Ocean acidification has become over the last few years one of the main problems that our oceans face. Unfortunately, this issue is not visible to the naked eye, and the impacts aren’t as noticeable as increasing temperatures or sea level rise. Consequently, very few people know about it or care about it.
- What is ocean acidification?
CO2 is naturally present in the air we breathe: plants need it to grow, and animals exhale it. But since the industrial revolution, the level of CO2 in our atmosphere has been increasing. Most of it ends up in the atmosphere, and hence warms up our planet. About 30% of that CO2 dissolves in the oceans, leading to chemical reactions that reduce the pH of seawater.
Over the last 10 years, scientists have realized that the excess CO2 resulting from all the anthropogenic activities has actually changed the chemical composition of our oceans. The more pH decreases, the more our oceans become acid. According to the Smithsonian, pH has gone from 8.2 to 8.1 since the industrial revolution, and they expect that it will continue to decrease by 0.3 before the end of the century.
A decrease of 0.1 doesn’t seem like a big deal, but the pH scale is logarithmic. For example, pH 4 is 10 times more acid than pH 5. Consequently, if the CO2 emissions continue at the same rate, it is possible that the pH decreases down to 7.7, making our oceans more acid than ever. This change in only 0.1 already represents a 30% increase in the acidity of our oceans (Rhein et al. 2013).
“Ocean acidification” thus refers to the decrease in pH caused by the increasing CO2 absorption by our oceans.
- What are the consequences on marine life?
A certain number of marine animals (corals, mussels, oysters etc…) use part of the carbon naturally present in our oceans to form their skeleton or shells. By trapping the carbon that way, they limit the formation of carbonic acid and thus slowly contribute against the process of acidification.
However, a more acid environment weakens these organisms that are very sensitive to changes in pH. The more acidity increases, the more energy they need to create their shells or skeletons. They become more vulnerable, using more energy to form their shells, and hence face problems with predators, feeding and reproduction.
This change in pH occurred so quickly that many animals didn’t have time to adapt, and their shells or skeletons are now slowly dissolving. A study published in 2012 in Nature Geoscience showed the corrosive effects of ocean acidification on the shells of pteropods, a small organism that is essential to the food chain.
- Why should I be concerned?
Everything in our oceans is connected, and ocean acidification has an important impact on the food chain. Zooplankton is the base of the food chain, and is constituted of small micro-organisms that also need a shell to survive. With ocean acidification, these organisms have a hard time surviving and reproducing, and the entire food chain is at risk.
Hundreds of species of fish, corals or sharks depend on zooplankton to live. Moreover, many nations need the oceans to thrive, as their economies are heavily based on tourism and fisheries. Food safety of these populations and global marine biodiversity are threatened by ocean acidification.
- What can I do?
The first step is to reduce our emissions of CO2 in the atmosphere. This can be done at the national and international level between politicians and policy makers (that is the goal of the COP21), but also at the individual and local level, where everyone can aim to use more sustainable energies.
The exact consequences of these changes in pH are still uncertain, and a more acidic ocean is not going to destroy all the marine life. But the scientific consensus is that the 30% increase in acidity is already affecting many organisms. If acidification continues, it is possible that some species become rarer, or even extinct.
In the next article related to ocean acidification, I will go over 5 simple steps everybody can do in their daily lives to use less energy and to help reduce CO2 emissions. Everyone can do their part in fighting ocean acidification!
This article was originally published in French on the Ocean For Climate’s blog for the newspaper Le Monde: Tout ce qu’il faut savoir sur l’acidification des océans.