Put an ice cube in a glass filled to the brim with water and the water will not spill when the ice melts: this is the ice cube effect. Similarly, when ice floes melt they do not cause sea levels to rise.
And yet sea levels are rising. This is still at a modest rate: an average 0.07 in. (1.7 mm) per year during the 20th century, and by 0.12 in. (3.1 mm) more recently. There are two reasons why. The first is that oceans expand as they become warmer. The second is that the world’s glaciers—the Andes and Himalayas, for example—are melting, and their water is flowing into the oceans via rivers. If these glaciers disappear completely, they will cause a rise in sea levels of around 19.5 in. (500 mm). But even that is nothing compared to what would happen if the ice of Antarctica and Greenland were to disappear: a rise of 183 feet (56 meters) and 19 feet (6 meters), respectively.
Given that the temperature at the South Pole drops to -94°F (-70°C) in winter, there is no question that the whole Antarctic ice cover could disappear in the foreseeable future. But Antarctica is an immense continent, with greatly differing regions. In some regions, for local reasons, the snow cover is actually increasing slightly. In others, in the west (near Argentina and Chile), the glaciers are undoubtedly melting. But, for the moment, the continent is showing no clear signs of extensive change due to global warming.
The situation in Greenland is far more worrying. Until recently, experts thought that global warming would have only a modest impact here. This seems not to be the case. The melting of surface ice is causing flow at deeper levels, which in turn is having a lubricant effect, encouraging the movement of ice towards the sea and accelerating the melting process. These past few years, Greenland has thus been melting much faster than predicted.
The fate of Greenland and Antarctica, and of our oceans and coastlines, depends on greenhouse gas emissions occurring sometimes thousands of miles away, whether in Los Angeles, Beijing, or Paris. Global warming is a planetary phenomenon. Its global impact creates a new form of collective responsibility, since every single one of us is responsible for a part of these gas emissions. It calls for the emergence of a new form of solidarity.