The ability to halt the release of microplastics into the world’s oceans will not solve the current crisis scientists have warned.

Halting new marine plastic inputs by 2050 is the core objective of the Osaka Blue Ocean Vision, which was shared and endorsed alongside the G20 Implementation Framework for Actions on Marine Plastic Litter.

However, stopping new plastic inputs will not remove existing marine debris, which can gradually fragment into microplastics that are difficult and costly to remove. Therefore, source reduction must be accompanied by clean-up of legacy plastic debris.

Professor Takuro Uehara from the College of Policy Science, Ritsumeikan University, Japan, Dr. Mateo Cordier of Université de Versailles-Saint-Quentin-en-Yvelines—Université Paris-Saclay, France, and. Laurent Lebreton of The Ocean Clean-up, The Netherlands, have developed a system dynamics model examining the physical and economic effort required to address initially buoyant marine plastic debris by 2050.

“The framework is designed to look at marine plastic pollution as a dynamic problem rather than a one-time cleanup challenge.” added Uehara. “By linking plastic inputs, the movement and breakdown of debris, clean-up timing and location, and the associated costs, it allows to explore which combinations of prevention and clean-up could be both environmentally effective and economically realistic. This provides a basis for more informed decisions about where and when clean-up efforts should be prioritised.”

The model followed the transport and degradation of macroplastics and their breakdown into microplastics across shorelines, coastal waters, and offshore areas. The researchers tested seven scenarios combining different pathways for reducing plastic inputs with different approaches to clean-up. In scenarios aimed at stopping plastic at its source, inputs were progressively reduced from 2026 until reaching zero by 2050. The model then compared various clean-up strategies to assess how the timing and intensity of these measures could influence the amount of plastic remaining in the ocean.

The team’s research showed that halting plastic inputs by 2050 could reduce the cumulative amount of plastic entering the ocean between 1950 and 2050 by 51.4% compared with the business-as-usual (BAU) scenario. However, stopping new inputs alone did not resolve the legacy of plastic already in the ocean. Without clean-up, microplastics were projected to make up 58.4% of accumulated plastic by 2050.

Clean-up without source reduction was also insufficient, the team added. For example, delayed clean-up under BAU resulted in approximately 10,319 kt of microplastics remaining in the ocean by 2050, compared with 10,146 kt under source reduction combined with delayed clean-up. All clean-up scenarios focused on removing macroplastics, leaving microplastics unaddressed. Among the full-clean-up strategies combined with source reduction, accelerated clean-up resulted in the lowest amount of plastic debris remaining by 2050. Under Scenario 4, which combined source reduction with delayed clean-up, approximately 10,168 kt of plastic remained by 2050. This decreased to 8,824 kt under constant clean-up and 7,312 kt under accelerated clean-up.

The findings highlight the importance of timing when initiating marine plastic clean-ups. Accelerating the removal of legacy plastic while their concentrations are still high is the most ecologically effective strategy. Early intervention prevents these larger items from fragmenting into microplastics, which current large-scale technologies fail to recover efficiently.

However, faster clean-up is associated with substantially higher costs. Delaying full clean-up costs an estimated average of €1 billion annually, whereas accelerating clean-up between 2026 and 2050 drives costs up to €3.4 billion per year. Offshore operations are more expensive: compared to clean-up operations at the shorelines. Furthermore, as clean-up operations deplete plastic concentrations, the unit cost increases over time.

Uehara added: “The scale of marine pollution demands more than just better clean-up strategies. Relying on massive recovery efforts to balance out unchecked plastic waste is a structurally unsustainable solution.”