Symposium: Marine pollution and climate change

Summary

Report of the round table on marine pollution and climate change held at the Symposium of European Marine Academies in Marseille in March 2025. Moderated by Hervé Baudu and Christophe Enault, it brought together Zhen Sun on the advisory opinion of the International Tribunal for the Law of the Sea, François Galgani on an overview of marine pollution and Christophe Maes on the dispersal of plastics in the ocean.

General information

• Event title: 3rd theme of the symposium: Marine pollution and climate change.
• Organiser: Académie de marine.
• Date: 25 and 26 March 2025.
• Venue: Marseille, École nationale supérieure maritime (ENSM) and CMA CGM’s TANGRAM Center.
• Moderators: Hervé BAUDU, Christophe ENAULT.
• Theme: The link between marine pollution and climate change, approached from the angle of international law, the overall state of pollution (hydrocarbons, chemicals, eutrophication) and a focus on plastic pollution (dispersal, impacts, solutions).
• Summary written by: Deep Blue

Presentation of the symposium

This round table, devoted to marine pollution and climate change, is the third theme of a broader symposium. Moderated successively by Hervé Baudu, professor at the École Nationale Supérieure Maritime (ENSM), and then by Christophe Enault, deputy to the director of the sea for Corsica, it aims to shed light on this vast subject by combining legal and scientific approaches.

The session is organised around the presentations of three main experts. The first, legal in nature, analyses a recent advisory opinion of the International Tribunal for the Law of the Sea on the obligations of States in the face of climate change. The next two, scientific in nature, provide an overview of marine pollution before focusing on the issue of plastic waste, its dispersal mechanisms, its impacts on ecosystems and response strategies.

The aim is to leave significant time for exchanges with the audience after the experts’ presentations.

Participants

Moderators

• Hervé BAUDU — Professeur en chef de première classe de l’enseignement maritime (senior professor of maritime education), lecturer in nautical sciences and oceanology, École Nationale Supérieure Maritime (ENSM).
• Christophe ENAULT — Deputy to the director of the sea for Corsica.

Speakers

• Zhen SUN — Associate researcher at the WMU-Sasakawa Global Ocean Institute, World Maritime University (Malmö, Sweden).
• François GALGANI — Oceanographer, researcher and project leader at the French Research Institute for Exploitation of the Sea (Ifremer), specialist in marine ecotoxicology.
• Christophe MAES — Physical oceanographer at the French National Research Institute for Sustainable Development (IRD), Laboratory of Physical and Spatial Oceanography (LOPS).

Participants in the discussion

• François-Charles (surname not specified) — IRCE (general-interest European think tank).
• Commander Leduf — Marseille Naval Fire Battalion.
• Laurent Mortier — Institut Polytechnique de Paris.
• A speaker — European Parliament.
• Gilles Bessero — Académie de marine.

Report of the presentations

Introduction by the moderator

Presentation by Hervé BAUDU, professeur en chef de première classe de l’enseignement maritime

Hervé Baudu opens the session by stressing the breadth of the theme “Climate change and pollution”. He explains that the round table will focus on three areas thanks to the expertise of the invited speakers: Professor Zhen Sun, Dr François Galgani and Dr Christophe Maes. The session will take place in three stages: a legal analysis of an advisory opinion of the International Tribunal for the Law of the Sea (ITLOS), a general overview of marine pollution, then a focus on plastic pollution, before a question period with the audience.

Mr Baudu stresses that the consequences of climate disruption and pollution are daily realities for seafarers. He mentions the commitment of the maritime community to minimising its impact, notably through the decarbonisation of shipping and ports. He highlights innovative French initiatives such as sail-powered transport (Neoline, Zéphyr et Borée), hydrogen propulsion (Energy Observer) and the management of land-based plastic waste (Plastic Odyssey).

Finally, he illustrates the issues with the example of the polar regions. The disappearance of Arctic sea ice could open new shipping routes before 2050, increasing the risks of pollution (black carbon, noise pollution) in this sensitive ecosystem. These new risks call for stronger regulations, currently under discussion at the International Maritime Organization (IMO).

