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Climate tipping elements are large-scale subsystems of the Earth that may transgress critical thresholds (tipping points) under ongoing global warming, with substantial impacts on the biosphere and human societies. Frequently studied examples of such tipping elements include the Greenland Ice Sheet, the Atlantic Meridional Overturning Circulation (AMOC), permafrost, monsoon systems, and the Amazon rainforest. While recent scientific efforts have improved our knowledge about individual tipping elements, the interactions between them are less well understood. Also, the potential of individual tipping events to induce additional tipping elsewhere or stabilize other tipping elements is largely unknown. Here, we map out the current state of the literature on the interactions between climate tipping elements and review the influences between them. To do so, we gathered evidence from model simulations, observations, and conceptual understanding, as well as examples of paleoclimate reconstructions where multi-component or spatially propagating transitions were potentially at play. While uncertainties are large, we find indications that many of the interactions between tipping elements are destabilizing. Therefore, we conclude that tipping elements should not only be studied in isolation, but also more emphasis has to be put on potential interactions. This means that tipping cascades cannot be ruled out on centennial to millennial timescales at global warming levels between 1.5 and 2.0 ∘C or on shorter timescales if global warming surpassed 2.0 ∘C. At these higher levels of global warming, tipping cascades may then include fast tipping elements such as the AMOC or the Amazon rainforest. To address crucial knowledge gaps in tipping element interactions, we propose four strategies combining observation-based approaches, Earth system modeling expertise, computational advances, and expert knowledge.

This chapter assesses scientific evidence for tipping points across circulations in the ocean and atmosphere. The warming of oceans, modified wind patterns and increasing freshwater influx from melting ice hold the potential to disrupt established circulation patterns. We find evidence for tipping points in the Atlantic Meridional Overturning Circulation (AMOC), the North Atlantic Subpolar Gyre (SPG), and the Antarctic Overturning Circulation, which may collapse under warmer and ‘fresher’ (i.e. less salty) conditions. A slowdown or collapse of these oceanic circulations would have far-reaching consequences for the rest of the climate system, such as shifts in the monsoons. There is evidence that this has happened in the past, having led to vastly different states of the Sahara following abrupt changes in the West African monsoon, which we also classify as a tipping system. Evidence about tipping of the monsoons over South America and Asia is limited, however large-scale deforestation or air pollution are considered as potential sources of destabilisation. Although theoretically possible, there is little indication for tipping points in tropical clouds or mid-latitude atmospheric circulations. Similarly, tipping towards a more extreme or persistent El Niño Southern Oscillation (ENSO) state is not sufficiently supported by models and observations. While the thresholds for many of these systems are uncertain, tipping could be devastating for many millions of people. Stabilising climate (along with minimising other pressures, like aerosol pollution and ecosystem degradation) is critical for reducing the likelihood of reaching tipping points in the ocean-atmosphere system.

This chapter reviews interactions between climate tipping systems and assesses the potential risk of cascading effects. After a definition of tipping system interactions, we map out the current state of the literature on specific interactions between climate tipping systems that may be important for the overall stability of the climate system. For this, we gather evidence from model simulations, observations and conceptual understanding, as well as archetypal examples of palaeoclimate reconstructions where propagating transitions were potentially at play. This chapter concludes by identifying crucial knowledge gaps in tipping system interactions that should be resolved in order to improve risk assessments of cascading transitions under future climate change scenarios.

Abstract. We present a global atlas of downcore foraminiferal oxygen and carbon isotope ratios available at https://doi.org/10.1594/PANGAEA.936747 (Mulitza et al., 2021a). The database contains 2106 published and previously unpublished stable isotope downcore records with 361 949 stable isotope values of various planktic and benthic species of Foraminifera from 1265 sediment cores. Age constraints are provided by 6153 uncalibrated radiocarbon ages from 598 (47 %) of the cores. Each stable isotope and radiocarbon series is provided in a separate netCDF file containing fundamental metadata as attributes. The data set can be managed and explored with the free software tool PaleoDataView. The atlas will provide important data for paleoceanographic analyses and compilations, site surveys, or for teaching marine stratigraphy. The database can be updated with new records as they are generated, providing a live ongoing resource into the future.

