We Need to Harness Natural Carbon Sinks to Reverse Climate Change
By: Danny Schleien
Tags: Carbon, Climate Change, Science, Environment, Emissions

The Oceans:

We often forget how much of the Earth is covered in water. Many people go their entire lives without seeing the ocean or feeling its presence. And some see it as a mysterious and scary expanse.

Oceans cover about 70% of the Earth’s surface. They are in many ways the lifeblood of the planet.

They’ve also mitigated quite a lot of the bathtub filling we’ve done over the last couple of centuries.

And if we want to empty the bathtub, we’d be wise to think blue.

The holy trinity of oceanic natural carbon sinks — seagrass, mangroves, and marshes — falls within the umbrella of blue carbon, arguably the most underappreciated ally nature has provided us in the fight against climate change.

Blue carbon refers to the carbon captured by oceanic and coastal ecosystems. Coastal habitats in particular cover less than 2% of the total ocean area but account for approximately half of the carbon stored in ocean sediments. They are literally the blue-chip of oceanic carbon sinks.

Trapped underwater, seagrass can store carbon for hundreds of years in an anoxic environment, decomposing more slowly than terrestrial plants. Despite occupying only 0.2% of the ocean floor, seagrass accounts for 10% of oceanic carbon capacity.

At a rate of 1.5% annual habitat loss, seagrass is disappearing faster than tropical rainforests. But seagrasses store much more carbon — 83,000 tons per square kilometer vs 30,000 tons per square kilometer.

Seagrass might not even be the best carbon sink compared to other coastal ecosystems. One study claims mangroves and salt marshes are both about 50% more effective at burying carbon.

But mangroves are highly susceptible to destruction from both rising sea levels (driven by global heating) and habitat destruction for anthropogenic purposes (often aquaculture and other forms of coastal development). Warmer water adversely affects ocean salinity, reducing the carbon sequestration capacity of mangroves.

Given the prodigious benefits mangrove forests provide — from flood alleviation to storm surge mitigation to pollutant filtration to wildlife protection — beyond their carbon sequestration, protection of mangrove habitat should be of paramount concern to global climate policymakers.

Mangroves sequester about four to five times as much carbon as tropical rainforests, but we only have about 140,000 square kilometers of mangrove forest left.

Salt marshes are similarly effective at storing carbon as mangroves, burying organic material about 55 times faster than tropical rainforests. Salt marshes are prone to nitrate pollution from anthropogenic sources, which diminishes their carbon sequestration capacity. As with mangroves, marshes stand to disappear without meaningful conservation efforts and more importantly, decarbonization.

Collectively, we’ve destroyed a large proportion of the world’s blue carbon. “Globally, we’ve lost up to half the world’s mangroves since the 1940s. A quarter of the world’s tidal marshes have been lost since the 1800s. And the world has lost half its seagrasses just since 1990.”

The onslaught on blue carbon and associated coastal ecosystems represent both a glaring mishap in conservation practices and a glaring opportunity to increase nature’s ability and capacity to store carbon.

According to Project Drawdown, protecting coastal wetlands (which include seagrass, mangroves, and salt marshes) would secure an estimated 15 gigatons of carbon, equivalent to about 1.5 years of global carbon dioxide emissions (and roughly 2 ppm of atmospheric carbon dioxide concentration, since 1 ppm is equivalent to 7.76 gigatons of CO2).

Beyond storing carbon, coastal ecosystems provide storm and flood protection and protect biodiversity among other essential ecological benefits. For example, coastal wetlands prevented more than $625 million of potential damage from Hurricane Sandy across the Northeast.

We should leave the oceans to their own devices and help us empty the atmospheric bathtub. But the oceans have already shouldered a huge burden, and there’s a better natural carbon sink right below our feet.

Yes, I’m talking about the soil.