I. The ITLOS advisory opinion: towards greater State responsibility in the face of climate change

Presentation by Zhen SUN, researcher at the World Maritime University

Professor Zhen Sun presents the advisory opinion delivered by the International Tribunal for the Law of the Sea (ITLOS) on the responsibilities of States with regard to climate change. Her presentation seeks to establish the link between the law of the sea and climate law, to explain the content of this opinion and to analyse its scope.

A. The link between the Convention on the Law of the Sea and climate change

Professor Sun recalls that the United Nations Convention on the Law of the Sea (UNCLOS), negotiated in the 1970s, does not explicitly mention climate change. However, it lays down general obligations to protect and preserve the marine environment. UNCLOS is a “living document” that incorporates international rules developed later. This mechanism makes it possible to interpret its obligations in the light of more recent legal regimes on climate, such as the Paris Agreement. The central question is whether greenhouse gas (GHG) emissions can be qualified as “marine pollution”.

B. The origin and purpose of the ITLOS advisory opinion

The opinion was requested by the Commission of Small Island States on Climate Change and International Law (COSIS), led by Antigua and Barbuda and Tuvalu. These States, particularly vulnerable to the effects of climate change, seek to establish the legal consequences for the historically higher-emitting States. Although an advisory opinion is not binding, it clarifies the interpretation of the law. The two questions put to ITLOS sought to specify the particular obligations of States under UNCLOS to prevent pollution by GHGs and to protect the marine environment from their impacts.

C. The clarifications provided by the Tribunal

The Tribunal’s opinion, delivered on 21 May 2024, qualifies GHG emissions as marine pollution for the first time. This qualification triggers all the obligations of Part XII of UNCLOS on the protection of the environment.

The main conclusions are:

• 1. A stringent due diligence obligation: States have a specific obligation to take “all necessary measures” to control GHG emissions. This obligation of conduct (due diligence) is high, as the risks are considered serious.
• 2. A hierarchically higher obligation: Complying with the commitments of the Paris Agreement is not enough to satisfy the obligations of UNCLOS, which are considered more demanding.
• 3. Coverage of all sources of pollution: The obligation covers emissions from land-based sources, ships and the atmosphere.
• 4. Specific obligations of cooperation: Developed States have an obligation to assist developing countries, in particular small island States.
• 5. The obligation of environmental impact assessment: States must assess the impacts of any activity likely to affect the climate.

In conclusion, this opinion, strongly grounded in science, considerably strengthens the legal obligations of States on climate matters by anchoring them in UNCLOS.

II. Marine pollution: scientific diagnoses, impacts and avenues for action

Presentation by François GALGANI, oceanographer, researcher at Ifremer

François Galgani, a researcher at Ifremer, offers an overview of the main categories of marine pollution, emphasising the plurality of origins, the diversity of scales and the interplay between scientific diagnoses, legal frameworks and management strategies.

A. Mapping marine pollution

The speaker sets out a typology of pollution: hydrocarbons, trace metals, organic pollutants, nutrients and eutrophication, and finally plastic waste. He stresses that while chemical pollution is generally regional or local, greenhouse gas emissions and plastics pose global problems.

• Hydrocarbons and trace metals: The frequency of oil spills has decreased, but chronic inputs (atmospheric, industrial discharges) remain significant. For metals, it is complex to distinguish anthropogenic sources (factories, mines) from natural sources (volcanism). Better control and knowledge are observed for these two categories.
• Organic pollutants: Antifouling products such as tributyltin (TBT), although banned in many countries, persist and have severe effects (e.g. sex change in gastropods). Pesticides and insecticides have localised impacts, notably in the Mediterranean.
• Nutrients and eutrophication: Massive inputs of nitrates and phosphates cause algal blooms and “dead zones”. Nearly 500 areas are severely affected worldwide, but the phenomenon can be reversed through local action, such as that tested in the Baltic Sea under the European Commission’s Ocean Mission.

