Can rising seas turn mangroves into carbon sources?

Rising seas could flip mangroves from carbon sinks to sources

Mangrove forests have long been viewed as climate “heroes” because they store carbon in waterlogged soils and keep carbon out of the atmosphere. But new research warns that rising sea levels may undermine that role.

The core concern is that as coastlines rise, mangroves can become less able to keep pace with changing conditions. If saltwater intrusion, flooding frequency, and oxygen levels shift faster than mangroves can adapt, the soils where mangroves normally lock away carbon may start to behave differently. Instead of holding on to stored organic matter indefinitely, mangrove sediments could become more prone to decomposition processes that release carbon back into the environment.

That matters because mangroves sit at the intersection of climate and biodiversity: they protect shorelines while providing habitat for many species. If sea-level rise turns them from net carbon stores into net emitters, the climate benefits of coastal wetland conservation could be smaller than expected.

For climate planning, the takeaway is straightforward:

• Coastal protection and carbon storage are linked outcomes, not separate projects.
• Restoration and protection strategies may need to consider sea-level trajectories and local conditions that determine whether mangroves can survive and keep accumulating carbon.
• “Nature-based solutions” must be evaluated under future climate dynamics, not just under today’s baseline.

Overall, the research reframes mangroves from an automatically secure climate solution to a system that could change roles as environmental stress increases. Protecting mangroves may still help, but their carbon performance may require more adaptive management than in the past.