Department of Meteorology, University of Reading, Reading RG6 6BB, United Kingdom;
Istituto di Scienze dell'Atmosfera e del Clima, Consiglio Nazionale delle Ricerche, Bologna 40129, Italy.
Proc Natl Acad Sci U S A. 2020 Mar 3;117(9):4539-4545. doi: 10.1073/pnas.1911015117. Epub 2020 Feb 18.
Greenhouse gas (GHG) emissions affect precipitation worldwide. The response is commonly described by two timescales linked to different processes: a rapid adjustment to radiative forcing, followed by a slower response to surface warming. However, additional timescales exist in the surface-warming response, tied to the time evolution of the sea-surface-temperature (SST) response. Here, we show that in climate model projections, the rapid adjustment and surface mean warming are insufficient to explain the time evolution of the hydro-climate response in three key Mediterranean-like areas-namely, California, Chile, and the Mediterranean. The time evolution of those responses critically depends on distinct shifts in the regional atmospheric circulation associated with the existence of distinct fast and slow SST warming patterns. As a result, Mediterranean and Chilean drying are in quasiequilibrium with GHG concentrations, meaning that the drying will not continue after GHG concentrations are stabilized, whereas California wetting will largely emerge only after GHG concentrations are stabilized. The rapid adjustment contributes to a reduction in precipitation, but has a limited impact on the balance between precipitation and evaporation. In these Mediterranean-like regions, future hydro-climate-related impacts will be substantially modulated by the time evolution of the pattern of SST warming that is realized in the real world.
温室气体（GHG）排放影响全球降水。这种响应通常由与不同过程相关的两个时间尺度来描述：对辐射强迫的快速调整，然后是对地表变暖的较慢响应。然而，在地表变暖响应中存在其他时间尺度，与海表温度（SST）响应的时间演化有关。在这里，我们表明，在气候模式预测中，快速调整和地表平均变暖不足以解释三个关键地中海类似地区——即加利福尼亚、智利和地中海——的水文气候响应的时间演化。这些响应的时间演化严重依赖于与不同的快速和缓慢 SST 变暖模式存在相关的区域大气环流的明显变化。结果，地中海和智利的干燥与温室气体浓度处于准平衡状态，这意味着在温室气体浓度稳定后，干燥不会持续，而加利福尼亚的湿润只有在温室气体浓度稳定后才会大量出现。快速调整有助于减少降水，但对降水和蒸发之间的平衡影响有限。在这些类似地中海的地区，未来与水文气候相关的影响将受到在现实世界中实现的 SST 变暖模式的时间演化的极大调节。
