Meteorological Research Institute, Japan Meteorological Agency, Tsukuba 305-0052, Japan.
Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, Yokohama 236-0001, Japan.
Proc Natl Acad Sci U S A. 2022 Jul 19;119(29):e2200635119. doi: 10.1073/pnas.2200635119. Epub 2022 Jul 11.
How subtropical marine low cloud cover (LCC) will respond to global warming is a major source of uncertainty in future climate change. Although the estimated inversion strength (EIS) is a good predictive index of LCC, it has a serious limitation when applied to evaluate LCC changes due to warming: The LCC decreases despite increases in EIS in future climate simulations of global climate models (GCMs). In this work, using state-of-the-art GCMs, we show that the recently proposed estimated cloud-top entrainment index (ECTEI) decreases consistently with LCC in warmer sea surface temperature (SST) climates. For the patterned SST warming predicted by coupled GCMs, ECTEI can constrain the subtropical marine LCC feedback to -0.41 ± 0.28% K (90% CI), implying virtually certain positive feedback. ECTEI physically explains the heuristic model for LCC changes based on a linear combination of EIS and SST changes in previous studies in terms of cloud-top entrainment processes.
亚热带海洋低云覆盖（LCC）将如何应对全球变暖是未来气候变化的主要不确定因素之一。尽管估计的反转强度（EIS）是 LCC 的良好预测指标，但在评估由于变暖导致的 LCC 变化时，它存在严重的局限性：在全球气候模型（GCM）的未来气候模拟中，尽管 EIS 增加，但 LCC 却减少了。在这项工作中，我们使用最先进的 GCM 表明，最近提出的估计云顶夹带指数（ECTEI）在温暖的海表温度（SST）气候下与 LCC 一致下降。对于耦合 GCM 预测的模式化 SST 变暖，ECTEI 可以将亚热带海洋 LCC 反馈约束为-0.41±0.28% K（90%CI），这意味着实际上存在正反馈。ECTEI 从物理上解释了基于先前研究中 EIS 和 SST 变化的线性组合的启发式 LCC 变化模型，根据云顶夹带过程。
