Françoise Gaill: “The heat absorbed by the ocean ensures that we can still live”

Can we imagine in concrete terms what this figure means? Between the expansion of an ocean that gains volume as it warms, on the one hand, and the melting of terrestrial glaciers on the other, the rise in water levels could reach one meter by 2100. Here, a billion fewer people will live than ten meters above sea level, which will leave them highly exposed to flooding.

Promoting the adaptation of cities to rising water levels, through an international network of mayors, scientists and experts: that is the ambitious goal of the Sea’Ties program. Together with her colleagues from the Ocean Climate Platform, Professor Françoise Gaill (CNRS) took the floor to announce, on the occasion of the international summit dedicated to the poles and glaciers (One Planet – Polar Summit, Paris, November 8-10, 2023), the first results of this initiative.

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On this crucial topic of adaptation, but also on the exploration of deep ecosystems of which it is one of the pioneers, GEO collected the testimonies of the French oceanographer for an episode of Vox, which you can see above.

Undersea voyage

In the 1980s, you were among the first researchers to investigate underwater hydrothermal vents or “black smokers.” Can you tell us something about the atmosphere, your feelings and what you saw? ?

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Françoise Gaill: I would say there were two moments. The first time I dived was with the Cyana, an Ifremer dish in the Mediterranean [nom du sous-marin porté par le navire océanographique Jean Charcot, N.D.L.R]. We didn’t get far, but it was already beautiful – despite the presence of the first plastics we started seeing at least 30 meters away.

But the real diving I was able to experience took place in 1980-82, in the Pacific Ocean, with the Americans and the Alvin – a ‘real’ submarine that went to more than 6000 meters depth. We were then identified as “heroes” because you had to really want it to dive this way.

The day before they put you in the dish. They locked you up there and told you the worst that could happen to you. If you got out there and still wanted to dive, yes, you could dive the next day!

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The saucer, or submarine, is a sphere with a diameter of two meters that was placed in the water. At first we stayed a bit on the surface; it was about 30-35 degrees. And when we descended, the Americans played music at the top of their lungs that ‘excited’ you a bit and allowed you to go down without fear.

Then we saw phosphorescent events around us: it was life capable of luminescence [on parle alors de bioluminescence, N.D.L.R.]. Finally, if we were lucky, as we reached the bottom we turned on the spotlights – and that’s when we came across beautiful animals and ecosystems.

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When you conducted these initial explorations, were you aware that this would prove crucial to understanding our current environment?

Yes, I was definitely aware of it, because I felt like I was discovering something new – and that there were some of us who could do it. It was incredible: what we discovered was incomprehensible!

We had a theory called ‘stability’, which stated that there could be a certain number of different species because there was no pressure and the environment was considered stable. But here it was the exact opposite!

We found ourselves in a tumultuous, completely crazy environment, with its “black smokers” spewing not steam, but absolutely black liquid, and also gigantic animals, which at least seemed gigantic to us through the porthole. This contradicted everything we had heard before.

“Nothing happens in the depths,” we were told, and on the contrary, we observed an oasis of life, a riot of colors and an absolutely fantastic dynamic.

‘Black smoker’ landscape in the deep sea. Ifremer

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Ocean and climate

Are we really aware of the importance of the ocean against global warming, and of the role of the ocean for the climate?

No, I don’t think we have this consciousness. It is very difficult to obtain it, especially because of the spatial dimension of the ocean: two-thirds of the Earth’s surface. It is something beyond our reach in relation to our human frame of reference. However, when we look at the ocean’s place in climate, we understand that it regulates the ocean.

Without the ocean, the Earth’s surface would be completely “burnt” as it absorbs 90% of the energy resulting from greenhouse gas emissions. The heat absorbed by the ocean allows us to still live on the Earth’s surface.

Moreover, ocean circulation around the world depends on the temperature difference between the equator and the poles. If this difference becomes smaller, we think this circulation will slow down – even though we cannot model this exactly yet. This is something the IPCC is starting to anticipate.

In any case, this realization that we need a healthy ocean for a protected climate is something we emphasize through the Ocean Climate Platform. I think tomorrow we’ll also get the reminder that it takes 1,000 years for a drop of water to return to the same spot after circling the Earth. Let’s try to anticipate the coming generations!

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Adaptation to rising water levels

To fully understand the issues, can you provide some figures on rising water levels? ?

We have a certain amount of data that comes from both satellites and buoys that measure sea level. These two pieces of information allow us to estimate sea level rise at an average of three millimeters per year for twenty years.

But what’s happening is that it seems to be accelerating. If we take into account the melting of glaciers and the increase in the volume of the ocean expanding under the influence of temperature (which also contributes to this rise in sea level), by 2050 we will have a water rise of about 30 cm .

2050 is tomorrow! Ten years ago it was assumed that this would be reached by 30 cm by the end of the century.

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Can we imagine that in a few years, coastal towns in France will be under water, as we can see in other geographical areas?

It seems to me that the big cities anticipated this demand, like New York. However, what happened in New Orleans can make us think: it was still a metropolis and yet it suffered from a phenomenon of immersion.

In France, for example, there is Paris, which anticipated the risk of flooding by taking all measures to save buildings and works of art, especially when the water rises. On the other hand, medium-sized cities do not necessarily have the financial resources to equip themselves or find solutions. That is why they are objectives for the Sea’ties project.

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Can you tell us about the solutions proposed by Sea’ties, mentioning the methods implemented (or to be implemented) in the areas concerned?

I think, for example, of La Rochelle, a city with which we have worked a lot and which for various reasons had to focus on climate change – the University of La Rochelle was one of its research priorities.

With Sea’ties we have collaborated in an interdisciplinary way with all stakeholders, that is to say by bringing together not only physicists, chemists and biologists, but also geographers, anthropologists and sociologists… biodiversity in the city, heat released by urban activities, etc. This allows you to gain a global vision that ordinary citizens do not have.

Furthermore, everything Sea’ties has achieved shows that there is not just one solution – and that is what we must keep in mind.

Every place is unique and must therefore create its own solutions.

To keep hope

Facing warming waters, but also ocean acidification, overfishing… What keeps you hopeful about saving the ocean?

First, I think that the ocean is characterized by a temporality that is that of “long time.” It is therefore now that we must act, and I believe that the human species is capable of taking its destiny into its own hands and planning this action. In any case, this is a hypothesis on my part, which also makes me think that we should think about this strategy for tomorrow.

The other is the (mis)knowledge we have about the oceans, weighed by our future discoveries. We have only mapped 5% of the seabed and we only know the first 700 meters from the surface. In other words, there are internal dynamics of the ocean that are not yet understood, nor learned, nor transferable. Around Antarctica, the Southern Ocean is a mystery. You must go there to unlock its secrets!

On the same subject:

⋙ Biodiversity: how can we protect our oceans?

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