Asymmetrical response of summer rainfall in East Asia to CO2 forcing

• Published in: Science bulletin (Beijing) 2022-01, Vol.67 (2), p.213-222
• Main Authors: Song, Se-Yong, Yeh, Sang-Wook, An, Soon-Il, Kug, Jong-Seong, Min, Seung-Ki, Son, Seok-Woo, Shin, Jongsoo
• Format: Article
• Language: English
• Subjects: Asymmetric rainfall; CO2 concentration; East Asian summer monsoon; El Niño-like warming
• ISSN: 2095-9273
• DOI: 10.1016/j.scib.2021.08.013

Summer monsoon rainfall in East Asia gradually strengthens in response to CO2 increase (ramp-up period), but this reverses slowly following CO2 decrease (ramp-down period), showing an asymmetric behavior in a changing CO2 pathway. [Display omitted] 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.