So says a group of Antarctic researchers if drastic cuts in greenhouse emissions are not achieved. Their study published in the respected journal, Nature, concludes that a global temperature increase of only 5.4℉ (3℃) above the pre-industrial norm will cause ice shelves to melt. These huge floating slabs of ice hold back the even more enormous continental ice sheets which would be loss over the next few centuries. The great melting means that sea levels will rise catastrophically for thousands of year, contributing as much as 9 meters to long term sea rise.
The study by Golledge et al is not all gloom, if humanity acts to save itself. If temperatures remain with 3.6℉ (2℃) the collapse will stabilize and the ice sheets remain mostly intact. To achieve this, the planet as a whole must follow the IPCCs lowest emissions scenario. Under this scenario global emissions will peak around 2020 and decline to zero or below by 2100. Nations attending the Paris climate conference next month have submitted pledges to cut and reduce emissions. But those are not enough according to one analysis. They cause a 2.7℃ warming, not enough to avoid collapse.
In 2014 Eric Rignot working for NASA discovered that the massive west Antarctic ice sheet is already slipping into the ocean. Global sea levels have risen roughly 8 inches over the past century, most of it from natural expansion of warming oceans. But if the ice sheets give way the rise in sea levels will be dramatic because the size of Antarctica's two ice sheets cover an area the size of the United States and Mexico. They are held in place on the continent by buttressing ice shelves. Satellite surveys show the floating shelves are losing 310km² of ice every year. If lost completely, seas would rise 60 meters according to the US National Snow and Ice Data Center. Goodbye New York, New Orleans and Miami.