You can do it empirically -- just check the total in the advisor (F5) before you go to your next turn, and write down the number (or enter it into CALC.exe). Next turn when you get a chance, go back to the advisor and see how much it has changed.
You can predict it already, but it would require you manually add up every city... which makes for sucky micromanagement!. Having the per-turn totaled up already would be very nice. Also, if it showed somehow the "war penalty" that would be very good also.
Have an easy way to compare per-turn with the other cultures would be too much to ask I'm sure... you can do an estimate using the score screen...
Cheers,
Shawn