022), “Climate Resilient Development Pathways”, in H.-O. Pörtner et al. (eds.), Climate Change 2022: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change., Cambridge University Press.
[20] Steffen, W. et al. (2018), “Trajectories of the Earth System in the Anthropocene”, Proceedings of the National Academy of Sciences, Vol. 115/33, pp. 8252-8259, https://doi.org/10.1073/pnas.1810141115.
[8] Wunderling, N. et al. (2021), “Interacting tipping elements increase risk of climate domino effects under global warming”, Earth System Dynamics, Vol. 12/2, pp. 601-619, https://doi.org/10.5194/esd-12-601-2021.
[32] Yumashev, D. et al. (2019), “Climate policy implications of nonlinear decline of Arctic land permafrost and other cryosphere elements”, Nature Communications, Vol. 10/1, https://doi.org/10.1038/s41467-019-09863-x.
Notes
← 1. Climate or radiative forcing is the change in energy flux in the atmosphere caused by natural or anthropogenic factors of climate change, such as greenhouse gas emissions or increased water vapour. It is a direct measure of the amount that the Earth’s energy budget is out of balance due to external drivers of change.
← 2. The latest IPCC report does not provide temperature thresholds for tipping per tipping element, but summarises levels of change according to different levels of temperature increase. For example, the report estimates that it is likely that under temperature levels of 1.5°C, 2.0°C or 3.0°C relative to 1850–1900, the Atlantic Meridional Overturning Circulation (AMOC) will continue to weaken for several decades by about 15%, 20% and 30% of its strength. In addition, at sustained warming levels between 2°C and 3°C, there is evidence, albeit limited, that the Greenland and West Antarctic ice sheets will be lost almost completely and irreversibly over multiple millennia. The probability of their complete loss and the rate of mass loss increases with higher surface temperatures (high confidence) (Arias et al., 2021[19])
← 3. This sub-section draws partially on the results of the OECD Expert workshop on Economic Modelling of Climate and Related Tipping Points held under the Net Zero+ project on 18-19 October 2021: https://www.oecd.org/env/indicators-modelling-outlooks/Workshop-Tipping-Points-Summary-Report.pdf.
← 4. The social cost of carbon (SCC) is the central concept for the inclusion of climate change damages in the cost-benefit analysis of public policy and public investments. It measures the present value in monetary terms of the damages incurred when an additional tonne of carbon (or any other greenhouse gas) is released into the atmosphere.