The role of the Southern Ocean in the global climate response to carbon emissions

Abstract

The effect of the Southern Ocean on global climate change is assessed using Earth system model projections following an idealized 1% annual rise in atmospheric CO 2 . For this scenario, the Southern Ocean plays a significant role in sequestering heat and anthropogenic carbon, accounting for 40% ± 5% of heat uptake and 44% ± 2% of anthropogenic carbon uptake over the global ocean (with the Southern Ocean defined as south of 36°S). This Southern Ocean fraction of global heat uptake is however less than in historical scenarios with marked hemispheric contrasts in radiative forcing. For this idealized scenario, inter-model differences in global and Southern Ocean heat uptake are strongly affected by physical feedbacks, especially cloud feedbacks over the globe and surface albedo feedbacks from sea-ice loss in high latitudes, through the top-of-the-atmosphere energy balance. The ocean carbon response is similar in most models with carbon storage increasing from rising atmospheric CO 2 , but weakly decreasing from climate change with competing ventilation and biological contributions over the Southern Ocean. The Southern Ocean affects a global climate metric, the transient climate response to emissions, accounting for 28% of its thermal contribution through its physical climate feedbacks and heat uptake, and so affects inter-model differences in meeting warming targets. This article is part of a discussion meeting issue 'Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities'.

Reply on RC1

“…The subpolar North Atlantic north of 40ºN (and using the northern boundary of Fay and McKinley (2014)) represents 3 % of the ocean area, but takes up 7 % (3 % to 11 %) of global ocean carbon uptake by 2020, a fraction that decreases to 5 % (1 % to 11 %) by 2150. The prevalence of the Southern Ocean carbon sink is consistent with results from CMIP5 and CMIP6 simulations for the historical period and for idealized 1pctCO 2 experiments Terhaar et al, 2021;Williams et al, 2023). The pronounced long-term steady carbon sink in the Southern Ocean can be attributed to the high carbon concentration feedback and efficient surface to deep export of anthropogenic carbon shown in earlier studies (Tjiputra et al, 2010;Roy et al, 2011).…”

Finale: impact of the ORCHESTRA/ENCORE programmes on Southern Ocean heat and carbon understanding

“…Williams et al . [ 85 ]). It also made significant contributions to parallel UK programmes working in the North Atlantic (e.g.…”

Surface Heat Fluxes Drive a Two‐Phase Response in Southern Ocean Mode Water Stratification

“…The Southern Ocean is globally important due to its role in the uptake and transport of heat and anthropogenic carbon (Frölicher et al., 2015; Williams et al., 2023). The Southern Ocean connects the three main ocean basins, Indian, Pacific, and Atlantic through the Antarctic Circumpolar Current (ACC).…”