After studying more than 1,500 coastal ecosystems, researchers say they will sink if we allow global warming to exceed 2°C.

Much of the world’s natural coastline is protected by living habitats, most notably the warm-water mangroves and tidal marshes near the poles. These ecosystems support fisheries and wildlife, absorb the impact of the waves and clean up pollutants. But these vital services are threatened by global warming and rising sea levels.

Recent research has shown that wetlands can respond to rising sea levels by building up their root systems, drawing carbon dioxide from the atmosphere in the process. It is the growing recognition of the potential for this ‘blue’ carbon capture that is driving mangrove and tidal marsh restoration projects.

Although the resilience of these ecosystems is impressive, it is not without limits. The delimitation of the upper limits of mangroves and swamps under accelerating sea level rise is a topic of great interest and debate.

our new research, Published in the journal nature, analyzes the vulnerability of mangroves, swamps and atolls to sea level rise. The results underscore the critical importance of keeping global warming within 2 degrees of a pre-industrial baseline.

What have we done

We have gathered all available evidence on how mangroves, tidal marshes and atolls are responding to sea level rise. which included:

• Delving into the geological record to study how coastal systems responded to sea level rise in the past, after the last Ice Age
• Benefit from a global network of Survey criteria In mangroves and tidal swamps
• Satellite image analysis of changes in the extent of wetlands and atolls at varying rates of sea level rise.

In all, our international team has assessed 190 mangroves, 477 tidal marshes, and 872 coral reef islands around the world.

We then used computer modeling to determine the vulnerability of these coastal ecosystems to rapid sea level rise under projected warming scenarios.

What we found

Mangroves, tidal swamps and coral reefs can adapt to lower rates of sea level rise. remain stable and healthy.

We found that most tidal swamps and mangroves are keeping pace with current rates of sea level rise, by about 2-4 mm per year. Atolls also appear stable under these conditions.

In some locations, the land is sinking, so the relative rate of sea level rise is greater. This number may be double, 2-4 mm or more, compared to expected rates in light of future climate change. In these cases, we found that the swamps failed to keep pace with sea level rise. They sink slowly and, in some cases, separate. What’s more, these are the same rates of sea level rise at which swamps and mangroves are engulfed in the geologic record.

These cases give us a glimpse into the future in a warming world.

So, if the rate of sea level rise doubles to 7 or 8 millimeters per year, it becomes “very likely” (90% chance) that mangroves and tidal marshes will not keep up, and “likely” (67% chance) that atolls You won’t be able to keep up. They will undergo rapid changes. These rates will be reached when the 2.0°C warming threshold is exceeded.

Even at low rates of sea level rise, we would have between 1.5°C and 2.0°C warming (4 or 5 mm per year), and likely widespread loss of mangroves and tidal marshes.

Tidal marshes are less exposed to rates of sea level rise than mangroves because they occur in areas where land rises, which reduces the relative rate of sea level rise.

Let’s give coastal ecosystems a fighting chance

We know that mangroves and tidal marshes have survived rapid sea-level rise before, at even higher rates than would be expected under extreme climate change.

They will not have time to build up root systems or trap sediment to stay in place, so they will seek higher ground by turning inland to the newly flooded coastal lowlands.

But this time, it will compete with other uses of the land, and become increasingly trapped behind coastal dikes and hard barriers like roads and buildings.

If global temperature rise is limited to 2°C, coastal ecosystems have a chance to fight back. But if that threshold is crossed, they will need more help.

Intervention is needed to enable the retreat of mangroves and tidal marshes across our coastal landscapes. There is a role for governments in defining pathways of decline, controlling coastal development, and expanding coastal nature reserves to higher ground.

The future of the world’s live coasters is in our hands. And if we work to restore mangroves and tidal marshes to their former size, they can help us tackle climate change.

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