WASHINGTON—As global leaders struggle to cut greenhouse gas emissions, a cost-effective way to reduce the amount of carbon dioxide (CO2) released into the atmosphere may lie in preventing the loss of mangrove forests found on the coastlines of most tropical nations, according to a study released today by a team of researchers from Resources for the Future (RFF) and the University of California, Davis.
Mangroves, which are among the most unique and rapidly disappearing natural environments in the world, store enormous amounts of carbon in the earth below their roots. When these coastal habitats are disturbed by changes in land use, the so-called "blue carbon" locked away in the bodies of the plants or in the soil is gradually exposed to air and released as CO2 into the atmosphere.
Co-authors Juha Siikamäki, James Sanchirico, and Sunny Jardine estimate that protecting mangrove forests from development can reduce CO2 emissions at a cost of less than $10 per ton of CO2. Given current market prices for carbon offsets, this suggests that mangroves are worth saving for their carbon storage potential alone. The team's findings appear today in the Proceedings of the National Academy of Sciences.
The researchers developed first-ever global and high-resolution spatial estimates (at a 9 km by 9 km level) of projected emissions from mangrove loss to create a set of global supply curves for avoided emissions.
"We find that protecting mangroves can be highly competitive with other approaches for reducing global greenhouse gas emissions," said Siikamäki, a fellow at Resources for the Future. "The bonus is that in doing so, we can preserve important habitats critical to coastal fisheries, rich in biodiversity, and home to hundreds of species of plants and animals, many of them endangered."
A conservation strategy based solely on carbon would not automatically target areas most valuable for biodiversity. The team finds, however, that a biodiversity-focused strategy would only modestly raise the costs of a blue carbon program.
"Despite the promise, there are obstacles to taking advantage of blue carbon's potential for reducing global greenhouse gas emissions," said Sanchirico. "Carbon stored in mangroves and other coastal ecosystems (such as seagrasses) isn't yet recognized in international frameworks for carbon offsets. Even if it is, there is a host of monitoring and institutional challenges that require attention."
One serious challenge to realizing the potential for blue carbon may lie in limits to governance capacity. It is plausible that governments with problematic management and institutional environments will be unable to join the carbon market. The researchers find that removing countries that score in the bottom half of the World Bank's index on governance effectiveness reduces the potential blue carbon offset supply by three quarters.
Some Facts on Mangroves and Blue Carbon
- Mangroves account for just 0.7 percent of global tropical forests (around 140,000 km2).
- They possibly store carbon equal to roughly 2.5 times annual global CO2 emissions.
- Between 1990 and 2005, mangrove loss occurred at a rate of about 0.7 percent per year
- Siikamäki, Sanchirico, and Jardine estimate that the cost of protecting mangroves ranges between $4 and $10 per ton of CO2.
- Carbon offset prices in the EU’s Emissions Trading System recently have ranged between $10 and $20 per ton of CO2.