A variety of hypotheses, involving sub-ice-shelf melting, stratospheric ozone depletion and tropical teleconnections, have been proposed to explain the observed Antarctic sea-ice expansion over the period of continuous satellite monitoring and corresponding model–observation discrepancy, but the issue remains unresolved. Here, by comparing multiple large ensembles of model simulations with available observations, we show that Antarctic sea ice has expanded due to ocean surface cooling associated with multidecadal variability in the Southern Ocean that temporarily outweighs the opposing forced response. In both observations and model simulations, Southern Ocean multidecadal variability is closely linked to internal variability in the tropics, especially in the Pacific, via atmospheric teleconnections. The linkages are, however, distinctly weaker in simulations than in observations, accompanied by a marked model–observation mismatch in global warming resulting from potential model bias in the forced response and observed tropical variability. Thus, the forced response dominates in simulations, resulting in apparent model–observation discrepancy.

已经提出了各种假设，包括冰架下融化、平流层臭氧消耗和热带遥相关，以解释在连续卫星监测期间观测到的南极海冰膨胀和相应的模型观测差异，但问题仍然存在未解决。在这里，通过将多个大型模型模拟集合与可用观测结果进行比较，我们表明南极海冰已经扩大，原因是海洋表面冷却与南大洋的多年代际变率相关，暂时超过了相反的强制响应。在观测和模型模拟中，南大洋的多年代际变率通过大气遥相关与热带地区，特别是太平洋的内部变率密切相关。然而，这些联系是 模拟明显弱于观测，伴随着全球变暖的显着模型 - 观测不匹配，这是由于强迫响应中的潜在模型偏差和观察到的热带变化造成的。因此，强制响应在模拟中占主导地位，导致明显的模型观察差异。