I'll be watching this string, because it's a very good question. With the pair historic/historical there's a clear difference.
On this historic occasion, we salute the men who ....
It is a historical fact that ....
The first means 'making or marking a significant event'; the second means 'pertaining to an event known to have taken place'.
But some of your examples aren't that clear. In general, I'd guess that '-al' tends to distance the speaker from the word:
It's a theoretical possibility
It's a theoretic certainty.
His equipment was scientifical, but his methods were not scientific
Geographic North is not the same as magnetic North
The explorer's intentions were purely geographical
I'm running out of ideas here. Let's hope there's a simple rule!
PS - When you make either of these pairs into an adverb, it's '-ically'