B. Focus on plastic pollution

Plastic pollution accounts for 80% of marine litter, with multiple sources: land-based (management shortfalls, river inputs), shipping and fishing (10–15%). Extreme events such as the tsunami in Japan can also return massive quantities of waste to the sea. Ocean currents carry this debris everywhere, including to the polar regions.

The impacts are multiple:

• Ingestion and entanglement for marine wildlife (birds, turtles).
• Health concerns for humans, linked to nanoparticles capable of crossing intestinal barriers.
• Socio-economic costs of clean-up, estimated at 10 billion euros/dollars per year.

C. From solutions to global monitoring

Faced with this challenge, François Galgani outlines several avenues:

• 1. Recycling and new materials: Research is under way on fully recyclable plastics.
• 2. Targeted clean-up: Recovering fishing nets has economic value, unlike collecting low-value waste.
• 3. Institutional mobilisation: Europe is a driving force, with directives (MSFD, port reception facilities) and massive investment in research. The ongoing negotiations for an international plastics treaty are crucial.

To conclude, he argues for a global monitoring system, on the European model, to measure the effectiveness of the policies implemented, illustrating his point with an Ifremer video showing a carpet of waste at a depth of 2,200 metres.

III. The dispersal of plastic in the ocean: modelling, impacts and prospects

Presentation by Christophe MAES, physical oceanographer, IRD and LOPS

After an introduction by Christophe Enault, Christophe Maes, of the IRD, places awareness of plastic pollution in historical perspective, recalling its discovery in the Sargasso Sea as early as 1972, and presents what modelling contributes to understanding its fate.

A. Global dispersal: the role of ocean gyres

Plastics, mainly from the continents, accumulate in five large zones at the centre of the subtropical gyres. This phenomenon is reproduced by Lagrangian models that track virtual particles subject to currents. The accumulation is explained by the combination of winds and the Coriolis force (Ekman transport). The model reproduces the known zones (Great Pacific Garbage Patch) and reveals connections between ocean basins, although uncertainties remain in the southern hemisphere for lack of data.

B. A regional approach: the case of Indonesia

At a finer scale, in Indonesia, a high-resolution model shows that of the plastics coming from rivers, 60% wash up on local coasts, 30% leave the area for the Indian and Pacific Oceans, and only 10% remain at sea and disperse. These results, compiled in an atlas, help the Indonesian authorities to identify beaching zones and contributing rivers.

C. Interactions with ecosystems and the carbon cycle

Research on plastics has led to unexpected discoveries, notably that cyclonic ocean eddies capture floating objects 24% more often than anticyclonic ones.

Beyond physics, models coupling oceanography and biogeochemistry (NEMO-PISCES) study the interactions with plankton. Zooplankton ingest microplastics, reducing grazing pressure on phytoplankton. Simulations indicate that this interaction could lead to a decrease in primary production and in carbon export to the seabed of nearly 4%. The speaker considers this magnitude “similar to what is happening in the current changing climate”, underlining its importance.

D. Uncertainties and optimising collection

Christophe Maes stresses the many remaining unknowns, notably on the ecotoxicology of plastic additives and the life cycle of debris. He presents a study optimising collection systems (of The Ocean Cleanup type) in the North Pacific. By targeting “hotspots” and convergence fronts, efficiency is maximised. He estimates the cost of collecting 100% of the floating waste in this zone at 4 billion euros over several years, considering the operation “not unfeasible” but recalling that the absolute priority remains reducing inputs at source.

IV. General discussion with the audience

The session continues with a series of questions and answers with the audience, moderated by Christophe Enault.

A. Questions on legislation, clean-up strategy and ocean currents

François-Charles (IRCE) asks the experts about the choice of a directive rather than a European law for plastics, about whether accumulation zones should be kept in order to locate them, and about the link between the drift of waste and the Gulf Stream.

