What is ocean acidification?

The ocean, as immense and majestic as it may be, is much more than just a postcard setting. It plays a fundamental role in the climatic balance of our planet: each year, it absorbs around 25% of carbon dioxide emissions from human activities. A phenomenon that, at first glance, seems beneficial in limiting global warming.

But this capture capacity has a worrying downside: it leads to a chemical modification of marine waters, a process called ocean acidification.

When CO2 dissolves in water, it reacts with the molecules present and causes a drop in ocean pH. Since pre-industrial times, the pH of the oceans has dropped from 8.2 to 8.1. This may not seem like a big deal, but this decrease represents a 30% increase in ocean acidity in just two centuries, an upheaval of unprecedented magnitude on a geological scale.

Ocean acidification poses a dual threat. First, it weakens marine ecosystems by disrupting organisms that depend on limestone to grow, such as corals, shellfish and certain phytoplankton. Corals, which are true havens for biodiversity, are gradually bleaching and dying, jeopardizing an entire food chain. Fish and crustaceans, which depend on them, are also seeing their development threatened.

Then, this chemical alteration has direct repercussions on human populations. More than three billion people in the world depend on marine biodiversity for food or for their economic activity, particularly fishing and aquaculture.

In France, the Mediterranean is particularly affected: between 2007 and 2015, its acidity increased by 7%, one of the highest rates observed to date. At the same time, its temperature rose by 0.7°C, a warming much faster than the global average.

Faced with this threat, the effective solution is to reduce CO2 emissions on a global scale, according to experts. This implies ambitious climate policies, but also local actions to protect our coastal ecosystems, limit agricultural discharges and promote more sustainable management of marine resources.

With the second largest maritime area in the world, France has a particular responsibility in this fight.