Capturing carbon in the coastlands

One of the main reasons why we are yet to experience the full weight of climate change is that the oceans absorb a lot of the CO2 emissions from human activity. CO2 is absorbed into seawater, and it is also sequestered in plant plankton. This is really useful, but unfortunately neither of these functions can be accelerated or encouraged to help mitigate climate change.

It would be great if we could stash away more of our emissions by dissolving them in seawater, but that’s the driver of ocean acidification, which is a problem in itself.

And while it is possible to encourage the bloom of phytoplankton, that’s how marine dead zones are created. It has been suggested that seeding the oceans with iron would stimulate algae growth, but it could kill off all other marine life in the process.

So really both of those are off the table, but there is one other option that’s received less attention. If we focus on the coast, on swamps and salt marshes, there are ecosystems that can lock away carbon effectively and safely. The key is that the carbon is sequestered through soil instead of seawater. When it dies, plant life in coastal wetlands sinks to the bottom and is trapped by roots, rather than washing away in the tides. There it settles into peat, accumulating over centuries into layers and layers of mud, sometimes as deep as 10 metres thick. It is stable, and can remain undisturbed for centuries.

This makes coastal wetlands one of the most productive carbon stores on the planet, and why we should do what we can to protect mangrove swamps, salt marshes and seagrass meadows. We can also create new ones where we can. Since they are great for biodiversity and can help to control flooding and serve as natural sea defences, it’s a good idea from all sorts of angles.

Here’s a little graphic from the Nature Conservancy’s Mapping Ocean Wealth project, where you can find out more.