Impacts and State‐Dependence of AMOC Weakening in a Warming Climate

Geophysical Research Letters, Journal Year: 2024, Volume and Issue: 51(10)

Published: May 13, 2024

Abstract All climate models project a weakening of the Atlantic Meridional Overturning Circulation (AMOC) strength in response to greenhouse gas forcing. However, impacts AMOC decline alone cannot be isolated from other drivers change using existing Coupled Model Intercomparison Project simulations. To address this issue, we conduct idealized experiments EC‐Earth3 model. We compare an abrupt 4×CO 2 simulation with same experiment, except artificially fix at preindustrial levels. With design, can formally attribute differences between these two decline. In addition, quantify state‐dependence by comparing aforementioned which reduce strength. Our findings demonstrate that are state‐dependent, thus understanding on future requires targeted model experiments.

Language: Английский

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A multicentennial mode of North Atlantic climate variability throughout the Last Glacial Maximum

Science Advances, Journal Year: 2023, Volume and Issue: 9(44)

Published: Nov. 1, 2023

Paleoclimate proxy records from the North Atlantic region reveal substantially greater multicentennial temperature variability during Last Glacial Maximum (LGM) compared to current interglacial. As there was no obvious change in external forcing, causes for increased remain unknown. Exploiting LGM simulations with a comprehensive coupled climate model along high-resolution records, we introduce an oscillatory mode of variability, which is associated moderate variations meridional overturning circulation and depends on large-scale salinity distribution. This self-sustained amplified by sea-ice feedbacks induces maximum surface subpolar region. Characterized distinct climatic imprint different dynamics, oscillation has be distinguished Dansgaard-Oeschger emerges only under full forcing. The potential modes emerge or disappear response changing forcing may have implications future change.

Language: Английский

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Reflecting on the Science of Climate Tipping Points to Inform and Assist Policy Making and Address the Risks they Pose to Society

Surveys in Geophysics, Journal Year: 2024, Volume and Issue: unknown

Published: June 4, 2024

Abstract There is a diverging perception of climate tipping points, abrupt changes and surprises in the scientific community public. While such dynamics have been observed past, e.g., frequent reductions Atlantic meridional overturning circulation during last ice age, or sheet collapses, points might also be possibility an anthropogenically perturbed climate. In this context, high impact—low likelihood events, both physical realm as well ecosystems, will potentially dangerous. Here we argue that formalized assessment state science needed order to establish consensus on issue reconcile views. This has approach taken by Intergovernmental Panel Climate Change (IPCC). Since 1990, IPCC consistently generated robust several complex issues, ranging from detection attribution change, global carbon budget sensitivity, projection extreme events their impact. Here, suggest conducted collaboratively Science-Policy Platform Biodiversity Ecosystem Services, would represent ambitious yet necessary goal accomplished within next decade.

Language: Английский

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The Impact of CO₂ and Climate State on Whether Dansgaard–Oeschger Type Oscillations Occur in Climate Models

Geophysical Research Letters, Journal Year: 2024, Volume and Issue: 51(13)

Published: June 29, 2024

Abstract Greenland ice core records feature Dansgaard–Oeschger (D‐O) events, which are abrupt warming episodes followed by gradual cooling during age climate. The three climate models used in this study (CCSM4, MPI‐ESM, and HadCM3) show spontaneous self‐sustained D‐O‐like oscillations (albeit with differences amplitude, duration, shape) a remarkably similar, narrow window of carbon dioxide ( CO 2 ) concentration, roughly 185–230 ppm. This range matches atmospheric Marine Isotopic Stage 3 (MIS 3: between 27.8 59.4 thousand years BP, hereafter ka), period when D‐O events were most frequent. Insights from the point to North Atlantic (NA) sea‐ice coverage as key ingredient behind type oscillations, acts “tipping element.” Other state properties such Mean Meridional Overturning Circulation strength, global mean temperature salinity gradient Ocean do not determine whether behavior can occur all models.

Language: Английский

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A novel conceptual model for Dansgaard–Oeschger event dynamics based on ice-core data

Climate of the past, Journal Year: 2025, Volume and Issue: 21(1), P. 115 - 132

Published: Jan. 16, 2025

Abstract. This study introduces a novel dynamical systems model designed to capture the highly non-periodic nature of Dansgaard–Oeschger (DO) events. Such events are difficult adequately due their variable durations (some lasting around 1 century, while others span multiple millennia) and occurrence short precursor that precede longer DO despite similar boundary climate conditions. Utilising simplified two-equation framework derived from Stommel model, our approach integrates an internal control parameter which acts as feedback on Antarctic Bottom Water (AABW) formation. Through both analytical numerical methods, we establish suitable domain within newly adjusted models can accurately replicate palaeoclimatic records described by summary statistics ice-core data. The analysis also shows that, without parameter, does not have in it reproduce wide range event characteristics seen record. provides new insights into underlying mechanisms driving these significant phenomena necessary timescale they forced allowing model's parameters vary through time. allows achieve unprecedented precision capturing realistic sequence with timing matching those observational refined only enhances understanding cycles but demonstrates potential simple simulate complex interactions.

