The article to read to understand the importance of the oceans in the fight against climate change


The goal is to protect the oceans. The One Ocean Summit opens in Brest on Wednesday February 9. “Scientists, economic and regional actors” come together to prevent the “destruction of biodiversity”, in the words of Emmanuel Macron. Because by his activities, man upsets the continents, but also the oceans. “They are clearly a major issue in the fight against climate change. It is very important to better understand the different changes that are expected there”, explains Caroline Muller, researcher at the Dynamic Meteorology Laboratory. To do this, franceinfo details the close links between global warming and the oceans.

Why are the oceans and the climate linked?

First, the ocean and the atmosphere exchange heat. “Solar radiation heats it. Hot currents then transport this energy to other places and return the heat to the atmosphere”describes Eric Guilyardi, researcher at the Laboratory of Oceanography and Climate.

“The oceans are thus a giant thermostat.”

Eric Guilyardi, climatologist and oceanographer

at franceinfo

Then, like forests, the oceans represent a carbon sink: when the latter is found in excess in the atmosphere, the oceans will absorb part of it and store it, in algae or phytoplankton, for example. “Human activity emits about 10 billion tons of carbon per year: 45% remains in the atmosphere and 25% to 30% is absorbed by the ocean”explains Eric Guilyardi.

What is the impact of human activity on the oceans?

Global warming caused by human activity is not without effect on the oceans. Thus the temperature of the oceans was higher by 0.88°C between 2011 and 2020 than between 1850 and 1900, according to the latest report (in English) of the Intergovernmental Panel on Climate Change (IPCC). “The ocean has warmed faster over the past century than since the end of the last deglaciation 11,000 years ago”, they write. A warming clearly visible by observing the anomalies in the annual average temperature of the oceans compared to the normal temperature:

What are the other consequences?

When the temperature of the water increases, it expands. Mélanie Becker, researcher at the Littoral, environment and societies laboratory, illustrates:

“If you take a bottle of water out of the fridge in the summer and put it on a table in the sun, you will hear crackling sounds, because the container heats up and the volume expands.”

Mélanie Becker, researcher

at franceinfo

To this expansion of the water must be added the melting of the polar ice caps and glaciers caused by the warming of the atmosphere. Result: if during the 20th century the sea level rose by 1.5 mm per year on average on Earth, “Since the 1990s, this rate has doubled to 3.5 mm per year”, warns Mélanie Becker, stating that this increase may vary between regions. According to the latest IPCC report, the rise in water levels could reach up to 1 meter by 2100 without ambitious action to reduce our greenhouse gas emissions.

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This elevation poses a major challenge for coastal populations. “Today, 20% of the world’s population lives less than 30 km from the coast and 10% live in very low altitude lands”, explains Mélanie Becker, who cites the example of the Ganges delta, in Bangladesh, where the water could rise by 1.40 m. Similarly, in Indonesia, the entire northern coast of the island of Java is disappearing and the authorities plan to relocate the capital Jakarta and its 11 million inhabitants. In the Pacific, some of the Solomon Islands have already been submerged.

It’s pretty good that the oceans absorb CO2, isn’t it?

“A priori this is good news, but the dark side is that this absorbed CO2 has consequences on the chemistry of the ocean”, nuance Laurent Bopp, researcher at the Dynamic Meteorology Laboratory. Indeed, when the ocean absorbs CO2, it becomes acidic. And this change in PH affects marine ecosystems and in particular the ability of certain organisms to build their shells and skeletons. The researcher cites coral, zooplankton and even pteropods.

Dead corals caught on camera in Kimbe Bay, Papua New Guinea, in November 2017. (CHRISTOPH GERIGK / BIOSPHOTO / AFP)

“In scenarios where greenhouse gas emissions continue to increase, it can be shown that this acidification of the ocean could lead to corrosive chemistry for these calcifying organisms like corals and would lead to their dissolution”, continues Laurent Bopp. His colleague Eric Guilyardi illustrates the phenomenon with an experiment “exaggerated” : “If you dip a shellfish in vinegar, which is very acidic, you can see the degassing and its dissolution with the naked eye.”

