A recent study from UCSB researchers examined the potential impacts of seaweed aquaculture on carbon offsetting. / Courtesy of Wikimedia Commons

The Intergovernmental Panel on Climate Change (IPCC) has cautioned the world that it is crucial to limit global warming to 1.5ºC and not reach 2ºC above pre-industrial levels to prevent greater “robust global differences in temperature means and extremes.” This requires rapid and intense global reductions in both carbon dioxide and non-carbon dioxide climate pollutants.

Many governments have addressed climate change, and reports and policies such as the Fourth National Climate Assessment, California Climate Action Plan and Paris Climate Agreement stress the urgency to react to climate change. It is perhaps a silver lining that when it comes to environmental markets, carbon markets are now the most expensive markets in the world.

New research by UC Santa Barbara researchers Halley Froehlich, Jamie Afflerbach, Melanie Frazier and Benjamin Halpern, titled “Blue Growth Potential to Mitigate Climate Change through Seaweed Offsetting” and published in Current Biology addresses the impact that seaweed farming could have on carbon offsetting, as well as other ecological benefits. Carbon offsetting is compensating for emissions of another industry or human activity with a process that reduces carbon emissions to a net zero.

Seaweed naturally plays a role in the sequestering of carbon by storing carbon in their tissues that is then exported to the deeper ocean via what the study calls a “biological pump.” The carbon is deposited on the seafloor, in the depths of the ocean and out of the atmosphere.

Currently seaweed is farmed, but on a scale that would only account for 1% of carbon sequestration if it were deposited in the deep ocean.

Seaweed is currently grown for use in food, medicine, biotechnology and cosmetics. At the current scale of farming it is a carbon negative operation, meaning that it could also offset many other forms of popular aquaculture.

“We found seaweed aquaculture could offset all of finfish and aquaculture (even with accounting for seaweed farming emissions) with sinking just 14-25% of current standing farmed production in the deep ocean,” Frazier explained in an email.

It is a viable solution on a regional scale, especially in areas with favorable climates such as California, but lacks the ability to make an impact on a global scale. To be able to acquit the world of its carbon emissions produced by agriculture — around 5.1 billion tons per year — seaweed farming would have to increase from the current 1.9 thousand km² to 7.3 million km², which represents 15% of the ocean that is potentially habitable for seaweed aquaculture, according to the study.

“We found it is unlikely seaweed aquaculture alone could scale to address global agricultural emissions,” Frazier detailed.

That’s not to say that efforts such as this done globally would not add up. The study goes as far as to assert that it could be beneficial to progressive countries or ones with bold economies tailored to circumvent carbon emission whilst supporting Blue Growth Initiatives, which is the Food and Agriculture Organization of the United Nations’ (FAO) framework for sustainably developing fisheries and aquaculture.

A look at the economic viability of seaweed farming indicates some obstacles. One being that if farmed seaweed was harvested solely for human use it would greatly reduce its potential to offset carbon emissions. A portion of the seaweed grown would need to be deposited out at sea, but what economic incentives would there be to persuade farmers to do this extra work and lose a portion of their income?

According to Frazier, “That is a huge hurdle, which we highlight in the paper. Policy changes and integration into the voluntary carbon market are key, alongside reduction in farming costs. Economies of scale would help, but it is not a simple ask.”

The implementation of effective policy remains complicated, and while this is the case, aquaculture growth remains speculative.

Halpern addresses over email, “In California, policy (rules and regulations) make rapid growth of aquaculture unlikely, so there is not likely a fast way to do this.”

Different marine environments were canvassed via data sets to locate areas where seaweed aquaculture showed the most benefits and viability. California proved to have an ideal climate for seaweed aquaculture as well as thriving populations of the giant kelp Macrocystis pyrifera.

Seaweed aquaculture appears to be a clever choice for carbon offsetting, but its benefits do not end there.

As Frazier puts it, “Seaweed aquaculture also has ‘charismatic carbon’ potential. That is, it can serve multiple purposes, not just carbon capture, including local buffering of acidic ocean conditions and improving water quality.”

Even if the goals of carbon offsetting are not fully realized, seaweed farming has also showed promising signs for carbon offsetting as well as other environmental benefits such as restoring eutrophic, hypoxic or acidic waters to their natural equilibrium.

Halpern details the process, “Seaweed pulls nitrogen from the water to grow (like being fertilized, but nitrogen is naturally in the water). Eutrophication is excess nitrogen in the water, so seaweed draws that excess nitrogen out of the water.”

Hopefully in years to come, aquaculture will emerge as a viable industry with many ecological benefits.