I suppose 'Global Warming' has two meanings =) The literal and the name tag applied to the theory. If I recall correctly - doesn't the periodic 'warming' cause the cooling? Due to the ice deposits melting, and reducing the salinity of the oceans, which interferes with currents and also makes the less salty oceans freeze more easily? In very simple terms!
I bet convincing humanity that THEY were the CAUSE of an Ice Age (via 'causing' global warming), would generate a huge amount of guilt on top of the fear and more practical difficulties!
What you are talking about is a disturbance/collapse of water currents. That can have a major impact on heat/humidity distribution. Now could that alone provoke a glacial rebound? Maybe, but I'm not sure.
But here what is important to consider is that if indeed our axis is slowly shifting, that alone could provoke a major drop in T° at least in some area(s) which then could suffer from drastic precipitation as a result of increasing air water content due to the current 'warming'.
If that was to happen, the accumulation of ice/snow on a large area could instantly decrease the radiation forcing of the earth and possibly lead us (very quickly) to a new ice age, just like a snowball (appropriate word) effect.
Si in résumé
, current 'warming' could be viewed as a potential catalyst for potential glacial rebound.