Seaweed: climate superhero?

Some of my most vivid childhood memories stem from being on Cornish beaches, playing with this stuff. Seaweed.

It's hard not to love its unique smell and - with some varieties - popping its bubble-wrap-like air pockets.

Increasingly, though, seaweed is also being seen as a potential solution to the climate crisis. How exactly, though? In three ways.

Ocean afforestation
Seaweed grows much quicker than land-based plants, even those grown with manufactured fertilisers. It can therefore absorb CO2 more quickly. Seaweed doesn't need to expend energy on growing structures to counteract gravity (e.g. a trunk or thick stem) or deep roots for gathering moisture. For this reason, some oceanic species like kelp can grow up to a metre a day.

A charity called The Climate Foundation, has designed a patent pending structure for growing kelp on vast scales, at depths of 25m. It includes a wave-driven pump to draw up cooler, nutrient rich water from beneath the 'thermocline layer',  accelerating the kelp's growth. Once fully grown, this kelp, which has absorbed CO2 during its rapid growth, would be cut and dropped to the seabed far below, sequestering the carbon. The charity have permission to test this in waters off The Philippines, where thousands of farmer co-ops already grow seaweed. The variety of seaweed being grown alters the acidity of the surrounding sea, to the point where shellfish will grow at an enhanced rate, so they would be farmed inside the structures.

If you want to know more about this program, see the foundation's description, or watch the TED talk that describes the logic.

Reducing cattle methane
Humans keep a lot of cows, and they (the cows!) burp methane produced in their digestive tracts. Terrible for the environment, obviously. Cutting beef from your diet would be a great step towards a more sustainable future, but even if a large proportion of us did this there would still be cows. In India they are considered holy, for instance.

Anything that could reduce the methane production of cows would be a plus, then. Researchers and  farmers in Australia and Canada, respectively, have discovered that adding certain seaweeds to the bovine diet can neutralise a substantial proportion of the methane which they produce. We should bear in mind, however, that cattle raising has a broader negative environmental impact, and that lower-impact feeds could be considered a 'get out of jail free' card for continued unsustainable cattle farming.

Energy production

Seaweed, technically macroalgae, can also be turned into biofuels such as bioethanol, by breaking down and extracting their lipids structure. Some argue that its microscopic cousin - microalgae - is better placed for this. NASA, in particular, has been researching the cultivation of microalgae using seawater, for the production of liquid fuels.

Seaweeds can also be utilised in the production of biogas, which can be used to drive onsite gas engines or turbines, to produce distributed power, or upgraded into biomethane for injection into the gas grid. Either way, seaweed doesn't compete with space for food crops, which often - and contraversially - make up substantial proportions of biogas plant feedstock. If farmed and transported without using too many fossil fuels, the resultant gas or electricity could be very low carbon. Or even, conceivably, negative.

This use of seaweed in biogas production has also has been researched in depth, and the conclusions are that you need to bring the moisture levels down to just to right level, use certain varieties in the right combination with other feedstocks, and maintain a constant supply throughout the year.

These challenges are remediable, and for Anaerobic Digestion plants near to the coast, appropriately dried stocks of seaweed might  be a good supplement. Many AD plants in the UK struggle to make ends meet, as there is great competition for feedstock - particularly food waste - and the 'gate fee' income that they have traditionally depended upon has collapsed. The knack is to bring production costs down, by scaling it up.

If you want to know more, see the results of the British-funded research projects Biomara and SeaGas.

So next time you are on the seashore, and you spot some seaweed, take a moment to consider just how useful this overlooked family of plants could be for our future.