Eventually the fresh water influx into the oceans causes the deep ocean currents - which keep the oceans at pretty much the same temp and move heat around to maintain stable climates - are disrupted and the earth could end up in a new ice age.
Why will the fresh water influx disrupt the deep ocean currents and why will disrupting the currents cause an Ice Age?
It seems to me that if the North Pole melts, part of the Japanese current will flow through the North Pole an into the Atlantic rather than all of it going down the west coast of North America. This would increase the flow of the deep ocean currents rather than decrease them.
When seawater freezes at the poles, it leaves behind very salty, very cold (and hence very dense) water, which sinkes and flows along the ocean floor. Surface currents are partially driven by water flowing in to replace this sinking water (and partially by the prevailing wind patterns).
There was a theory that polar warming could disrupt the Gulf Stream/North Atlantic Drift (which transports heat from low the Caribbean to Europe, and stops England being as cold as Newfoundland), thereby cooling Europe. However, I'm not sure if this theory is still considered likely. Besides, if current warming is part of the natural glacial/interglacial cycle, we shouldn't be due another ice age for quite some time.
Decreasing albedo as a result of melting ice caps is more likely just to result in the earth getting even warmer.
