Understanding the regional hydrological response to varying CO₂ concentration is critical for cost-benefit analysis of mitigation and adaptation polices in the near future. To characterize summer monsoon rainfall change in East Asia in a changing CO₂ pathway, we used the Community Earth System Model (CESM) with 28 ensemble members in which the CO₂ concentration increases at a rate of 1% per year until its quadrupling peak, i.e., 1468 ppm (ramp-up period), followed by a decrease of 1% per year until the present-day climate conditions, i.e., 367 ppm (ramp-down period). Although the CO₂ concentration change is symmetric in time, the amount of summer rainfall anomaly in East Asia is increased 42% during a ramp-down period than that during a ramp-up period when the two periods of the same CO₂ concentration are compared. This asymmetrical rainfall response is mainly due to an enhanced El Niño-like warming pattern as well as its associated increase in the sea surface temperature in the western North Pacific during a ramp-down period. These sea surface temperature patterns enhance the atmospheric teleconnections and the local meridional circulations around East Asia, resulting in more rainfall over East Asia during a ramp-down period. This result implies that the removal of CO₂ does not guarantee the return of regional rainfall to the previous climate state with the same CO₂ concentration.

了解区域水文对不同 CO ₂浓度的响应对于近期缓解和适应政策的成本效益分析至关重要。_{为了在不断变化的 CO 2}路径中描述东亚夏季风降雨变化的特征，我们使用了社区地球系统模型 (CESM) 和 28 个合奏成员，其中 CO ₂浓度以每年 1% 的速度增加，直到其四倍峰值，即 1468 ppm（上升期），然后每年减少 1%，直到当今的气候条件，即 367 ppm（下降期）。虽然CO _{2浓度变化在时间上是对称的，当CO 2}浓度相同的两个时期比较时，东亚夏季降水量异常在斜降期比斜升期增加了42% 。这种不对称的降雨反应主要是由于类似厄尔尼诺现象的变暖模式增强以及与之相关的北太平洋西部海面温度在下降期间的上升。这些海面温度模式增强了大气遥相关和东亚周围的局部经向环流，导致在斜坡下降期间东亚降雨量增加。这一结果意味着去除 CO ₂不保证区域降雨量恢复到先前具有相同 CO ₂浓度的气候状态。