The Atlantic Multidecadal Oscillation (AMO) is coherently linked to climate variations over many parts of the globe. Despite recent achievements, the mechanism by which the AMO influences regional precipitation over South America is not well understood. In this study, we isolate the atmospheric response to the AMO using a water isotope-enabled version of the Community Earth System Model version 1.2 (iCESM1.2) and determine its influence on (sub)tropical South American regional precipitation and atmospheric circulation. The results suggest an interhemispheric seesaw in Hadley circulation strength and that the section of the Atlantic Hadley cell is marked by a stronger upward air component south of the equator during the cold AMO phase. We also find that the precipitation anomalies over (sub)tropical South America during AMO phases are mainly related to changes in the Atlantic Intertropical Convergence Zone (ITCZ) core strength, where in the cold (warm) AMO phase the core region strengthens (weakens) from February to July, while from July to November the core region weakens (strengthens). Our results stress the importance of acknowledging the dynamics of season- and regional-dependent ITCZ responses, as they are sufficient to produce observed AMO-related signals even in the absence of marked changes in the ITCZ position.

Various mechanisms were proposed as substantial drivers of (sub)tropical South American hydroclimate changes during the last deglaciation. However, the interpretation of past precipitation records from the regions affected by the South American Summer Monsoon, the dominant hydroclimatic system in (sub)tropical South America, still insufficiently consider feedbacks between oceanic and atmospheric processes evident in modern observational data. Here, we evaluate ocean-atmosphere feedbacks active in the region from 19 to 4 ka based on a multi-proxy record comprising lipid biomarker, bulk sediment elemental composition and foraminiferal geochemistry from a sediment core retrieved from the tropical western South Atlantic offshore eastern Brazil at ~22 degrees S. Our proxy data together with existing paleoclimate records show that the consideration of large scale synoptic climatic features across South America is crucial for understanding the past spatio-temporal rainfall variability, especially during the last deglaciation. While the paleohydrological data from our study site show relatively stable precipitation across the deglaciation in the core region of the South Atlantic Convergence Zone, distinct hydroclimatic gradients developed across the continent during Heinrich Stadial 1, which climaxed at ~16 ka. By then, the prevalent atmospheric and oceanic configuration caused more frequent extreme climatic events associated with positive rainfall in the northern portion of eastern South America and in the southeastern portion of the continent. These climatic extremes resulted from substantial warming of the sub(tropical) western South Atlantic sea surface that fostered oceanic moisture transport towards the continent and the reconfiguration of quasi-stationary atmospheric patterns. We further find that enhanced continental precipitation in combination with low glacial sea level strongly impacted marine ecosystems via enhanced terrigenous organic matter input in line with

Paleoclimate records from tropical South America typically show precession-paced variability in rainfall, caused by insolation-driven changes in the South American Monsoon System, however this mechanism may not be responsible for hydroclimate change outside of the core monsoon domain, such as in the coastal zone of tropical eastern Brazil. Our findings are based on a similar to 850 kyr-long multiproxy record from a marine sediment core collected from the eastern Brazilian margin that represents the longest continuous record of South American hydroclimate to date. Utilizing the ln (K/Al) chemical weathering proxy from the core, we determine that past hydroclimate change in the coastal zone was primarily modulated by obliquity forcing. We demonstrate that high obliquity is associated with an increase in the boreal summer interhemispheric insolation contrast which decreases the zonality of the southern trade winds and reduces moisture advection to the coastal zone. Based on the long-term coherence between the ln (K/Al) record and benthic delta C-13 records from the Atlantic during Marine Isotope Stages 16-13, we infer that an increase in the strength of the overturning circulation, caused by Northern Hemisphere high-latitude forcing, may have produced surface cooling in the western tropical South Atlantic which led to reduced moisture advection to the coastal zone. We suggest that this mechanism may have also caused the amplification in millennial-scale variability in the coastal hydroclimate system, which began after the decoupling of the coastal hydroclimate system from obliquity forcing.