Tidal marshes are powerful allies in the fight against climate change due to their remarkable ability to store carbon. Until now, our understanding of how much carbon these marshes store globally was limited, with estimates based mostly on studies from a few regions.
Our recent study created the most comprehensive and detailed global map yet of the carbon stored in tidal marsh soils. Using a machine-learning approach, we analysed soil data from 3,710 marsh locations worldwide, combined with satellite imagery and environmental data, to produce a detailed inventory of tidal marsh carbon storage.
Globally, we found that tidal marshes store approximately 1.44 billion tonnes of carbon in just the top metre of soil, with a significant portion – about one-third – located in marshes across the United States. Our study showed that the amount of carbon stored in these ecosystems varies widely by region, driven by differences in climate, geography, and tidal patterns.
We discovered that tidal marshes store substantial amounts of carbon, averaging 268 tonnes per hectare in the top metre of soil. Marshes in temperate regions, particularly the northern Atlantic and Pacific areas, emerged as major carbon reservoirs. Interestingly, we found that marshes in colder climates often store more carbon per hectare compared to their tropical counterparts, challenging some previous assumptions.
Despite their critical role, tidal marshes have experienced significant losses globally due to climate change, sea-level rise, and human activities like urban expansion and agriculture. More than half of the world’s tidal marshes have been lost since 1800, underscoring the urgent need for conservation and restoration efforts.
Our study highlights several areas of uncertainty, notably in the Arctic and tropical regions, where data remains sparse. This points to the urgent need for more targeted research and data collection in these regions to better inform global climate strategies.
This comprehensive global inventory provides a crucial baseline for including tidal marshes in national and international climate policies. By accurately mapping their carbon stocks, countries can now better account for these ecosystems in their climate strategies, potentially unlocking new funding and support for marsh conservation and restoration.
In short, our global tidal marsh map underscores these coastal habitats’ immense value and the necessity of protecting them to harness their full potential in mitigating climate change.