As long as you set the variable in the variable editor, it's global.. to prove that, make a new trigger and only set a variable in it.
-
Set bla = (Triggering unit)
It will look like this
Then convert the trigger into jass and it will look like this
JASS:
Set udg_bla = GetTriggeringUnit()
or similar.
udg stands for user defined global (as far as i know and is therefore global