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

• Published in: Biogeosciences Vol. 21; no. 12; pp. 3053 - 3073
• Main Authors: Chamberlain, Matthew A, Ziehn, Tilo, Law, Rachel M
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau Copernicus GmbH 01.07.2024; Copernicus Publications
• Subjects: Air pollution; Analysis; Biogeochemistry; Carbon; Carbon cycle; Carbon dioxide; Climate; Climate change; Cooling; Drawdown; Earth; Emissions; Environmental aspects; Experiments; Freight trains; Global climate; Global temperatures; Global warming; Intercomparison; Ocean circulation; Ocean temperature; Ocean warming; Oceans; Physics; Simulation; Simulators; Temperature; Time series; Tracers; Trends; Southern Ocean
• ISSN: 1726-4189; 1726-4170; 1726-4189
• DOI: 10.5194/bg-21-3053-2024

Earth system model experiments presented here explore how the centennial response in the Southern Ocean can drive ongoing global warming even with zero CO.sub.2 emissions and declining atmospheric CO.sub.2 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.