The mere fact that 68,000 year old ice exists is demonstrates that the climate has failed to warm sufficiently to melt it all, even in periods known to have been warmer than current times.
As you can see in the following grapic, 68,000 years ago, the earth was deep in the last ice age. Also note that that ice age extended backward in time another 80,000 years.
jibbles
Feb 5, 2013