Regional temperature extremes and vulnerability under net zero CO<sub>2</sub> emissions

Cassidy, Liam J; King, Andrew D; Brown, Josephine R; MacDougall, Andrew H; Ziehn, Tilo; Min, Seung-Ki; Jones, Chris D

doi:10.1088/1748-9326/ad114a

Cited by 3 publications

(1 citation statement)

References 37 publications

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“…Previous studies have shown that under net negative emissions scenarios, there are substantial regional differences in projections of temperature change following cessation of CO 2 emissions (e.g. MacDougall et al 2022); for example, while landmasses are generally projected to cool, warming continues in the Southern Ocean (Cassidy et al 2023), with ramifications such as ongoing Antarctic sea ice decline (Chamberlain et al 2023). Under a socioeconomic pathway of continued fossil fuel-driven development, rising CO 2 concentrations persist beyond 2200, with scenario extensions thus enabling investigation of the long-term climate implications of continuously increasing levels of radiative forcing.…”

Section: Introductionmentioning

confidence: 99%

Global-scale future climate projections from ACCESS model contributions to CMIP6

Schroeter,

Bi,

Law

et al. 2024

J. South. Hemisph. Earth Syst. Sci.

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This paper describes projected climate evolution and outcomes simulated by the Australian Community Climate and Earth System Simulator (ACCESS) to varying future scenarios, including of socio-ecological and technological development, and land-use and land-cover change. Contributions to the Coupled Model Intercomparison Project Phase 6 (CMIP6) from the climate model version, ACCESS-CM2, and the fully coupled Earth System Model version, ACCESS-ESM1.5, are presented for the near-future (2020–2050), 21st Century (2000–2100) and longer-term (2100–2300). Scenario differentiation in the near future is aided by high-density sampling in large-ensemble ACCESS-ESM1.5, more clearly illustrating projected 2020–2050 global changes in temperature, precipitation and aerosol optical depth. Over the 21st Century, the heightened equilibrium climate sensitivity of ACCESS-CM2 relative to ACCESS-ESM1.5 results in persistently greater surface air temperature increases and larger amplified polar warming, leading to more rapid sea ice decline. Although weakening of the Atlantic meridional overturning circulation (AMOC) occurs in both models, 21st Century recovery under aggressive-mitigation and overshoot scenarios only occurs in ACCESS-ESM1.5; AMOC weakening continues under all scenarios in ACCESS-CM2 through to 2100. Longer-term climate response from simulations extending to 2300 depict opposing hemispheric responses of polar surface air temperatures and sea ice in both models under scenarios based on aggressive mitigation action, leading to a resurgence of surface ocean warming and Antarctic sea ice decline. Under a future scenario where development is driven by continued fossil fuel use, both AMOC and Antarctic Bottom Water Formation continue to weaken across 2200–2300 in both models, reaching such low levels in ACCESS-CM2 that these pivotal components of global meridional overturning circulation could be considered essentially to have ceased.

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Section: Introductionmentioning

confidence: 99%

Global-scale future climate projections from ACCESS model contributions to CMIP6

Schroeter,

Bi,

Law

et al. 2024

J. South. Hemisph. Earth Syst. Sci.

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The Southern Ocean as the climate's freight train – driving ongoing global warming under zero-emission scenarios with ACCESS-ESM1.5

