In Anno1404, you could build docks (or maybe something else, I am not sure I remember correctly), each of which would increase the capacity of the warehouse. I couldn't find anything equivalent in Anno2070. Is it possible to increase warehouse capacity (apart from upgrading it) ?
The building that you're looking for that equates to the docks in 1404 is the Harbor Depot. In addition to being able to upgrade your Port Authority Warehouse by clicking in the top right corner, you can build these buildings. They'll store 40 more tons of goods.