Global greening refers to expansion of the terrestrial biosphere as a result of changes in atmospheric chemistry. There are three main ways that global greening can happen. 1: Increased temperatures and/or rainfall will allow plants to grow where they previously could not. 2: Increased atmospheric carbon dioxide enhances photosynthetic activity and thus should result in increased biomass. 3: Increased atmospheric carbon leads to less transpiration due to reduced stomatal conductance, making them effectively more drought resistant. Add those three mechanisms together and we should expect the future to be much greener than today. Unfortunately, that does not seem to be the case. Anthropogenic changes appear to be too fast for many of these key mechanisms to function as they would in an idealized scenario. However, during the warmer world and elevated CO2 levels of the Miocene, the biosphere may indeed have expanded due to these global greening mechanisms. In this talk, we'll explore how Miocene fossil plants reveal a globally greener world, and what may have contributed to this expanded terrestrial biomass.