King et al. (2025) ESD Ideas: Extended net zero simulations are critical for informed decision making

Identification

• Journal: Earth System Dynamics
• Year: 2025
• Date: 2025-10-08
• Authors: Andrew D. King, Nerilie J. Abram, Eduardo Alastrué de Asenjo, Tilo Ziehn
• DOI: 10.5194/esd-16-1605-2025

Research Groups

• ARC Centre of Excellence for the Weather of the 21st Century, Melbourne, Kulin nations, Australia
• School of Geography, Earth and Atmospheric Sciences, University of Melbourne, Melbourne, Kulin nations, Australia
• Research School of Earth Sciences, The Australian National University, Ngunnawal country, Canberra ACT 2601, Australia
• Institute of Oceanography, Center for Earth System Research and Sustainability (CEN), University of Hamburg, Hamburg, Germany
• Max Planck Institute for Meteorology, Hamburg, Germany
• CSIRO Environment, Aspendale, Kulin nations, Australia

Short Summary

This paper argues that extended, millennial-length Earth System Model simulations of net zero emissions are crucial for understanding long-term committed climate changes, particularly regional extremes and the impact of delayed emissions cessation, to inform robust policymaking.

Objective

• To advocate for the necessity of extended, multi-model Earth System Model simulations (millennial length) under net zero emissions to better quantify long-term, regional climate changes and extremes, and the consequences of delays in achieving net zero.

Study Configuration

• Spatial Scale: Global, regional (e.g., Southern Hemisphere, Southern Ocean, Australia, Europe), and local.
• Temporal Scale: Centuries to millennia (specifically advocating for 1000-year simulations, contrasting with typical 300-year simulations).

Methodology and Data

• Models used: The paper advocates for the use of Earth System Models (ESMs) and refers to previous work utilizing ACCESS-ESM-1.5 and CanESM2. It also discusses Earth System Models of Intermediate Complexity (EMICs) in the context of past studies and their limitations. It proposes extensions to simulations within the flat10MIP and TipMIP frameworks.
• Data sources: Primarily refers to outputs from Earth System Model simulations, including those from ZECMIP, flat10MIP, and TipMIP. Specific data from ACCESS-ESM-1.5 experiments (King, 2024) is referenced.

Main Results

• Climate changes, particularly in the ocean and cryosphere, will continue for many centuries after net zero emissions are achieved, leading to significant regional and local impacts.
• Current net zero emissions simulations, often limited to approximately 300 years, are insufficient to capture these long-term changes, especially concerning regional extremes and climate variability.
• Delays in achieving net zero emissions by even a few decades can result in substantially different magnitudes of long-term climate commitments.
• A critical knowledge gap exists in understanding long-term changes under net zero, particularly for local changes, extremes, and the potential for climate tipping points.
• The paper recommends that modeling centers run two 1000-year-long ESM simulations as extensions of existing plans, either at 1000 and 1500 PgC cumulative emissions levels (flat10MIP framework) or at 2 °C and 4 °C global warming levels (TipMIP framework).
• Such extended simulations are essential for quantifying the long-term effect of delays in achieving net zero, identifying model response differences for uncertain changes, robustly quantifying mean and extreme climate changes, identifying potential tipping points, and analyzing changes in climate variability (e.g., ENSO, AMOC).

Contributions

• Identifies and highlights a critical knowledge gap regarding the understanding of long-term (millennial-scale) regional and local climate changes and extremes under net zero emissions, attributing it to the insufficient length of current Earth System Model simulations.
• Proposes a concrete and actionable recommendation for specific extended Earth System Model simulations (1000-year length at defined cumulative emissions or global warming levels) to address this gap.
• Emphasizes the direct policy relevance of these extended simulations for informed decision-making, particularly concerning the long-term impacts of delayed emissions cessation and regional adaptation strategies.

Funding

• Australian Research Council (grant nos. CE230100012, FT240100306, SR200100008)
• Australian Government National Environmental Science Program
• Deutsche Forschungsgemeinschaft (DFG) under Germany’s Excellence Strategy – EXC 2037 “CLICCS – Climate, Climatic Change, and Society” (Project Number: 390683824)

Citation

@article{King2025ESD,
  author = {King, Andrew D. and Abram, Nerilie J. and Asenjo, Eduardo Alastrué de and Ziehn, Tilo},
  title = {ESD Ideas: Extended net zero simulations are critical for informed decision making},
  journal = {Earth System Dynamics},
  year = {2025},
  doi = {10.5194/esd-16-1605-2025},
  url = {https://doi.org/10.5194/esd-16-1605-2025}
}