Global warming is one of the biggest environmental concerns, in which the rising content of atmospheric CO2 was once widely considered as the main contributor. However, in recent years, growing studies show that, solely by the greenhouse effect of CO2 itself, it appears far less to drive the temperature soaring up to the monitored magnitude. Similarly, mismatches between atmospheric CO2 and temperature in the geologic past are also increasingly detected. These facts strongly imply that, except for CO2, there must have been other and more powerful driving force. In the present study, we focus on the water vapor, another important greenhouse gas, which greenhouse effect doubles to that of CO2. Based on results of previous NSFC Project to the principal investigator, floras from the Taipinglinchang, Wuyun, and Dalianhe formations of Jiayin and adjacent Luobei counties are carefully selected in the present study to investigate the greenhouse effect of the water vapor. These 3 floras represent 3 important greenhouse stages of the Campanian, Selandian, and Lutetian, respectively. Temperature of each stage will be reconstructed by the leaf physiognomy analysis, while the corresponding paleo-CO2 will be estimated by Gingko leaf cuticles. Relational model between water vapor and temperature will be established in basis of data analysis on high-resolution modern climatic data. Then the model will be used in paleoclimate study to find out the contribution of water vapor to temperature changes. The final aim of this study is to determine if water vapor is the primary factor to climatic change, which will provide a new way to understand paleoclimate.