• François Galgani explains that the regulation on fishing was adopted by a very large majority in Parliament and will be transposed. Regarding accumulation zones, he considers it unthinkable to leave them on the coasts for aesthetic reasons, but believes that cleaning the seabed is economically unrealistic.
• Christophe Maes confirms that plastic waste from Canada is found in Brittany, proving the transatlantic connection. A slowdown of the Gulf Stream would not stop this transport, as eddies would still play their role.

B. Chemical pollution and the impact of climate disasters

Commander Leduf (Marseille Naval Fire Battalion) raises concerns about strategies to combat soluble chemical pollution and the massive land-based pollution generated by extreme climate events (cyclones, floods).

• François Galgani explains that for the tens of thousands of chemical molecules, the only viable solution is prevention at source, through “zero pollution” policies and the widespread use of tertiary wastewater treatment, which remains “wishful thinking”. He confirms that climate disruption generates massive plastic pollution.
• Christophe Maes adds that these extreme events could be incorporated into dispersal forecasting models.

C. Systematic monitoring of pollution

Laurent Mortier (Institut Polytechnique de Paris) questions the strategy for observing plastics: systematic high-frequency monitoring or periodic sampling?

• François Galgani stresses the challenge of sample representativeness and the importance of acquiring massive amounts of data. Satellite detection, which now identifies plastic slicks, is a promising avenue for obtaining a global picture.
• Christophe Maes mentions projects for monitoring by AI and cameras on merchant ships, alongside existing physico-chemical observation networks.

D. Political and legal issues of the plastics treaty and the law of the sea

A participant from the European Parliament, after praising the legislative work carried out (Starfish mission, “zero waste” objective), asks the scientists for their recommendations to move forward the negotiations on the plastics treaty, whose difficulties she notes.

• François Galgani, who took part in the preparatory work, explains that the treaty has become global, covering the entire life cycle of plastic, which creates political and economic tensions between producing and non-producing countries. Since responsibility is shared (consumers, fishing, industry), he considers it a priority to obtain a framework agreement with reasonable objectives.

Gilles Bessero (Académie de marine) asks whether the ITLOS opinion on climate change is likely to influence the International Court of Justice (ICJ), which has also been seised.

• Zhen Sun explains that the ITLOS opinion is limited to UNCLOS and the marine environment. The request to the ICJ is broader, covering general international law, including human rights. The ICJ’s opinion will therefore have a more general scope, but it is hoped that it will confirm that climate change also falls within marine pollution, making the two opinions complementary.

General conclusion

This round table highlighted the growing interconnection between the issues of marine pollution and climate change. A clear consensus emerged on the need to act at source, whether for plastics, chemicals or GHG emissions, prevention being the only viable long-term strategy.

On the legal front, Zhen Sun’s presentation showed how the law of the sea is evolving to impose stricter climate obligations on States, paving the way for potential litigation over responsibilities.

On the scientific front, the presentations by François Galgani and Christophe Maes provided a comprehensive overview of pollution. While control is improving for hydrocarbons and certain metals, plastics and eutrophication pose growing challenges. Modelling appears to be a crucial tool for understanding the dispersal of pollutants and optimising interventions. However, all the speakers stressed the gaps in knowledge, notably in ecotoxicology and on the impacts of microplastics on biogeochemical cycles, and called for stronger data acquisition through global observation systems.

The debates showed that while technical clean-up solutions exist and can be optimised, their cost and effectiveness at large scale remain open to question in the face of continuous pollution flows. The final discussion confirmed that environmental issues are inseparable from political and economic dynamics and from State sovereignty, as illustrated by the difficulties in the negotiations on the international plastics treaty. The main question that remains open is the capacity of the international community to translate scientific urgency into binding and effective political commitments.

Bibliographic information

Type

Conference

Date

March 2025

Author

Deep Blue Foundation

Editor

Deep Blue Foundation

Study Centres

ONS · DMGO

Original language

French

Original document

PDF, 10 pages

Full text

Transcription of the original document

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