Planetary boundaries / equatorial belt & vulnerabilities / marine heatwaves / sea level rise / ocean acidification / mitigation vs adaptation / climate justice / North–South equity / climate migration / blue carbon (mangroves, salt marshes, Posidonia seagrass meadows) / ecological restoration (grafting/genotype banks) / dynamic conservation (ecotypes/assisted migration) / MCDR (Marine Carbon Dioxide Removal) / ocean alkalinity (uncertain impacts) / GMOs/NBTs (varietal selection under water/temperature stress) / coral resilience (mutation/selection) / emission sources: transport (urban vs rural), buildings (thermal renovation), agriculture (N₂O, CH₄), industry (steel, cement), energy (France/EU specificities) / ecosystem services / carbon markets & biodiversity credits / debt-for-nature swaps / double materiality / participatory science / co-production of public policies / regenerative economy / transdisciplinarity & multi-disciplinary training.

Based on the contributions of Nathalie HILMI (environmental economics, Scientific Center of Monaco), Robin DEGRON (Plan Bleu – UNEP Mediterranean) and the moderation of Thomas EGLI (Objectif Sciences International), this article links physical diagnostics (marine heatwaves, sea level rise, acidification), socio-economic challenges (transport, buildings, agriculture, industry, energy), and pathways for action combining nature-based solutions, cautious technological innovations, financial levers, and participatory science. The central focus is on “operational” transdisciplinarity and assertiveness in arbitration between mitigation and adaptation, with strong requirements for climate justice, North–South equity, and ecological integrity.

The content below aims to serve as a methodological resource for readers.

"Transdisciplinarity is not a slogan: it is a method to clarify trade-offs between mitigation and adaptation as close as possible to coastal and urban areas." – Nathalie HILMI

"In the Mediterranean basin, pressure is accelerating: marine heatwaves, sea level rise, ocean acidification, and biodiversity stress demand co-constructed and governed responses." – Robin DEGRO

"Participatory science shifts the scale of what’s possible: it connects citizens, researchers, businesses, and public authorities to co-produce public policies and evidence of impact." – Thomas EGLI

1. Context, corpus, and objectives

The discussion takes place during the official opening of the #ParticipatoryScience Hackathon for the #Ocean, in an interactive and multilingual format, and draws on the recordings and transcriptions as its primary source material. The scientific objective of this article is twofold: i) to synthesize robust findings on ecosystem states and emission sources; ii) to formulate a methodical, measurable, and replicable roadmap linking biophysical evidence, economic feasibility, governance, and citizen engagement.

2. Theoretical framework and disciplinary scope

The stated approach is strictly transdisciplinary: it goes beyond disciplinary juxtaposition to integrate “value interfaces” across natural sciences, engineering, economics, law, public policy, and social sciences.

The scope encompasses oceanography, climatology and climate science; marine ecology and conservation biology; forestry and terrestrial ecology; urban planning and urban resilience (green islands); transport planning (tramways, urban/rural contrasts) and building thermal performance (thermal renovation); coastal engineering and ecological restoration (coral reefs, Posidonia); genetics and biotechnologies (NBTs, GMOs); materials engineering (alternatives to concrete) and industrial processes (steel, cement); energy (transport electrification, nuclear specificities in France/EU); agronomy, agroecology, permaculture, and food security; environmental economics, ecosystem service valuation, carbon markets and biodiversity credits, debt-for-nature swaps, finance/risk management (double materiality, European directive); climate/adaptation policy and international law; climate justice and North–South equity; sociology, anthropology (endangered cultures, migration), journalism/communication and participatory science as a bridge between stakeholders.

3. Warning signs and consolidated diagnostics

In the Mediterranean basin and beyond, the physical trajectory confirms that we have already crossed several planetary boundaries: intense and repeated marine heatwaves, sea level rise, and ocean acidification with impacts on coral reefs and Posidonia oceanica seagrass meadows (blue carbon). On land, forest mortality is increasing, raising the issue of species selection under future climate. In the equatorial belt & vulnerabilities, cumulative vulnerability combines climate, biodiversity, food security, and climate migration.

The main emission sources (France/EU case) stem from transport (significant urban/rural contrasts and purchasing power constraints), buildings (priority on renovation), and agriculture (N₂O from nitrogen inputs, CH₄ from livestock), with a more nuanced role for industry (steel, cement) and energy (energy mix and the role of nuclear). These dynamics must be interpreted through socio-spatial trajectories (urban tramways vs car dependence in low-density areas) and recent political lessons on acceptability (e.g., "carbon tax" shock).

4. From evidence to solutions: nature, technology, trade-offs

Nature-based solutions (NBS) emerge as a “baseline”: protecting/restoring blue carbon stocks (mangroves, salt marshes, Posidonia seagrass), ecological restoration of coral reefs, and dynamic conservation (use of ecotypes, assisted migration, grafting, genotype banks) along coastal regions. Governance must clarify scale and funding limits and integrate positive externalities (coastal protection, biodiversity, health, education).

