The Weather-Climate Question: Why are water levels rising?

A country forced to move its capital. To replace Jakarta, which was regularly flooded and sinking, Indonesia had to inaugurate a new city, announced as carbon neutral and protected from rising waters. When discussing this problem, we also often think of the Pacific islands.

However, this phenomenon is not limited to distant lands. In France too, certain regions such as Gironde, Vendée and Camargue are on the front line facing rising waters.

Why are sea levels rising and what are the consequences? The phenomenon is mainly due to two causes.

First, the melting of ice. The ice caps of Greenland and Antarctica, as well as mountain glaciers, such as those in the Alps, are melting at an accelerated rate due to global warming. This melting releases large quantities of fresh water that swell the oceans.

But also thermal expansion. This process, less known, is nonetheless just as important. When water heats up, its molecules expand and its volume increases. Imagine a pot of water on the stove: the hotter it gets, the more it threatens to boil over. The ocean works in the same way.

Scientists are sounding the alarm because sea levels are rising dangerously fast. While in the last century, sea levels were rising by 1.7 mm per year, this rise has now been 3.3 mm each year since the 1990s. This may seem insignificant – barely the thickness of two 1 cent coins – but over several decades, the consequences are major.

Rising water levels are causing the destruction of coastal ecosystems, the submersion of certain land areas, the salinization of soils and the intensification of extreme weather events, such as cyclones.