Language: Английский

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Atmospheric and Oceanic Pathways Drive Separate Modes of Southern Hemisphere Climate in Simulations of Spontaneous Dansgaard‐Oeschger‐Type Oscillations

Geophysical Research Letters, Journal Year: 2025, Volume and Issue: 52(5)

Published: Feb. 28, 2025

Abstract Dansgaard‐Oeschger (DO) events are a dominant mode of millennial‐scale climate variability during the last glacial period with most pronounced impacts in North Atlantic region. In Antarctica, they manifest primarily as muted and phase‐shifted temperature signal, but recent studies suggest an additional in‐phase component. Here, we analyze Southern Hemisphere (SH) response to spontaneous DO‐type oscillations general circulation model. The Antarctic is compared Greenland variations consistent oceanic pathway described by bipolar seesaw However, leading SH atmospheric varies synchronously temperatures. A westward‐shifted Walker strengthened Hadley cell maxima cause zonally heterogeneous jet stream anomalies differing from Annular Mode pattern. Comparison simulated O speleothems ice cores indicates good agreement tropics mid‐latitudes deviations Antarctica warrant further research.

Language: Английский

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A multi-model assessment of the early last deglaciation (PMIP4 LDv1): a meltwater perspective

Climate of the past, Journal Year: 2024, Volume and Issue: 20(4), P. 789 - 815

Published: April 5, 2024

Abstract. The last deglaciation (∼20–11 ka BP) is a period of major, long-term climate transition from glacial to interglacial state that features multiple centennial- decadal-scale abrupt variations whose root cause still not fully understood. To better understand this time period, the Paleoclimate Modelling Intercomparison Project (PMIP) has provided framework for an internationally coordinated endeavour in simulating whilst encompassing broad range models. Here, we present multi-model intercomparison 17 transient simulations early part (∼20–15 nine different models spanning model complexities and uncertain boundary conditions forcings. numerous available provide opportunity chain events mechanisms changes between 20 15 BP our collective ability simulate them. We conclude amount freshwater forcing whether it follows ice sheet reconstruction or induces inferred Atlantic meridional overturning circulation (AMOC) history, heavily impacts deglacial evolution each simulation rather than differences physics. course consistent except when above 0.1 Sv – at least 70 % agree there warming by most places excluding location meltwater input. For with forcings exceed 18 BP, delayed North surface air temperature correlations AMOC strength are much higher. However, find coming out Last Glacial Maximum (LGM) also plays key role sensitivity In addition, show response chosen scenario depends largely on other aspects experimental design (e.g. CO2 reconstruction). results insight into first how choices forcings, focus fluxes, can impact outputs. use these findings as helpful future period.

Language: Английский

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Campanian Ignimbrite tephra reveals asynchronous vegetation responses to abrupt climate change in the eastern Mediterranean region

Quaternary Science Reviews, Journal Year: 2024, Volume and Issue: 334, P. 108714 - 108714

Published: May 27, 2024

The timing and rate of ecosystem response to abrupt climate change is a product numerous complex interactions between biotic abiotic drivers. Palaeoecological studies from long sedimentary records, particularly those that span periods dynamic such as the last glacial cycle, can help contextualise responses variability through time. Detailed compare proxy data multiple sites, with high chronological precision, have potential ascribe mutual drivers, and, therefore, track spatiotemporal in responses. Here, we interrogate vegetation impact past eastern Mediterranean, using three sub-centennially resolved pollen archives Greece. widespread Campanian Ignimbrite (CI/Y-5; ca. 39.85 ka BP) tephra marker used an isochron directly correlate records Ioannina (NW Greece), Tenaghi Philippon (NE Megali Limni Aegean). Our results reveal Mediterranean forcing across Heinrich Stadial 4 (40.2–38.3 BP), period known climatic change. We identify decline tree all likely related onset enhanced regional aridity, at responding prior CI/Y-5, contrast Ioannina, where much occurs following deposition.

Language: Английский

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Multiple thermal Atlantic Meridional Overturning Circulation thresholds in the intermediate complexity model Bern3D

Climate of the past, Journal Year: 2024, Volume and Issue: 20(6), P. 1233 - 1250

Published: June 3, 2024

Abstract. Variations in the Atlantic Meridional Overturning Circulation (AMOC) are associated with Northern Hemispheric and global climate shifts. Thermal thresholds of AMOC have been found a hierarchy numerical circulation models, there is an increasing body evidence for existence highly sensitive modes where small perturbations can cause disproportionately large hence climatic changes. We discovered such simulations intermediate-complexity Earth system model Bern3D, which computationally efficient, allowing studying this non-linear behaviour systematically over entire glacial cycles. By simulating under different magnitudes orbitally paced changes radiative forcing last 788 000 years, we show that up to three thermal crossed during cycles Bern3D could destabilised repeatedly. present sea ice patterns characterise stable between oscillates cycle assess how often when preconditioned abrupt shifts kyr.

Language: Английский

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Simulated millennial-scale climate variability driven by a convection–advection oscillator

Climate Dynamics, Journal Year: 2025, Volume and Issue: 63(3)

Published: March 1, 2025

The last glacial period, between around 115 and 12 thousand years before present, exhibited strong millennial-scale climate variability. This includes abrupt transitions cold warm climates, known as Dansgaard-Oeschger (D-O) cycles. D-O cycles have been linked to switches in dynamical regimes of the Atlantic Overturning Meridional Circulation (AMOC), but exact mechanisms behind changes AMOC regime shifts remain poorly understood. paper introduces convection-advection oscillator mechanism explain oscillations observed a set HadCM3 general circulation model simulations forced with snapshots deglacial meltwater history. can be separated into two components acting on different time scales. fast convection component responds vertical stratification North by activating or deactivating deep water formation sites. slow advection regulates accumulation depletion salinity Atlantic. is triggered under specific background conditions freshwater release patterns. perturbation causes an instability that triggers global salt reorganisation, modifying stratification. For given forcing pattern, system oscillates if transport lead alternating reactivation deactivation AMOC. Otherwise, settles steady state. expands existing theories variability provides framework for understanding change models. online version contains supplementary material available at 10.1007/s00382-025-07630-x.

Language: Английский

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