[M-IS16] Paleoclimatology and paleoceanography

[MIS16-22] Opposing responses in the hydrological cycle of the East Asia to climate warming related with the Tibetan Plateau

*Taro Higuchi¹, Ayako Abe-Ouchi¹, Wing-Le Chan¹ (1.Atmospheric and Ocean Research Institute, the University of Tokyo)

Keywords:Hydrological cycle, East Asia, Global warming, Cretaceous, Tibetan plateau

The water cycle is closely linked to human lives, the ecosystem, ocean circulation and the carbon cycle, and its change due to increased atmospheric CO2 concentration is one of the major concerns in the field of global warming research. Numerical modelling studies using GCMs suggested that, in East Asia, the mean precipitation increases with future global warming, leading to more humid conditions. On the other hand, Cretaceous proxy data showed that aridification in the low latitudes of East Asia proceeded the mid-Cretaceous which was the warmest time during the Cretaceous Period, with an especially high CO2 concentration, compared to the relatively cold early and late Cretaceous. However, it remains unclear why the response of the water cycle in East Asia to increased CO2 differs during the present day and the Cretaceous and how the response in the Cretaceous compares with other periods. The aim of this study is to investigate the response of the climate and water cycle to increased atmospheric CO2 for a Cretaceous paleogeography and to compare results with the proxy data and warming experiments using the present-day, Pliocene, and Eocene conditions. In this study, simulations of the present-day, Pliocene, Eocene, and Cretaceous climate with different CO2 levels are carried out using the atmosphere-ocean general circulation model, MIROC4m. For all the experiments, the global hydrological sensitivity ranges from 1.98 to 2.14 %/K, which is fairly small. The "rich gets richer" mechanism can be seen zonally in all cases. On the other hand, there are two opposing responses in the local hydrological cycle in East Asia to climate warming. One response is that annual precipitation in East Asia increases as the climate warms, provided there is an elevated Tibetan Plateau (Present day, Pliocene), similar to global warming prediction. The other is that annual precipitation decreases without a Tibetan Plateau (Eocene, Cretaceous), consistent with the change in the hydrological cycle during the mid-Cretaceous as shown in proxy data. These opposing responses in the hydrological cycle may be attributed to the different basic climate fields and atmospheric circulation responses in Asia which, in turn, is associated with the presence or absence of the Tibetan Plateau. Furthermore, from the idealized sensitivity experiments of the Tibetan Plateau, it is found that the changes in the annual precipitation of East Asia due to increasing atmospheric CO2 are reversed by around 60% on the Tibetan Plateau.