Lose weight all over your body or get it surgically removed. There isn't a way to target fat loss in a certain area. Step up your cardio.
Losing back fat is like losing fat anywhere else on your body... When you do your cardio, when you're done work on your obliques, that should put some muscle on you and stretch your back skin tighter so it won't look so... I don't know whatever you want to call it. Also work on abs, anything you can do to gain muscle and stretch the skin you have will look much better than doing any kind of surgical operations. and before you think about surgery please, please give the cardio and ab and obliques a try for a min of 4-6 months. And remember... it's not how much you do but the quality and form of what you do, do that counts.fat rib cage