Planting trees is not the only way to offset carbon for climate mitigation. Farming seaweed in our oceans could be another promising tool for the carbon neutrality toolbox, according to a new study.
A first-ever global assessment of seaweed aquaculture’s carbon offsetting potential, the study shows that coastal countries around the world, including the United States, could benefit from adding seaweed farming to their carbon offset markets.
“It’s not a silver bullet, nor an industry that exists yet. But it has huge potential,” said lead author Halley Froehlich, an assistant professor in UCSB’s Department of Environmental Studies and in the Department of Ecology, Evolution and Marine Biology.
The study was published in the journal Current Biology and conducted by a team from the National Center for Ecological Analysis and Synthesis (NCEAS) at UC Santa Barbara, where Froehlich was a postdoctoral researcher when they conducted the analysis.
Froehlich and co-authors Jamie Afflerbach, Melanie Frazier and Benjamin Halpern from NCEAS synthesized diverse datasets from scientific literature to understand seaweed aquaculture’s carbon sequestration potential. The process would involve cultivating seaweed and harvesting it for the purpose of sinking the algae in the deeper ocean, where the carbon stored in its tissues would remain ‘buried.’
“We really wanted to know if it could be beneficial, but also be realistic about its potential,” Froehlich said of the research, which they bounded with constraints including nutrients, temperature and geographic suitability, as well as assessed production growth and cost. The researchers also investigated the mitigation potential on various scales with a focus on the food sector — a major source of greenhouse gases and considerable hurdle to fight climate change.
While farming seaweed alone won’t balance emissions from global food production, due in part to cost and growth constraints, the researchers did find that farming seaweed in a piece of the ocean the size of Palau, or 0.001 percent of the ocean’s ecologically suitable area, could potentially make the global aquaculture industry, one of the fastest growing food sectors, carbon neutral.
Seaweed farming may have the most potential when it comes to achieving local carbon neutrality goals. For example, in the United States, where aquaculture is still a nascent industry, California could offset the carbon produced by the state’s agriculture sector, one of the world’s largest, using only 3.8 percent of the West Coast EEZ area to cultivate seaweed for carbon sequestration.
While no measurable seaweed farming was occurring in the United States in 2016 — the most recent time period of the study — small seaweed farms are starting to emerge in the U.S., though primarily for food and other commercial purposes, not for carbon sequestration.
The U.S., meanwhile, is the world’s second-biggest emitter of greenhouse gases, Froehlich pointed out, underscoring the need for solutions such as seaweed farming to mitigate the millions of tons of carbon dioxide equivalents the country emits per year. Fortunately, seaweed farming has other appealing and beneficial environmental effects, she noted.
“We like to call it ‘charismatic carbon’ because it has additional benefits,” Froehlich said, “such as potentially providing habitat for fish and other marine life, reducing ocean acidification and oxygen depletion, and taking up excess nutrients in local areas.”
The study was a “could we do it?” exploration – proving that yes, we potentially could – and is a start to understanding the full picture of the opportunities and costs associated with farming seaweed to offset carbon. The authors stress that seaweed offsetting is not a silver bullet to global carbon neutrality and recognize carbon offsets are a contentious strategy.
“The problem has become too big for simple solutions. We need all hands on deck,” said co-author Ben Halpern, director of NCEAS.
While solutions to climate change will not be easy, he added, the more strategies, the better.