Coastal mangroves store more than 6.4 billion tons of blue carbon around the world, with more than 90% of it held in the soil, according to new research produced by the Woods Hole Research Center and released last month by the Global Mangrove Alliance.

The total carbon sequestered is about 4.5 times as much as the U.S. economy emits in a single year. Based on remote sensing data at a resolution of 30 metres, Woods Hole concludes that mangrove forest destruction released 30 to 122 million tons of carbon between 2000 and 2015.

“Halting the loss of further mangrove habitat and restoration of lost habitat will not solve climate change alone,” said lead author Dr. Jonathan Sanderman. “But for many nations, including most small island nations, mangrove protection and restoration represent one of the most viable climate mitigation options.”

The research centre notes that direct measurement of soil carbon storage has only been carried out in about one-third of the 100 countries around the world that contain mangroves. “To fill this measurement void, the researchers developed a machine learning-based model to predict soil carbon storage based upon climatic, vegetation, topographic, and hydrologic properties that can be inferred from satellite data. Using this model, they could then estimate the carbon storage within any mangrove forest in the world.”

The research team came up with its calculation of soil carbon loss by overlaying remotely-sensed deforestation data onto its baseline map of soil carbon.

“Effective action on climate change will require a combination of emissions reductions and atmospheric carbon removals,” Sanderman noted, which means that “protecting, enhancing, and restoring natural carbon sinks must become political priorities.” He added that “mangrove forests can play an important role in carbon removals because they are among the most carbon-dense ecosystems in the world, and if kept undisturbed, mangrove forest soils act as long-term carbon sinks.”