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) 2.7Ma. Evidence based on oceanic CO2 [(CO2)(aq)], supposed to be in close equilibrium with the atmospheric CO2 [(CO2)(atm)], suggests that the CO2 decline might drive such climate cooling. However, the rarity of direct evidence from [CO2](atm) during the interval prevents determination of the atmospheric CO2 level and further assessment on the impact of its fluctuation. Here, we reconstruct the [CO2](atm) level during 2.77-2.52Ma based on a new developed proxy of stomatal index on Typha orientalis leaves from Shanxi, North China, and depict the first [CO2](atm) curve over the past 5Ma by using stomata-based [CO2](atm) data. Comparisons of the terrestrial-based [CO2](atm) and the existed marine-based [CO2](aq) curves show a similar general trend but with different intensity of fluctuations. Our data reveal that the high peak of [CO2](atm) occurred at 2.77-2.52Ma with a lower [CO2](aq) background. The subsequent sharp fall in [CO2](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 [CO2](atm) changes and its ecological impact since 5Ma.