Black Carbon, Brown Carbon… What About Blue Carbon?

By: TANJA SREBOTNJAK, Director of the Hixon Center

While working on a small consulting project, I recently came across the term “blue carbon.” I’m familiar with black carbon (i.e., the soot emitted during incomplete combustion of fossil fuels in coal-fired power plants, cars and other equipment), and brown carbon (which originates primarily during the combustion of organic biomass and is a close cousin of black carbon). Black and brown forms of carbon are both very important for climate change, since their respective light and heat absorptive properties impact the greenhouse balance of the planet. They also adversely impact human health due to their contribution to smog. As a general rule, we want to limit black and brown carbon.

But what is blue carbon? I hadn’t heard the term before and it almost sounded like it could be a good type of carbon. So, I looked it up: blue carbon is the carbon captured by the oceans and coastal ecosystems. Coastal vegetated landscapes, such as mangrove forests, salt marshes, and sea grass beds, are highly productive at sequestering carbon, storing it in above- and below-surface biomass such as stems, leaves, root material and sediments. Although these habitats cover less than 0.5% of the oceans’ seabed and shore areas, they are responsible for 50%-70% of all carbon absorbed by ocean sediments. Not only do ocean and coastal ecosystems store a lot of carbon, but they also do it quickly. Salt marshes, for example, have a carbon sequestration rate that is over 50 times faster than tropical rainforests. Blue carbon potential is thus a relevant means for controlling atmospheric greenhouse gas concentrations.

Unfortunately, blue carbon sinks are at risk worldwide as a result of expanding coastal human settlements, removal for a growing global aquaculture industry, and general ecosystem decline due to pollution and climate change. Indeed, the rate of loss of these important blue carbon sinks is higher than those of any other ecosystem, including rainforests. At current loss rates of 2-7% per year, it will take little more than another generation for the world’s last mangrove forests to disappear.

It is highly important to protect blue carbon sinks – not just for their climate benefits, but also because they provide valuable habitat for marine and coastal flora and fauna and hence the livelihoods of thousands of fishing communities. They also mitigate storm surges, thereby serving as a natural, first line of defense against hurricanes and tsunamis. Mangrove and wetland restoration is, furthermore, advocated as a low-cost means to create buffer zones for sea level rise that are far more effective, longer-lasting and economically valuable than concrete sea walls.

So, with all that said, know your carbon – and treat it accordingly!