It remains unresolved whether the La Niña-like sea surface temperature (SST) trend pattern during the satellite era, featuring a distinct warming in the northwest/southwest Pacific but cooling in the tropical eastern Pacific, is driven by either external forcing or internal variability. Here, by conducting a comprehensive analysis of observations and a series of climate model simulations for the historical period, we show that a combination of internal variability and human activity may have shaped the observed La Niña-like SST trend pattern. As in observations, SSTs in each model ensemble member show a distinct multi-decadal swing between El Niño-like and La Niña-like trend patterns due to internal variability. The ensemble-mean trends for some models are, however, found to exhibit an enhanced zonal SST gradient along the equatorial Pacific over periods such as 1979–2010, suggesting a role of external forcing. In line with this hypothesis, single-forcing large ensemble model simulations show that human-induced stratospheric ozone depletion and/or aerosol changes have acted to enhance the zonal SST gradient via strengthening of Pacific trade winds, although the effect is model dependent. Our finding suggests that the La Niña-like SST trend is unlikely to persist under sustained global warming because both the ozone and aerosol impacts will eventually weaken.

卫星时代的类拉尼娜海面温度（SST）趋势模式（西北/西南太平洋明显变暖，但热带东太平洋明显变冷）是否是由外部强迫或内部变率驱动的，目前尚无定论。在这里，通过对历史时期的观测和一系列气候模型模拟进行综合分析，我们表明内部变率和人类活动的结合可能塑造了观测到的类拉尼娜海温趋势模式。正如观测结果所示，由于内部变异性，每个模式集合成员的海温在类厄尔尼诺和类拉尼娜趋势模式之间显示出明显的数十年摆动。然而，一些模型的集合平均趋势被发现在 1979 年至 2010 年等时期沿赤道太平洋呈现出增强的纬向海温梯度，这表明存在外部强迫的作用。根据这一假设，单强迫大型集合模型模拟表明，人为引起的平流层臭氧消耗和/或气溶胶变化通过太平洋信风的加强增强了纬向海温梯度，尽管这种影响取决于模型。我们的研究结果表明，在全球持续变暖的情况下，类似拉尼娜现象的海温趋势不太可能持续下去，因为臭氧和气溶胶的影响最终都会减弱。