Blue Planet 2: Green Seas (and Blue Carbon)

The capacity of coastal habitats to capture and store carbon is a huge research interest of mine, so when David Attenborough talked about it on Blue Planet 2 earlier this evening I couldn’t have been more pleased!

Tonight’s episode was called ‘Green Seas’, and covered habitats and ecosystems often passed over by documentary makers in favour of more ‘charismatic’ ocean dwellers: seagrass meadows, kelp beds, mangrove forests and algal blooms.

What each of these have in common is that, well, they are green plants.

Green plants photosynthesise, using the pigments which give them their colour to transform light energy into sugars. To do this, they take in carbon dioxide (CO2) from the atmosphere, strip off the carbon atoms, and produce oxygen (O2).

Huge efforts are being made across the globe to reduce the amount of CO2 we are adding to the atmosphere in an effort to slow climate change down. Just telling people to reduce the amount of CO2 they release hasn’t worked, and so we have begun to look for ways to mitigate or ‘cancel out’ some of those emissions too.

Ideas about how we might do this are wide ranging and generally fall into the category of ‘geoengineering’ options, where we use a combination of technology and our understanding of natural systems to manipulate them. Studies have been commissioned to look at whether fertilising the oceans with iron might stimulate increased CO2 uptake by phytoplankton and algae. Carbon Capture and Storage (CCS) plants are now operational and capture CO2 produced by power plants before it enters the atmosphere so it can be condensed then pumped into empty oil wells where it will be stored for tens of thousands of years. Scientists are even looking at the possibility of forming deep-sea lakes whereby CO2 is pumped deep into the ocean and pressure stops it from rising back up again. None of these options is without issue.

I work in a related area of marine science called ‘blue carbon’, which started as a term to distinguish carbon produced and stored in the ocean (blue) from carbon produced and stored on land (green) but has since come to represents a sub-discipline of scientists who look at ways to protect, support and maximise the carbon storage capacity of ocean ecosystems in order to slow the rate of climate change.

To do this, we tend to focus on 3 main habitats (seagrass beds, intertidal saltmarshes and mangrove forests) which we call coastal wetlands. These wetlands cover less than 2% of the ocean by area, but are responsible for around half of the total CO2 taken up by the marine environment (which is 70% of the global total).

You see, although ocean plants take in carbon dioxide much the same way as land plants do, they tend to do it much more effectively, and for much longer. Indeed, an acre of seagrass bed can be around 10 times as effective as an acre of pristine Amazon rainforest when it comes to taking up and storing carbon, and can store carbon for hundreds to thousands of years. Millions, even, if that carbon makes it into the rock cycle.

But whilst the rainforest has international protection measures in place to help protect it, seagrass beds do not and are being lost 4 times as fast. Over half of the world’s coastal wetlands have been lost since the 1960s, and today’s rate of removal (340,000 – 980,000 hectares per year) is equivalent to 20-30% of our total annual carbon emissions.

The destruction of these habitats is generally financially motivated, with destructive fishing practices and coastal pollution being the major culprits. Efforts to educate stakeholders and change behaviour patterns have proven relatively unsuccessful, and so we have to try something else. Land-based schemes which put a financial value on forests based upon their ability to store carbon have proven an effective means of habitat conservation in instances where the costs involved in deforestation make it the least profitable option. Perhaps a similar scheme might work for ocean ecosystems?

The thing is, the world’s coastal zones are incredibly dynamic, diverse places which can be much more sensitive to change than their terrestrial counterparts. They are also mostly underwater, which makes them a lot harder to incorporate into trading frameworks than their terrestrial counterparts. For an example, saltmarshes which have been storing carbon for thousands of years can release their entire stash back into the atmosphere in a matter of months if their access to salt water is restricted. And no one wants to invest in something that won’t be there for very long.

That’s where scientists working on blue carbon come in: we are the ones who need to develop new methods to measure carbon storage and to understand how these systems might change over time. It’s not an easy job, but if the Blue Carbon Economy becomes a reality, we’ll have found a way to help ease climate change whilst protecting vulnerable coastal habitats

The Blue Carbon Initiative is an amazing resource for finding out more about Blue Carbon.