The authors say that temperatures at the poles were five to nine degrees higher 125,000 years ago. Yet CO2 levels were considerably lower – at 280 ppm.
Whatever was driving the higher temperatures was not CO2. Co-author Michael Oppenheimer apparently failed to recognize the key logical finding of his study.
Besides that problem, another issue is that it would require many thousands of years to melt enough ice to raise sea levels that much. All of the ice in Greenland would have to melt. There are only a few weeks a year where melt is even remotely possible in the interior of the ice sheet. Last summer never got above freezing in Greenland’s interior.
Sea level has been rising at a steady rate of six inches per century. It will require 4,000 years for sea level to rise 20 feet.