Coastal destruction speeds climate change

Posted: 30 March 2011

The destruction of coastal ecosystems such as mangroves, seagrasses and tidal marshes, which have a high carbon content, is leading to rapid and long-lasting emissions of CO2 into the ocean and atmosphere, according to 32 of the world’s leading marine scientists.

That key conclusion highlights a series of warnings and recommendations developed by the new International Working Group on Coastal “Blue” Carbon, which first met in Paris last month.

Restored mangroves around a shrimp farm
Restored mangroves around a shrimp farm in Batangas, Verde Island Passage, Philippines. Mangroves provide coastal protection from storms, reduce the impacts of floods and are important fish nurseries, but they are being damaged by human activities and are becoming increasingly susceptible to climate change related impacts. Photo © Conservation International/ Giuseppe Di Carlo

Much of the carbon emitted when mangroves, seagrasses or tidal marshes are destroyed is estimated to be thousands of years old because the CO2 stored in these ecosystems is found not only in the plants, but in layer upon layer of soil underneath. Total carbon deposits per square kilometre in these coastal systems may be up to five times the carbon stored in tropical forests. This is due to their ability to absorb, or sequester, carbon at rates up to 50 times those of the same area of tropical forest. The management of coastal ecosystems can supplement efforts to reduce emissions from tropical forest degradation, the experts say.

According to the scientists from 11 countries on five different continents, the existing knowledge of carbon stocks and emissions from degraded or converted coastal ecosystems is “sufficient to warrant enhanced management actions now.”

Disappearing mangroves

Dr. Emily Pidgeon, Marine Climate Change Director at Conservation International, said “We have known for some time the importance of coastal ecosystems for fisheries and for coastal protection from storms and tsunamis. We are now learning that, if destroyed or degraded, these coastal ecosystems become major emitters of CO2 for years after the plants are removed. In the simplest terms, it’s like a long slow bleed that is difficult to clot. So we need to urgently halt the loss of these high carbon ecosystems, to slow the progression of climate change.”  

Scientist studying seagrass, Madagascar
Scuba-diving scientist studying seagrass, Madagascar. Photo © Keith A. Ellenbogen/iLCP

Draining a typical coastal wetland, such as a mangrove or marsh, releases 0.25 million tons of carbon dioxide per square kilometre for every metre of soil that’s lost. Global data shows that seagrasses, tidal marshes, and mangroves are being degraded or destroyed along the world’s coastlines at a rapid pace. Between 1980 and 2005, 35,000 square kilometres of mangroves were removed globally – an area the size of the nation of Belgium. This degraded area still continues to release up to 0.175 gigatons of carbon dioxide each year – equivalent to the annual emissions of countries such as the Netherlands or Venezuela.

Wendy Watson-Wright, Exective-Secretry of the Intergovernmental Oceanographic Commission added, “Scientific studies have shown that although mangroves, seagrasses and salt marshes account for less than 1 percent of the total plant biomass on land and forests, they cycle almost the same amount of carbon as the remaining 99 percent. So the decline of these carbon-efficient ecosystems is a valid cause of concern.”

 To view the Intergovernmental Oceanographic Commission's full recommendations, visit