[M-IS15] 古気候・古海洋変動

[MIS15-P08] Analysis of factors contributing to the differences between Pliocene and present-day climates using an atmosphere-ocean-vegetation coupled model: CO₂ vs. geographical conditions

*中川 祥緒¹、阿部 彩子¹、陳 永利¹、樋口 太郎¹、大石 龍太¹、小長谷 貴志¹ (1.東京大学)

キーワード：気候モデル、古気候、鮮新世

It is known that glacial-interglacial cycles began around 2.7Ma. The initiation of the glacial-interglacial cycles has been thought to be due to a decrease in atmospheric CO₂ concentration, which caused a global cooling. On the other hand, some studies suggest that, in addition to the change in CO₂ concentration, differences in geographical conditions, such as land-sea mask and ice sheets, could also have caused the differences between the climate before the glacial-interglacial cycles and that of present-day. In this study, we analyzed the results of experiments conducted with MIROC-LPJ in which CO₂ concentration and geographical conditions were changed to those of present-day and Pliocene separately. The difference between temperatures in the experiments with different geographical conditions was larger than that in the experiments with different CO₂ concentration. Around the regions where the geographical conditions changed greatly, the difference in temperature due to this change was larger than the difference due to changes in CO₂ concentration. The climate also changed in other areas, through changes in vegetation and atmospheric circulation associated with the change in temperature. Around the Hudson Bay, which was land in the Pliocene, it was more likely to be warm in summer and cool in winter compared to present-day. From this result, it is thought that, although it was difficult for the Northern Hemisphere ice sheets to grow under Pliocene geographical conditions, after initiation of the glacial-interglacial cycles due to a decline in CO₂ concentration, ice sheets grew more easily as the Hudson Bay formed.