What are the risks for biodiversity?

Climate change affects species in two other ways. The warming temperature at the surface will cause “a stratification of the ocean”. That is to say that the surface and deep layers will communicate less with each other and “nutrient flows up from the depths [où chute la matière organique consommée en surface] towards the surface will be less”, draws Laurent Bopp. And the researcher adds:

“When the ocean is warmer, gases are less soluble in it and it absorbs less oxygen.”

Laurent Bopp, climatologist and oceanographer

at franceinfo

These under-oxygenated areas could thus reduce the habitat areas of certain species, “like tropical tunas, which need a lot of oxygen”, quotes Laurent Bopp. Cascade, “These risks weigh on the entire food chain”he concludes.

The species are, moreover, under fire from other threats such as overfishing or plastic pollution or other pollution of human origin. In total in the oceans, the red list (in English) from the International Union for Conservation of Nature (IUCN) reports 5 extinct species, 194 critically endangered, 323 endangered and 767 vulnerable.

How can we protect the oceans?

Marine protected areas are today the main tool for protecting the ocean. “Globally, they cover around 8% of coastal and marine waters. It varies between countries: France claims 30% of its waters protected by the system”, describes Joachim Claudet, researcher at the Center for Island Research and Environmental Observatory (Criobe). He cites the example of the marine nature reserve of Cerbère-Banyuls, in the Pyrénées-Orientales, where “studies show that the protection is effective”.

A red lionfish is photographed in the marine nature reserve of Cerbère-Banyuls (Pyrénées-Orientiales), January 30, 2014. (MURIEL DUHAU / BIOSPHOTO / AFP)

These marine areas, however, exclude areas on the high seas, which are beyond national jurisdiction. The subject is at the heart of negotiations at the moment at the UN. (in English)with the treaty on marine biodiversity of areas beyond national jurisdiction. “It aims to coordinate efforts for the conservation and sustainable use of biodiversity in the high seas”explains Joachim Claudet, who specifies that the negotiations are nearing completion.

Are these measures sufficient?

Marine protected areas are not always effective. “There are a very large number of forms, with a whole range of possible rules”, regrets Joachim Claudet. From fully protected areas where uses that pose a threat are simply prohibited to others where no binding regulations are in place, protection is not equal everywhere.

“60% of the French Mediterranean is in a marine protected area. We can ask ourselves questions about the effectiveness of the protection. If it really were, the Mediterranean would undoubtedly have another aspect…”

Joachim Claudet, researcher

at franceinfo

The impacts of human activities are still visible “in an overwhelming majority of marine protected areas”, he expands. The researcher therefore expects from the One Ocean Summit of the “clarity” on protective measures: “Until now, we have sought quantity, arriving at an astronomical number of marine protected areas. Now we are asking for quality, with truly protected ecosystems. Because to increase their resilience in the face of climate change, the human pressures are limited.”

Moreover, all the researchers interviewed defend greater consideration of the ocean in the fight against climate change. “It’s not enough today. Our food security, the disappearance of ecosystems, the redistribution of species are at stake. There are a number of phenomena linked to the dynamics of the oceans and the spectrum of impacts is very broad”, underlines Mélanie Becker. If he is happy that the subject is better considered “since COP21”Eric Guilyardi agrees: “For scientists, the ocean has always been at the heart of the climate.”

I didn’t have time to read everything, can you give me a summary?

Climate change does not only affect the continents. The ocean is also affected in different ways. If it absorbs part of the CO2 that we emit, the ocean also suffers the consequences: by chemical reaction, it becomes acidic, threatening ecosystems that are not very viable in an environment that is too corrosive. Just like the atmosphere, the temperature of the water is warming too. And when water heats up, it expands. It is one of the main causes of sea level rise, which threatens 20% of the world’s population. Faced with these risks, protection tools have been put in place. Marine protected areas try to protect these environments from human pressures, but they are often not very effective, according to the researchers. They therefore expect the international community, particularly during the One Ocean Summit, to take concrete action to preserve this essential cog in the climate system.



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