The Atlantic Ocean circulation that keeps northern Europe mild, the Greenland and Antarctic ice sheets, and the Southern Ocean upwelling that drives global nutrient cycles are all approaching potential tipping points—and this project will determine exactly when and how they might flip into new, irreversible states. Current climate models used for international assessments lack the ability to simulate ice-sheet collapse or ocean circulation shutdown as coupled systems. This project fills that gap by linking ice-sheet models to regional ocean and atmosphere models, then forcing them with outputs from the UK Earth System Model and global climate simulations. It will identify the temperature thresholds—tied to the Paris Agreement’s 1.5°C and 2°C targets—at which each tipping element becomes unstoppable. If successful, the research will produce early warning indicators that can be tested against real observational records, giving governments and coastal infrastructure planners decades of advance notice before, for example, the Greenland ice sheet commits to metres of sea-level rise. It will also map how tipping cascades—such as Southern Ocean changes destabilising Antarctic ice, or Greenland meltwater weakening the Atlantic circulation—amplify regional impacts on monsoon patterns and storm surge risks for cities like London, New York, and Shanghai.
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The aim of this project is to understand the processes controlling key tipping points (TPs) associated with the oceans and ice sheets, and assess their potential impacts on society and the global Earth system. The specific Tipping Elements (TEs) to be considered are related to the Atlantic Ocean Meridional Overturning (AMOC), the Greenland ice sheet (GrIS), coastal upwelling in the Southern Ocean (SO) and the Antarctic ice sheet (AIS). These TEs are a coherent subset of the TEs widely discussed in the literature. They (a) share relatively long timescales and therefore similar analysis methodologies are likely to be appropriate; (b) are potentially linked in tipping cascades such as the SO circulation interacting with AIS instability and GrIS meltwater impacting AMOC stability, as well as potential bi-polar interactions; and (c) share the hugely important impact of sea level rise. Work Package 1 focuses on AMOC and GrIS and their interaction; while Work Package 2 focuses on AIS and interactions with the SO. The overall objective in both is to constrain the circumstances under which the relevant TEs either have been or could potentially be triggered in the future; as well as addressing the long-term response of the TE to assess, in particular, under what circumstances the tipping becomes truly irreversible. These improvements in understanding lead into the identification of potential Early Warning indicators in Work Package 3, while Work Package 4 will assess the societal and climatic impacts of tipping focusing on projected regional sea level rise and global climate. The Topic A call identifies five research questions, all of which should be tackled. What are the global and regional impacts and risks associated with key climate TPs? Work Package 4 focuses on impact, in particular the key impact of regional sea level rise with links to the communities designing storm surge barriers and developing adaptive management approaches. This work package will also investigate the wider impacts of tipping on global climate using UKESM, for instance on changing monsoon patterns. Is there evidence for abrupt changes and TPs in the latest ESMs? Many of the current generation of ESMs (in particular those used in CMIP6) do not contain the appropriate coupling for ice sheet TPs so that we will use models of the ice sheets either as standalone or coupled to regional ocean and atmosphere models to assess tipping. Forcing for these experiments will come from both UKESM and the wider CMIP6 ensemble. How do the risks of TPs vary in scenarios that overshoot the Paris 1.5°C and 2°C targets? Our Work Packages 1 and 2 will determine thresholds for tipping for TPs associated with both ice sheets and the Atlantic Meridional Overturning Circulation, which can then be related back to the Paris targets. How do we design the best early warning systems for specific TPs such as Atlantic meridional overturning circulation shutdown, ice-sheet collapse, or forest dieback? Our approach in Work Package 3 is to test a range of statistical early warning indicators by applying them to the outputs of models that are known to tip to determine which indicators are able to predict this tipping and on what timescales. Where is there evidence of changing system resilience in observational records? Having tested these indicators, Work Package 3 will apply them to observational records.
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