Chamberlain,

Ziehn,

Law

2024

Biogeosciences

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Abstract. Earth system model experiments presented here explore how the centennial response in the Southern Ocean can drive ongoing global warming even with zero CO2 emissions and declining atmospheric CO2 concentrations. These projections were simulated by the earth system model version of the Australian Community Climate and Earth System Simulator (ACCESS-ESM1.5) and motivated by the Zero Emissions Commitment Model Intercomparison Project (ZECMIP); ACCESS-ESM1.5 simulated ongoing warming in the ZECMIP experiment that switched or branched to zero emissions after 2000 PgC had been emitted. New experiments presented here each simulated 300 years and included intermediate branch points. In each experiment that branched after emitting more than 1000 PgC, the global climate continues to warm. For the experiment that branched after 2000 PgC, or after 3.5 °C of warming from a preindustrial climate, there is 0.37 ± 0.08 °C of extra warming after 50 years of zero emissions, which increases to 0.83 ± 0.08 °C after 200 years. All branches show ongoing Southern Ocean warming. The circulation of the Southern Ocean is modified early in the warming climate, which contributes to changes in the distribution of both physical and biogeochemical subsurface ocean tracers, such as ongoing warming at intermediate depths and a reduction in deep oxygen south of 60° S. A simple slab model emulates the global temperatures of the ACCESS-ESM1.5 experiments demonstrating the response here is primarily due to the slow response of the ocean and the Southern Ocean in particular. Centennial global warming persists when the slab model is forced with CO2 diagnosed from late-branching experiments with other ZECMIP models, confirming the dominant role of ocean physics at these timescales. However, decadal responses changed due to the larger drawdown of CO2 from other models. Slow ongoing warming in the Southern Ocean can be found in ZEC scenarios of most models, though the amplitude and global influence varies.

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Exploring climate stabilisation at different global warming levels in ACCESS-ESM-1.5

King,

Ziehn,

Chamberlain

et al. 2024

Earth Syst. Dynam.

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Abstract. Under the Paris Agreement, signatory nations aim to keep global warming well below 2 °C above pre-industrial levels and preferably below 1.5 °C. This implicitly requires achieving net-zero or net-negative greenhouse gas emissions to ensure long-term global temperature stabilisation or reduction. Despite this requirement, there have been few analyses of stabilised climates, and there is a lack of model experiments to address our need for understanding the implications of the Paris Agreement. Here, we describe a new set of experiments using the Australian Community Climate and Earth System Simulator Earth system model (ACCESS-ESM-1.5) that enables the analysis of climate evolution under net-zero emissions, and we present initial results. Seven 1000-year-long simulations were run with global temperatures stabilising at levels in line with the Paris Agreement and at a range of higher global warming levels (GWLs). We provide an overview of the experimental design and use these simulations to demonstrate the consequences of delayed attainment of global net-zero carbon dioxide emissions. We show that there are substantial differences between transient and stabilising climate states and differences in stabilisation between GWLs. As the climate stabilises under net-zero emissions, we identify significant and robust changes in temperature and precipitation patterns including continued Southern Ocean warming and changes in regional precipitation trends. Changes under net-zero emissions differ greatly between regions, including contrasting trajectories of sea ice extent between the Arctic and Antarctic. We also examine the El Niño–Southern Oscillation (ENSO) and find evidence of reduced amplitude and frequency of ENSO events under climate stabilisation relative to projections under transient warming. An analysis at specific GWLs shows that significant regional changes continue for centuries after emission cessation and that these changes are stronger at higher GWLs. Our findings suggest substantial long-term climate changes are possible even under net-zero emission pathways. These simulations are available for use in the community and will hopefully motivate further experiments and analyses based on other Earth system models.

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Regional temperature extremes and vulnerability under net zero CO₂ emissions

Cited by 3 publications

References 37 publications

Global-scale future climate projections from ACCESS model contributions to CMIP6

Global-scale future climate projections from ACCESS model contributions to CMIP6

The Southern Ocean as the climate's freight train – driving ongoing global warming under zero-emission scenarios with ACCESS-ESM1.5

Exploring climate stabilisation at different global warming levels in ACCESS-ESM-1.5

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Regional temperature extremes and vulnerability under net zero CO2 emissions

Cited by 3 publications

References 37 publications

Global-scale future climate projections from ACCESS model contributions to CMIP6

Global-scale future climate projections from ACCESS model contributions to CMIP6

The Southern Ocean as the climate's freight train – driving ongoing global warming under zero-emission scenarios with ACCESS-ESM1.5

Exploring climate stabilisation at different global warming levels in ACCESS-ESM-1.5

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Regional temperature extremes and vulnerability under net zero CO₂ emissions