Abstract. In 2020 the International Maritime Organization (IMO) implemented strict new regulations on the emissions of sulphate aerosol from the world's shipping fleet. This can be expected to lead to a reduction in aerosol-driven cooling, unmasking a portion of greenhouse gas warming. The magnitude of the effect is uncertain, however, due to the large remaining uncertainties in the climate response to aerosols. Here, we investigate this question using an 18-member ensemble of fully coupled climate simulations evenly sampling key modes of climate variability with the NCAR CESM2 model. We show that while there is a clear physical response of the climate system to the IMO regulations, including a surface temperature increase, we do not find global mean temperature influence that is significantly different from zero. The 20-year average global mean warming for 2020–2040 is +0.03 °C, with a 5–95 % confidence range of [-0.09, 0.19], reflecting the weakness of the perturbation relative to internal variability. We do, however, find a robust, non-zero regional temperature response in part of the North Atlantic. We also find that the maximum annual-mean ensemble-mean warming occurs around a decade after the perturbation in 2029, which means that the IMO regulations have likely had very limited influence on observed global warming to date. We further discuss our results in light of other, recent publications that have reached different conclusions. Overall, while the IMO regulations may contribute up to at 0.16 °C [-0.17, 0.52] to the global mean surface temperature in individual years during this decade, consistent with some early studies, such a response is unlikely to have been discernible above internal variability by the end of 2023 and is in fact consistent with zero throughout the 2020–2040 period.

中文翻译：

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最近航运二氧化硫排放量减少对表面温度的影响较弱，内部变化导致量化混乱


摘要。 2020 年，国际海事组织 (IMO) 对世界船队的硫酸盐气溶胶排放实施了严格的新规定。预计这将导致气溶胶驱动的冷却减少，从而揭示部分温室气体变暖的原因。然而，由于气候对气溶胶的反应仍然存在很大的不确定性，因此影响的程度尚不确定。在这里，我们使用由 18 个成员组成的完全耦合气候模拟集合来研究这个问题，通过 NCAR CESM2 模型对气候变化的关键模式进行均匀采样。我们表明，虽然气候系统对国际海事组织的规定有明显的物理反应，包括地表温度升高，但我们没有发现全球平均温度影响与零有显着不同。 2020年至2040年的20年平均全球变暖为+0.03°C，5%至95%的置信范围为[-0.09, 0.19]，反映出相对于内部变异性的扰动较弱。然而，我们确实在北大西洋部分地区发现了强劲的非零区域温度响应。我们还发现，年平均总体平均变暖幅度最大发生在 2029 年扰动之后的十年左右，这意味着 IMO 法规对迄今为止观测到的全球变暖的影响可能非常有限。我们根据其他最近得出不同结论的出版物进一步讨论我们的结果。总体而言，虽然 IMO 法规可能会导致 0.16 °C [-0.17, 0.52]根据这十年间个别年份的全球平均地表温度，与一些早期研究一致，到 2023 年底，这种响应不太可能在内部变化之上被辨别出来，实际上在 2020-2040 年期间与零一致时期。