Reconstructing atmospheric CO 2 during the Plio–Pleistocene transition by fossil Typha

The Earth has undergone a significant climate switch from greenhouse to icehouse during the Plio–Pleistocene transition ( PPT ) around 2.7–2.4 million years ago (Ma), marked by the intensification of the Northern Hemisphere glaciation ( NHG ) ~2.7 Ma. Evidence based on oceanic CO 2 [( CO 2 ) aq ], supposed to be in close equilibrium with the atmospheric CO 2 [( CO 2 ) atm ], suggests that the CO 2 decline might drive such climate cooling. However, the rarity of direct evidence from [ CO 2 ] atm during the interval prevents determination of the atmospheric CO 2 level and further assessment on the impact of its fluctuation. Here, we reconstruct the [ CO 2 ] atm level during 2.77–2.52 Ma based on a new developed proxy of stomatal index on Typha orientalis leaves from Shanxi, North China, and depict the first [ CO 2 ] atm curve over the past 5 Ma by using stomata‐based [ CO 2 ] atm data. Comparisons of the terrestrial‐based [ CO 2 ] atm and the existed marine‐based [ CO 2 ] aq curves show a similar general trend but with different intensity of fluctuations. Our data reveal that the high peak of [ CO 2 ] atm occurred at 2.77–2.52 Ma with a lower [ CO 2 ] aq background. The subsequent sharp fall in [ CO 2 ] atm level might be responsible for the intensification of the NHG based on their general temporal synchronism. These findings shed a significant light for our understanding toward the [ CO 2 ] atm changes and its ecological impact since 5 Ma.