Since the 19th century, the study of archaeobotanical remains has been very important for combining “strict” archaeological knowledge with environmental data. Pollen data enable assessing the introduction of certain domesticated species of plants, or the presence of other species that grow typically where humans dwell. Not all pollen data come from archaeological fieldwork, but the relationship among the two sets is strong enough to take an interested look at pollen data worldwide, their availability and most importantly their openness, for which we follow the Open Knowledge Definition.
The starting point for finding pollen data is the NOAA website.
The Global Pollen Database hosted by the NOAA is a good starting point, but apparently its coverage is quite limited outside the US.