In recent years attention has been given to assess the impacts of warming on the plant flowering phenology. There is a growing realization that herbarium-based collections could offer a reliable and relatively time-saving baseline data source to identify these effects. This article examines the magnitude and trends of warming effects on the average flowering timing (AFT) of plants in Tibet Autonomous Region using analysis of herbarium specimens collected for 4 decades. Mixed model with randomized blocks was used to analyze a set of 41 species (total 909 specimens) which were collected during the period of 1961–2000. Results showed that an earlier AFT emerged within 40 years period in comparison to the recorded data of the year of 2000 (0.5 days per year), and that 7.5 days early flowering was contributed by mean summer (i.e., June–August) temperature. It is proposed that temporary shifts in flowering phenology responding to continuing temperature rise could quantify the extent to which climate affects plant species. Analysis of well recorded herbarium specimens could provide a reasonable indication on the impacts of rising temperature on plant phenology. The result of this study could also facilitate a bridge between the scientific knowledge and indigenous knowledge of Tibetan communities.