Asymmetry of AMOC Hysteresis in a State‐Of‐The‐Art Global Climate Model

van Westen, René M.; Dijkstra, Henk A.

doi:10.1029/2023gl106088

Geophysical Research Letters

2023

DOI: 10.1029/2023gl106088

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Asymmetry of AMOC Hysteresis in a State‐Of‐The‐Art Global Climate Model

René M. van Westen,

Henk A. Dijkstra

Abstract: We study hysteresis properties of the Atlantic Meridional Overturning Circulation (AMOC) under a slowly‐varying North Atlantic (20°N–50°N) freshwater flux forcing in state‐of‐the‐art global climate model (GCM), the Community Earth System Model. Results are presented of a full hysteresis simulation (4,400 model years) and show that there is a hysteresis width of about 0.4 Sv. This demonstrates that an AMOC collapse and recovery do not only occur in conceptual and idealized climate models, but also in a state‐of… Show more

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2024

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Cited by 9 publications

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Tipping mechanisms in a conceptual model of the Atlantic Meridional Overturning Circulation

Chapman,

Sinet,

Ritchie

2024

Weather

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The Atlantic Meridional Overturning Circulation (AMOC) forms an essential component of the global ocean circulation. Paleoclimate records indicate the AMOC’s capability to tip between different states that resulted in large global climate impacts. Using an AMOC box model, re‐calibrated against a global circulation model, HadGEM3, we present a new bifurcation analysis and showcase mechanisms that may lead the AMOC to tip from its current ‘on’ state to a collapsed ‘off’ state under climate change. We find that bifurcation‐ and noise‐induced tipping remain viable tipping mechanisms as in previous calibrations, while rate‐induced tipping only occurs for specific parameter configurations of this model.

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Tipping mechanisms in a conceptual model of the Atlantic Meridional Overturning Circulation

Chapman,

Sinet,

Ritchie

2024

Weather

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Persistently Elevated High‐Latitude Ocean Temperatures and Global Sea Level Following Temporary Temperature Overshoots

Lacroix,

Burger,

Silvy

et al. 2024

Earth's Future

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As exceeding the 1.5°C level of global warming is likely to happen in the near future, understanding the response of the ocean‐climate system to temporarily overshooting this warming level is of critical importance. Here, we apply the Adaptive Emissions Reduction Approach to the Earth System Model GFDL‐ESM2M to conduct novel overshoot scenarios that reach 2.0, 2.5 and 3.0°C of global warming before returning to 1.5°C over the time period of 1861–2500. We also perform a complementary scenario that stabilizes global temperature at 1.5°C, allowing to isolate impacts caused by the temperature overshoots alone, both during their peaks and after their reversals. The simulations indicate that substantial residual ocean surface warming persists in the high latitudes after the overshoots, with most notable regional anomalies occurring in the North Atlantic (up to +3.1°C in the 3°C overshoot scenario compared to the 1.5°C stabilization scenario) and the Southern Ocean (+1.2°C). The residual warming is primarily driven by the recoveries of the Atlantic and Southern Ocean meridional overturning circulation and associated increases in ocean heat transport. Excess subsurface heat storage in low and mid‐latitudes prevents steric sea level rise (SLR) from reverting to 1.5°C stabilization levels in any overshoot scenario, with steric sea level remaining up to 32% higher in the 3°C overshoot scenario on centennial time scales. Both peak impacts and persistent changes after overshoot reversal bear significant implications for future assessments of coastlines, regional climates, marine ecosystems, and ice sheets.

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Centennial‐Scale Variability of the Atlantic Meridional Overturning Circulation in CMIP6 Models Shaped by Arctic–North Atlantic Interactions and Sea Ice Biases

Mehling,

Bellomo,

von Hardenberg

2024

Geophysical Research Letters

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Climate variability on centennial timescales has often been linked to internal variability of the Atlantic Meridional Overturning Circulation (AMOC). However, due to the scarceness of suitable paleoclimate proxies and long climate model simulations, large uncertainties remain on the magnitude and physical mechanisms driving centennial‐scale AMOC variability. For these reasons, we perform a systematic multi‐model comparison of centennial‐scale AMOC variability in pre‐industrial control simulations of state‐of‐the‐art global climate models. Six out of nine models in this study exhibit a statistically significant mode of centennial‐scale AMOC variability. Our results show that freshwater exchanges between the Arctic Ocean and the North Atlantic provide a plausible driving mechanism in a subset of models, and that AMOC variability can be amplified by ocean–sea ice feedbacks in the Labrador Sea. The amplifying mechanism is linked to sea ice cover biases, which could provide an observational constraint for centennial‐scale AMOC variability.

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Asymmetry of AMOC Hysteresis in a State‐Of‐The‐Art Global Climate Model

Cited by 9 publications

References 47 publications

Tipping mechanisms in a conceptual model of the Atlantic Meridional Overturning Circulation

Tipping mechanisms in a conceptual model of the Atlantic Meridional Overturning Circulation

Persistently Elevated High‐Latitude Ocean Temperatures and Global Sea Level Following Temporary Temperature Overshoots

Centennial‐Scale Variability of the Atlantic Meridional Overturning Circulation in CMIP6 Models Shaped by Arctic–North Atlantic Interactions and Sea Ice Biases

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