One item not yet discussed here is another factor at play leading to a vicious circle acceleration of a natural global change; namely the shifting of the magnetic poles which has happened a few times already and it's migrations have been mapped by several means including studying the reversal of magnetic positionings of core samples in ancient lava. ( Magnetically reaction metals being fliud enough to react when in molten form ; Iceland being on of the more active natural laboratories )
So , rather than a permnent total global warming it's more a case of the globe having already begun its axial shift and , as a result , polar ice is melting in one place and is supposed to re-crystalize elsewhere.
What global warming is doing is preventing the balance of re-freezing and exacerbates whatever nature's reaction to this imbalance. All depends upon what is the core cause of this periodic axis shift. Some theorize it is caused by the weight of the polar ice caps progressivel throwing the Earth's rotation off until it reaches that event horizon line. Others posit that the periodic planetary allignments of critical mass gravitation ( Yeah ,the old "Jupiter Effect" which already happened sometime in the 80's I think ) which triggers enough of a establizing wobble that steadily grows until balance corrected.
Oh ,and the best evidence about the nature of time frame in which a polar shift occurs comes from the discovery on ancient
Mastadons ( Wooly Mammoths ) found frozen in the Russian /Central Asian Tundra with undigested prehistoric flowers still in their stomachs . For a group of animals , already adapted for cold weather , to be frozen before digesting some still fresh Sprng flowers suggests how fast it happens; ie well within a 12 hour period.
So make sure you have plenty of film or DVtape in the camera, folks, this could be quite a ride. ;-)