Salt marshes will suck CO2 from air faster and faster as seas rise

Runaway global warming gets more negative feedback

Salt marshes and similar types of coastal terrain could act naturally to fight global warming by absorbing increasing amounts of carbon in a warming world, scientists have found. Even better, salt marshes' carbon-sequestering effects would actually be increased sea-level rise.

Salt marshes, mainly made up of specialised grasses and their root systems, are a common type of coastal environment. They trap silt, serving to build up the elevation of the coastline and so resist storms and flooding. As the seas rise, the marsh rises too, as professor Matt Kirwan (Virginia uni) explains:

“One of the cool things about salt marshes is that they are perhaps the best example of an ecosystem that actually depends on carbon accumulation to survive climate change: The accumulation of roots in the soil builds their elevation, keeping the plants above the water,” says the prof.

According to a statement announcing Kirwan and his colleagues' new research into salt-marsh carbon effects:

Salt marshes store enormous quantities of carbon, essential to plant productivity, by, in essence, breathing in the atmospheric carbon and then using it to grow, flourish and increase the height of the soil. Even as the grasses die, the carbon remains trapped in the sediment. The researchers’ model predicts that under faster sea-level rise rates, salt marshes could bury up to four times as much carbon as they do now.

“Our work indicates that the value of these ecosystems in capturing atmospheric carbon might become much more important in the future, as the climate warms,” adds Kirwan, noting that other types of saltwater coastal terrain such as seagrasses, mangrove swamps etc would be likely to show similar effects.

All in all the salty swamps and marshes of the world seem set to provide a noticeable negative feedback process as and when global warming gets underway for real, one which will need incorporating into climate models.

The good prof notes however that marshes can't cope with sudden, massive rises in sea levels, only gradual ones. So ix-nay on that tidal-barrage project, or you might make global warming worse rather than better.

Kirwan and his colleagues' work is published in hefty boffinry mag Nature - often the sign of a bigtime shift in the scientific world. ®