All climate models project a weakening of the Atlantic Meridional Overturning Circulation (AMOC) strength in response to greenhouse gas forcing. However, the climate impacts of the AMOC decline alone cannot be isolated from other drivers of climate change using existing Coupled Model Intercomparison Project simulations. To address this issue, we conduct idealized experiments using the EC-Earth3 climate model. We compare an abrupt 4×CO₂ simulation with the same experiment, except we artificially fix the AMOC strength at preindustrial levels. With this design, we can formally attribute differences in climate change impacts between these two experiments to the AMOC decline. In addition, we quantify the state-dependence of AMOC impacts by comparing the aforementioned experiments with a preindustrial simulation in which we artificially reduce the AMOC strength. Our findings demonstrate that AMOC decline impacts are state-dependent, thus understanding AMOC impacts on future climate change requires targeted model experiments.

中文翻译：

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气候变暖时 AMOC 减弱的影响和国家依赖性

所有气候模型都预测大西洋经向翻转环流（AMOC）强度会因温室气体强迫而减弱。然而，使用现有的耦合模型比对项目模拟，无法将 AMOC 下降的气候影响与气候变化的其他驱动因素分开。为了解决这个问题，我们使用 EC-Earth3 气候模型进行了理想化实验。我们将突然的 4×CO ₂模拟与相同的实验进行比较，只是我们人为地将 AMOC 强度固定在工业化前的水平。通过这种设计，我们可以将这两个实验之间气候变化影响的差异正式归因于 AMOC 的下降。此外，我们通过将上述实验与工业化前的模拟进行比较（在模拟中人为降低 AMOC 强度）来量化 AMOC 影响的状态依赖性。我们的研究结果表明，AMOC 下降的影响取决于国家，因此了解 AMOC 对未来气候变化的影响需要有针对性的模型实验。