Scientists at Duke University say their analysis is the most comprehensive estimate of global carbon emissions from the loss of these coastal habitats to date and shows the importance of keeping these coastal-marine ecosystems intact.
Carbon captured through biological processes and stored in the sediment below mangroves, sea grasses and salt marshes is called "blue carbon," researchers said.
When these wetlands are drained and destroyed, the sediment layers can release large amounts of carbon dioxide, they said.
"On the high end of our estimates, emissions are almost as much as the carbon dioxide emissions produced by the world's fifth-largest emitter, Japan," researcher Brian Murray said in a Duke release Thursday.
"This means we have previously ignored a source of greenhouse gas emissions that could rival the emissions of many developed nations."
The critical role of these ecosystems for carbon sequestration has been overlooked, researchers said.
"These coastal ecosystems are a tiny ribbon of land, only 6 percent of the land area covered by tropical forest, but the emissions from their destruction are nearly one-fifth of those attributed to deforestation worldwide," co-author Linwood Pendleton said.
"One hectare, or roughly two acres of coastal marsh, can contain the same amount of carbon as 488 cars produce in a year.
"Comparatively, destroying a hectare of mangroves could produce as much greenhouse gas emissions as cutting down three to five hectares of tropical forest."