If all the ice melted

If we keep burning fossil fuels indefinitely, global warming will eventually melt all the ice at the poles and on mountaintops, raising sea level by 216 feet.
By releasing carbon dioxide and other heat-trapping gases into the atmosphere, we have warmed the Earth by more than a full degree Fahrenheit over the past century and raised sea level by about eight inches. Even if we stopped burning all fossil fuels tomorrow, the existing greenhouse gases would continue to warm the Earth for centuries. We have irreversibly committed future generations to a hotter world and rising seas. 

 The concentration of carbon dioxide in the atmosphere has surpassed 400 parts per million, the highest since three million years ago. Sea levels then may have been as much as 65 feet above today’s; the Northern Hemisphere was largely ice free year-round. It would take centuries for the oceans to reach such catastrophic heights again, and much depends on whether we manage to limit future greenhouse gas emissions. In the short term scientists are still uncertain about how fast and how high seas will rise. Estimates have repeatedly been too conservative.

Global warming affects sea level in two ways. About a third of its current rise comes from thermal expansion—from the fact that water grows in volume as it warms. The rest comes from the melting of ice on land. So far it’s been mostly mountain glaciers, but the big concern for the future is the giant ice sheets in Greenland and Antarctica. 12 years ago the Intergovernmental Panel on Climate Change (IPCC) issued a report predicting a maximum of 23 inches of sea-level rise by the end of this century. But that report intentionally omitted the possibility that the ice sheets might flow even more rapidly into the sea, on the grounds that the physics of that process was poorly understood.

Climate scientists now estimate that Greenland and Antarctica combined have lost on average about 50 cubic miles of ice each year since 1992—roughly 200 billion metric tons of ice annually. Many think sea level will be at least three feet higher than today by 2100. Even that figure might be too low. Coastal cities face a twofold threat: Inexorably rising oceans will gradually inundate low-lying areas, and higher seas will extend the ruinous reach of storm surges. The threat will never go away; it will only worsen.
Using a conservative prediction of a half meter (20 inches) of sea-level rise, the Organization for Economic Co-operation and Development estimates that by 2070, 150 million people in the world’s large port cities will be at risk from coastal flooding, along with $35 trillion worth of property—an amount that will equal 9 percent of the global GDP. How will they cope?