The effective climate sensitivity estimates the equilibrium response of near-surface temperature to doubling atmospheric carbon dioxide concentration and is a widely used metric to characterize potential global warming. Earth system models participating in phase 6 of the Coupled Model Intercomparison Project (CMIP6) exhibit considerable spread in effective climate sensitivity estimates. Cloud feedbacks are thought to be the cause of this, with marine boundary layer clouds over the Southern Ocean playing an important role. Here, we show that Southern Ocean deep convection is a major contributor to the CMIP6 intermodel spread in effective climate sensitivity. By comparing two Earth system models with very different sensitivities, we find that greater storage of heat at depth can delay the Southern Ocean surface warming and associated cloud response, thereby delaying global surface warming by centuries. The link between Southern Ocean convection and effective climate sensitivity is seen across 41 CMIP6 models, with low-sensitivity models exhibiting substantial deep ocean warming. Our results reveal the influence of Southern Ocean convection on potential long-term climate warming.

有效气候敏感性估计近地表温度对大气二氧化碳浓度加倍的平衡响应，是一种广泛使用的衡量潜在全球变暖的指标。参与耦合模式比对项目 (CMIP6) 第 6 阶段的地球系统模式在有效气候敏感性估计方面表现出相当大的分布。云反馈被认为是造成这种情况的原因，南大洋上空的海洋边界层云起着重要作用。在这里，我们表明南大洋深层对流是有效气候敏感性中 CMIP6 模式间传播的主要贡献者。通过比较具有非常不同灵敏度的两个地球系统模型，我们发现在深处储存更多的热量可以延迟南大洋表面变暖和相关的云响应，从而将全球地表变暖延迟了几个世纪。在 41 个 CMIP6 模型中可以看到南大洋对流与有效气候敏感性之间的联系，其中低敏感性模型表现出大量的深海变暖。我们的结果揭示了南大洋对流对潜在的长期气候变暖的影响。