"About 20,000 years ago, the climate warmed and the ice sheet retreated. Water from the
melting glacier filled the basinsoffsite link, forming the Great Lakes. Approximately 3,000 years ago, the Great Lakes reached their present shapes and sizes."
This lake system contains the largest supply of freshwater in the world.
www.noaa.gov
So, 17,000 years for the ice to melt.
You deniers really have difficulty hanging on to the important bits. And just about the most important bit with global warming is the RATE at which it is happening. If the planet spent ten thousand years warming up 5C, no one would notice or give a shit. But when it happens fifty times that quickly, there will be real problems that have to be dealt with. People are going to suffer and there will be enormous expenses trying to deal with it. And, like
any problem, closing your eyes, sticking your fingers in your ears and chanting "na-na-na-na-na-na" is the choice of imbeciles.