A specialist in tropical islands and lead author of the ‘Small Islands’ chapter in the latest IPCC report, Virginie Duvat met with stakeholders in the French overseas territories who are committed to protecting coastal ecosystems. With her ‘ADAPTOM’ project, the CNRS researcher is highlighting nature-based solutions, which she believes are far more effective than heavy defence (dykes, protective walls) in combating the risk of marine submersion.
By Marion Durand
Cover photo : Virginie Duvat © Marion Durand
Restoring native coastal plant formations in developed areas, here on the Club Med des Boucaniers site in Martinique. Julien Masinsky
Virginie Duvat is a professor of geography at the University of La Rochelle (France) and a researcher at the Littoral, environnement et sociétés (LIENSs) laboratory of the CNRS (National Centre for Scientific Research). As holder of a Senior Innovation Chair at the Institut Universitaire de France (2023-2028), this specialist in tropical islands is interested in the nature-based solutions deployed in overseas France to tackle climate change.
As part of the ADAPTOM project, which will run from 2022 to 2025, Virginie Duvat has met a number of stakeholders in the French West Indies, the Pacific and the Indian Ocean who have set up judicious projects to preserve coastal ecosystems and deal with the risk of marine submersion. Virginie Duvat is also the main author of the ‘Small Islands’ chapter of the 5th and 6th IPCC (Intergovernmental Panel on Climate Change) reports.
According to the latest IPCC report, ocean levels have been rising by 3.7 millimetres every year for the past decade (2006-2018). Why is this figure so worrying?
If we stopped producing greenhouse gases, the global ocean would continue to rise for centuries. We can no longer regain control over this physical phenomenon. Sea levels are rising at an average rate of 3.7 millimetres a year, but this is set to increase to 4, 4.5 and then 5 millimetres in the near future. This is also very worrying because climate pressure factors are not limited to rising sea levels. We are seeing an accumulation of climate pressures that are being exerted jointly on all regions of the world. In 96% of regions, more than ten climatic parameters are changing, including winds, rainfall, seasonality, rainfall distribution, etc. We are entering a new era of combined climatic events, and the time elapsing between two successive events is becoming shorter. Human societies and ecosystems will have less and less time to recover.
Does this rise in sea level differ from one part of the world to another?
Yes, it varies greatly depending on the area of the globe and the configuration of the ocean basins. In the Pacific, the planet’s largest ocean basin, sea levels are rising much faster in the western part. In Tuvalu, the sea is rising two and a half times faster than in French Polynesia. This variability also depends on plate tectonics, since the rise in sea level also depends on the behaviour of the continents, some sinking, others rising. Take the case of Mayotte where, following the formation of a new underwater volcano in 2018, a tectonic rise in sea level of around 20 cm was observed, in addition to the rise linked to global warming.
Restoration of mangroves by the Hô-üt association in the Touho commune in New Caledonia © Virginie Duvat
How will rising sea levels affect France between now and 2050?
Most of the French overseas territories are experiencing a rise in sea level close to the global average. But we do know that there are hot spots, such as the Jarry industrial zone in Pointe-à-Pitre (Guadeloupe), where there is natural subsidence because the area was developed on marshy mudflats. We also know that the situation in Nouméa, New Caledonia, will be critical over the course of this century, as it will be in the bay of Fort-de-France in Martinique.
You have worked on ‘atolls’, low-lying coral islands that are ring-shaped and have a lagoon, often shallow, at their centre. What are their particular characteristics in the face of the climate emergency?
Images of the Maldives, Tuvalu, Kiribati or the Tuamotus spring to mind, because France has the largest group of atolls in the world, with 77 in French Polynesia. These atoll coral islands are very small, low-lying (most have a maximum height of 4 metres) and relatively mobile. Following major cyclones, these islands can move as their centre of gravity shifts due to the transfer of sedimentary material from the coasts exposed to cyclonic waves to the rest of the island. This means that their perimeter and geometry are constantly reshaped by marine and climatic forces. The populations of these atolls depend heavily on ocean resources to meet their needs, so the future of the ocean in the context of climate change will really determine the ability of the inhabitants to continue to live on these islands and maintain their culture and identity.
Site visit to Guadeloupe to share experiences of nature-based coastal adaptation solutions, as part of the ADAPTOM project © Fanny Rubia
You are leading the ADAPTOM project, the aim of which is to assess the potential of nature-based solutions for reducing coastal risks that have been deployed in overseas France. Why did you choose these territories?
Apart from the fact that I am a specialist in tropical islands, we have a lower level of knowledge of overseas France than metropolitan France. There’s often a tendency to think that the French overseas territories are lagging behind because they are less developed territories, where decolonisation is more or less complete. With ADAPTOM, I wanted to take stock of the experiments being carried out there to reduce coastal risks in order to draw some useful lessons. We have identified 25 experiments, most of which are ecosystem restoration projects, with the addition of a site management component. Most of the projects concern mangroves and coastal vegetation.
How does coastal vegetation help to contain the risk of marine submersion?
The nature-based solutions approach is based on the use of an ecosystem service known as the ‘ coastal protection service’. It leads us to recognise that marine and coastal ecosystems have the capacity to attenuate waves and produce or fix sediments. This is fundamental if these ecosystems are to truly play their role as a buffer zone against extreme events. When a cyclonic wave arrives on the coast, it is first slowed down by the coral reefs. The roughness of a healthy reef reduces the speed of the wave, its height and ultimately its corrosive and devastating impact on the coast. The wave then passes through the seagrass beds, then through the mangroves and coastal vegetation, which also act as shock absorbers.
It is therefore essential to maintain vegetation on beaches…
Exactly. It’s even extremely important to preserve what we call the ecosystem continuum. Today, many projects focus on a single ecosystem, even though they all work together. If one is damaged, the health of the other will deteriorate rapidly. Today, the challenge is to move from projects focused on a particular ecosystem to projects that target the continuum.
Restoration of native coastal vegetation by the Centre for the Study and Discovery of Marine Turtles on Réunion Island © Virginie Duvat
Why is it important to implement these adaptation measures now?
Climate change is happening all over the world. Action is urgently needed because adaptation policies are lagging behind the impacts of climate change. We have not been able to deploy adaptation efforts that are commensurate with the impacts already felt, and even less so to cope with the foreseeable impacts of the decades to come. This is what we call the adaptation deficit. So we urgently need to get moving to avoid a staggering increase in the impacts of climate change.
What do you think are the priority measures to be put in place to reduce coastal risks in the context of climate change?
In France, we are in the process of recognising the poorly adaptive nature of heavy defence: the construction of dykes, protective walls and riprap. Today, the government is acknowledging the unsustainable nature of this type of defence and is supporting the transition to nature-based solutions on the one hand, and relocation on the other, which involves moving people, infrastructure and economic activities inland to safer areas. We’re going to move from coastalisation to ‘delittorialisation’, and that’s quite a turning point in human history. In my opinion, it is urgent to embark on these bifurcations, which require us to rethink and change our paradigm. We have to recognise that we can’t resist natural processes, we can’t take control, we have to step back. These major changes in modes of governance require the involvement of all the stakeholders, because this revolution in the territories must involve all the people concerned and avoid leaving anyone out in the cold. This is extremely important, because the climate issue is also a question of climate justice.