If greenhouse gas emissions are not reduced, new research suggests that essential coastal mangrove ecosystems likely will not survive worst-case scenario sea-level rise expected by 2050.
Found in the warm, shallow waters of the planet’s tropical and subtropical regions, more than 80 species of mangrove trees provide essential habitat for fish and endangered species like manatees. Mangrove trees are characterized by their dense webbing of roots that provide stabilization to coastlines, thereby reducing erosion from storms, currents, waves, and tides, according to the National Oceanic and Atmospheric Administration. Though the ornate habitat also sees some of the highest rates of carbon sequestration, little is known about how mangrove trees will respond to rising waters, largely due to a lack of long-term observational data.
To fill this scientific hole, a team of international researchers turned to the paleorecord to estimate the likelihood that mangrove forests will survive projected sea-level rise. An analysis of sediment data from the last 10,000 years from across 78 locations around the world – from Sumatra and the Caribbean to Northern Australia and Central America – revealed how carbon was stored and expanded during the final stages of the Holocene deglaciation. It was during this period near the end of the last Ice Age that there were more dynamic rates of sea-level rise, providing insight into how mangroves respond to such environmental changes.
Mangroves were deemed more likely to survive when sea level rise was less than 5 millimeters (0.2 inches) each year, which is near the current projection for low-emission scenarios. When rates exceeded 6 millimeters annually – a closer estimate to high-emission scenarios by 2050 – mangroves were likely to stop growing. In some shallow reef settings, that limit was as low as 5 millimeters per year.
"Under high-emissions scenarios, rates of sea-level rise on many tropical coastlines will exceed 7 millimeters per year, the rate at which we concluded there's a 3.5 percent probability mangroves can sustain growth," said study co-author and post-doctoral scientist Erica Ashe in a statement. "The loss of these mangrove ecosystems could result in increased carbon dioxide in the atmosphere and fewer vital buffers against storm surges in the long run."
Under current climate conditions, the researchers anticipate that such thresholds will be surpassed in the next three decades. Altogether, the team notes the importance of mitigating rapid sea-level rise and supporting global coastal climate change adaptation measures.