Debates on mitigation and adaptation measures to adopt against climate change are based on observations and estimations over a range of less than 250 years. A recent study by Clark and his collaborators, published in Nature Climate Change, covers extremely long term (over 10,000 years1) climate consequences. Their scope is linked to CO2 emissions. According to these scenarios, the temperature increase could exceed the 2°C limit, and a 2 to 4 meters per century sea-level rise could be expected in the next millennium. These results confirm the importance of keeping a large quantity of fossil resources untouched.
Over the geological era, the chemical state of the ocean determines its ability to absorb atmospheric carbon dioxide gas, and therefore to contribute to the Earth climate regulation. Its state depends on the balance between sources and departures of any element delivered to the ocean, both terms extremely difficult and complex to quantify. This article reviews the state of knowledge on dissolved and particulate contributions to the ocean issued from the land-ocean interface (continental flux) on one hand and from the oceanic crust – ocean interface (hydrothermal flux) on the other hand.
Each day, the oceans absorb about a quarter of the CO2 produced by human activities, causing a chemical modification of seawater that results in ocean acidification. The disso- lution of CO2 in seawater causes an increase in acidity (decrease in pH) and a decrease in the availability of carbonate ions (CO32-) which are one of the building blocks required by marine plants and animals to make their skeletons, shells and other calcareous structures. Ocean acidity has increased by 30% in 250 years, and could triple by 2100. It threatens species such as oysters and mussels, and will also have an impact on marine food chains. Our understanding of the effects of ocean acidification on marine life is still only rudimentary.