Use of Instants During Combat Phase
The Grizzly Bears don't deal combat damage to the Air Elemental

Assuming no more instants or abilities are added to the stack after Shock, the stack will resolve. 

First, Shock will resolve, causing your bears to die. 

Then, Titanic Growth will resolve: it can't find the creature you targeted, so it effectively does nothing.

Finally, since the stack is empty and players have passed priority, we move to combat damage. There are no attackers, so no combat damage is dealt.