On the technological side, MCDR (Marine Carbon Dioxide Removal) components and ocean alkalinity are under study but require robust ecological assessments and methodological caution due to uncertain impacts. Engineering points toward a “green-grey” coastal engineering and materials engineering favoring alternatives to concrete and efficiency in industrial processes. GMO/NBT trajectories are also examined through the lens of risk/benefit/acceptability, both for agriculture and coral resilience.

5. Economic levers, finance, and risk management

Translating ecological benefits into decision-making language requires ecosystem service valuation and well-governed financing mechanisms: carbon markets and biodiversity credits, debt-for-nature swaps, insurance instruments, and finance/risk management frameworks aligned with double materiality (as per the EU directive). These levers should support a regenerative economy where flows restore more than they degrade, not merely displace externalities.

6. Justice, equity, and climate geopolitics

Demanding North–South equity and climate justice means acknowledging differentiated responsibilities, financing adaptation where vulnerability is greatest, and avoiding neo-colonialism in technical, normative, or financial architectures. Addressing climate migration must inform planning, diplomacy, and cooperation — beyond just humanitarian responses.

7. Social mobilization, participatory science, and scaling

Participatory science is presented as a “scale accelerator” able to connect citizens, scientists, companies, and authorities, to co-produce public policies and evidence of impact, and to “pierce through” decision-makers’ awareness via direct involvement. Education and journalism/communication are needed for accountability, while companies and local authorities are urged to act as co-actors rather than mere funders.

8. Operational transdisciplinarity and project governance

Making transdisciplinarity operational requires multi-disciplinary teams, role clarity, a defined acceptable complexity threshold, decision traceability, and shared impact metrics. Recommended tools include a mitigation vs adaptation trade-off canvas, ecosystem service valuation matrices, and double materiality guides for projects and portfolios.

9. Case studies and application scenarios

Posidonia, ecotypes, and dynamic conservation — Restoring Mediterranean seagrass meadows benefits from using ecotypes more tolerant to high temperatures (East→West transfers), anticipating thermal regime shifts: this illustrates conservation as a dynamic process, not mere preservation.

Corals and biotechnological trajectories — Recent work shows extinction risks can be reduced via combined strategies of selection, directed mutation, and in situ ecological engineering — provided that risk assessment and acceptability protocols are applied cautiously. This mirrors broader debates on GMOs/NBTs in agriculture.

Hot city, livable city — In Mediterranean cities, urban resilience planning (green islands, shade, water) and thermal renovation reduce exposure to extremes and energy use; conversely, low-density areas remain car-dependent, raising questions of spatial equity and carbon instrument acceptability.

Materials and processes — Reducing the footprint of the steel and cement sectors requires not only process innovation but also alternatives to concrete when safety and cost allow, along with finance/insurance mechanisms aligned with technological risks.

10. Discussion: assertiveness, timeframes, and funding allocation

Assertive climate policy requires clarity on timeframes: radiative stabilization occurs over decades, while adaptation — a “front-line” issue in the Mediterranean — offers immediate damage reduction leverage. Financial flow reallocation remains a bottleneck: today, most climate funding is focused on mitigation, even as vulnerable regions primarily need adaptation; rebalancing via ecosystem services, biodiversity credits, and debt-for-nature swaps, backed by double materiality, aligns with a regenerative economy.

11. Roadmap for the Hackathon and beyond: principles, milestones, deliverables

Four key action principles are proposed: i) “evidence→policy” (protocols and indicators aligned with ecosystem services); ii) “local→systemic” (from site to coastline, neighborhood to watershed); iii) “co-governance” (industries and policymakers as co-actors); iv) “integrity” (caution on MCDR/alkalinity; safeguards against misguided financialization of nature).

Immediate milestones include: NBS teams (Posidonia, corals), finance/partnership track (carbon, biodiversity, debt-for-nature swaps), engineering track (coastal, materials), territory track (urban resilience, mitigation/adaptation trade-offs by geography), and agro-bio track (NBTs/GMOs vs agroecology/permaculture).

Deliverables: end-to-end project sheets, ecosystem service valuation models, pre-financing agreements, participatory science protocol, and media plan.

Conclusion

“Acting within planetary boundaries” is no longer a distant goal but a methodological imperative: linking the power of climate and ocean science to understandable economic instruments, cautious engineering, and shared governance that tackles both mitigation and adaptation simultaneously. Transdisciplinarity becomes a design and arbitration practice; assertiveness becomes an ethical demand — to state where we’re going, with whom, and how we measure what is truly restored. Participatory science, by broadening stakeholder involvement and data foundations, offers a chance to bridge the remaining scale gap between ambition and reality.