Extreme precipitation (EP) in the Northeastern United States increased abruptly after 1996, coinciding with warming Atlantic sea surface temperatures (SSTs). We examine the importance of internal variability and external forcings (including anthropogenic and natural forcings) to these EP and SST increases by using the Community Earth System Model large ensembles and an optimal fingerprint method to isolate the effects of different forcings on 1929–2018 Northeast EP and North Atlantic SSTs. We find that external forcings have significantly influenced both Northeast EP and North Atlantic SSTs, with a time of detection in 2008 and 1968, respectively. Beyond SST changes attributable to internal variability of the Atlantic, anthropogenic aerosols and greenhouse gases are important drivers of SST changes, first detected in 1968 and 1983, respectively. Greenhouse gases are the only anthropogenic forcing exerting substantial influence on EP, first detected in 2008. We therefore attribute the 1996 EP shift to both unforced Atlantic variability and anthropogenic forcings.

美国东北部的极端降水 (EP) 在 1996 年之后突然增加，与大西洋海面温度 (SST) 变暖相吻合。我们通过使用社区地球系统模型大型集合和最佳指纹方法来隔离不同强迫对 1929-2018 东北 EP 的影响，研究内部变异和外部强迫（包括人为和自然强迫）对这些 EP 和 SST 增加的重要性和北大西洋 SST。我们发现外部强迫对东北 EP 和北大西洋海温都有显着影响，检测时间分别为 2008 年和 1968 年。除了归因于大西洋内部变异的 SST 变化之外，人为气溶胶和温室气体是 SST 变化的重要驱动因素，分别于 1968 年和 1983 年首次发现。