Oh et al. (2025) Noise-induced tipping of Atlantic Meridional Overturning Circulation under climate mitigation scenarios

Identification

• Journal: Nature Communications
• Year: 2025
• Date: 2025-12-13
• Authors: Ji‐Hoon Oh, Jong‐Seong Kug, Yechul Shin, Xin Geng, Sunhee Wang, Fei‐Fei Jin, Soon‐Il An, Shang‐Ping Xie, Wei Liu
• DOI: 10.1038/s41467-025-66494-1

Research Groups

• Scripps Institution of Oceanography, University of California San Diego, USA
• School of Earth and Environmental Sciences, Seoul National University, South Korea
• CIC-FEMD, KLME, State Key Laboratory of Climate System Prediction and Risk Management, Nanjing University of Information Science and Technology, China
• Department of Atmospheric Sciences, University of Hawaii, USA
• Department of Atmospheric Sciences, Yonsei University, South Korea
• Department of Earth and Planetary Sciences, University of California Riverside, USA

Short Summary

This study investigates whether climate mitigation can prevent Atlantic Meridional Overturning Circulation (AMOC) collapse, revealing that even under CO2 stabilization, stochastic noise and delayed mitigation can trigger a multi-century AMOC collapse due to internal atmospheric variability near its stability threshold.

Objective

• To evaluate the effectiveness of climate mitigation efforts, initiated at different times, in preventing an Atlantic Meridional Overturning Circulation (AMOC) tipping point.

Study Configuration

• Spatial Scale: Global (Earth System Model), North Atlantic, subpolar North Atlantic, Labrador-Irminger Sea, Northern Hemisphere, Southern Hemisphere.
• Temporal Scale: Present-day control simulation (900 years), global warming simulation (140 years, 2001-2140), CO2 stabilization simulations (200 years), extended simulations (250 years, total 450 years), multi-century quasi-equilibrium states, CMIP6 model projections up to 2500.

Methodology and Data

• Models used: Community Earth System Model version 1 (CESM1), GISS-E2-1-G (CMIP6 model).
• Data sources: Ocean Reanalysis System 5 (ORAS5), Estimating the Circulation and Climate of the Ocean version 4 release 4 (ECCOv4r4), CMIP6 model output.

Main Results

• Under identical or comparable CO2 stabilization scenarios, AMOC evolution shows marked ensemble divergence, leading to either recovery (around 16 Sverdrups) or a multi-century collapsed state (around 3 Sverdrups).
• This divergence is attributed to the accumulation of stochastic noise near the AMOC stability threshold, driven by internal atmospheric variability characterized by persistent high-pressure anomalies over the subpolar North Atlantic.
• A modest delay in implementing climate mitigation significantly increases the likelihood of AMOC collapse.
• The AMOC stability indicator (ΔFov), representing basin-wide salt-advection feedback, consistently crosses zero in all ensemble members that experience AMOC collapse, confirming salt-advection feedback as the primary mechanism.
• Cumulative negative surface density flux, primarily thermal but also haline, over the Labrador-Irminger Sea, linked to reduced evaporation and an anomalous anticyclonic circulation, drives the AMOC towards collapse.
• AMOC tipping leads to strong cooling in the subpolar gyre region, extending across the Northern Hemisphere and to land areas in the Southern Hemisphere, alongside a reduction in Northern Hemisphere precipitation and a southward shift of the intertropical convergence zone.
• AMOC collapse significantly increases the irreversibility of regional sea level rise, particularly in the subpolar North Atlantic and Arctic regions.

Contributions

• Highlights that even under comparable CO2 forcing, noise-induced tipping of the AMOC can generate large and persistent spreads in regional climate outcomes, underscoring high uncertainties in future climate projections in response to mitigation efforts.
• Demonstrates that AMOC can collapse due to self-perpetuating salt-advection feedback even after CO2 stabilization, if the bifurcation tipping point is crossed, or due to stochastic noise before the bifurcation point.
• Emphasizes the critical importance of timely and robust climate mitigation actions (e.g., net-zero or negative CO2 emissions) to prevent AMOC collapse, especially given potential model biases that may underestimate the proximity of the real-world AMOC tipping point.

Funding

• National Research Foundation of Korea (NRF) (RS-2025-02653909, NRF-2022R1A3B1077622, RS-2024-00438471, RS-2024-00334637)
• Natural Science Foundation of Jiangsu Province (BK20251885)
• National Supercomputing Center (KSC-2025-CHA-0001)
• National Center for Meteorological Supercomputer of the Korea Meteorological Administration (KMA)
• Korea Research Environment Open NETwork (KREONET)

Citation

@article{Oh2025Noiseinduced,
  author = {Oh, Ji‐Hoon and Kug, Jong‐Seong and Shin, Yechul and Geng, Xin and Wang, Sunhee and Jin, Fei‐Fei and An, Soon‐Il and Xie, Shang‐Ping and Liu, Wei},
  title = {Noise-induced tipping of Atlantic Meridional Overturning Circulation under climate mitigation scenarios},
  journal = {Nature Communications},
  year = {2025},
  doi = {10.1038/s41467-025-66494-1},
  url = {https://doi.org/10.1038/s41467-025-66494-1}
}