You can have global variables by creating Global Blackboards through the “Tools/ParadoxNotion/NodeCanvas/Create/Global Scene Blackboard” menu command. Global Blackboards are added in the scene and as such you can have scene object references assigned in their variables. Global Blackboards are persistent between loading scenes (DontDestroyOnLoad) and you can have as many as you wish.
For each GlobalBlackboard in your scene though, you must specify a completely unique name in its inspector.
Later on, whenever you encounter a BBParameter for variable selection, you will see the global variables categorized underneath the GlobalBlackboard’s name as illustrated bellow.