We hear regularly some warnings of scientists on the important rise of the sea level that will occur before the end of the century. The worst scenario usually predicts a rise of less than a meter before 2100.

Where does this number come from? The common answer is that the rise of the sea level comes both from the melting of glaciers and the dilatation of the seawater due to the increase of its temperature.

I have made the exercise of calculating the volume of the glaciers of Greenland and Antarctica. The area of glaciers in Greenland is 1,775,637 km^2 and their volume is 2,850,000km^3. The area of Antarctica is 14,000,000 km^2 and the thickness of ice is up to 3km. If we take a mean thickness of 2km, then this gives a volume of 28,000,000 km^3.

Hence, the total volume of ice of the glaciers of Greenland and Antarctica is of the order of 30,850,000 km^3. Now, the area of the oceans is 335,258,000km^2. Hence, if all glaciers were to melt and produce the same volume of water (OK, it is a little less, but the water will dilate when its temperature increases) we would have a rise of the sea level of 92 meters!

Can we explain the difference? Of course, my model is very rough. It is not clear that all the new water will stay in the oceans. Some could percolate in the soil, and some could evaporate in the atmosphere. I have asked the question recently to Hervé Le Treut, from the Institut Pierre Simon Laplace in Paris. His answer was that the ice melts slowly, and hence it takes much more than 90 years for all the glaciers to melt.

But it raises another question. Why do we stop our predictions in 2100? Is sustainability no more necessary past 2100?

Christiane Rousseau