At a time when the Amazon is burning, there is a growing interest in developing carbon-absorbing forests that warm the planet but resist fire.
This is because these forests are under water.
More and more research is documenting the potential of seaweed cultivation to combat climate change as deforestation decimates rainforests and other key carbon sinks. The fast-growing oceanic jungles of kelp and other macro-algae are very effective at storing carbon. Algae also improve acidification, deoxygenation and other global warming effects on the sea, threatening marine biodiversity and providing food and livelihood for hundreds of millions of people.
"Seaweed finally has its hour of glory," said Halley Froehlich, a marine science scientist at the University of California at Santa Barbara.
She is the principal author of a new study that quantifies for the first time the overall capacity of large-scale seaweed culture to offset terrestrial carbon emissions and map areas of the world. Ocean conducive to the cultivation of macroalgae.
Algae cultivation in only 3.8% of federal waters off the California coast (0.065% of the global ocean conducive to macroalgae growth) could offset emissions from the state's agricultural sector, worth $ 50 billion, according to the newspaper published Thursday in the newspaper. Current biology.
Algae are currently grown on a small scale for use in foods, medicines and cosmetics. Scientists, however, are proposing the creation of industrial-scale farms to grow mature seaweeds, harvest them, and then sink them into the depths of the ocean where captured carbon dioxide would be buried for hundreds or even thousands of years. years.
They discovered that cultivating macroalgae in only 0.001% of the world's seaweed waters and then burying them at sea could offset the carbon emissions of the rapidly growing global aquaculture industry, which supplies half of the world's seafood products. In total, 18.5 million square miles of the ocean are conducive to growing algae, the study concluded.
There is a trap
"Technology does not exist yet" to sequester algae in the depths of the ocean, notes Froehlich. "I hope this paper pushes the conversation between engineers and economists on what it would take for the current mechanisms to be put in place."
Carlos Duarte, a researcher on algae at the Red Sea Research Center in Saudi Arabia, attended a presentation on the findings of the paper in April.
"The new study adds to previous research and global estimates … to make algae aquaculture a major way to mitigate climate change," he wrote in an e-mail noting that he had not examined the final document. "My opinion is that the estimates are very conservative and that the potential is much higher if the crop is maintained properly."
But Duarte opposes the melting of algae.
"Seaweed is a very valuable material and there are better ways to use it while helping to mitigate the effects of climate change than throwing it to the bottom of the ocean," he says.
Indeed, Froelhich and other marine ecologists characterize the carbon of the seaweed "charismatic carbon" in the seaweed for the ability of a Swiss army knife to fight against various environmental ills, in the ocean and on firm ground.
Beyond the potential of algae to combat acidification and deoxygenation, absorb excess nutrients and provide habitat for marine life in at least 77 countries, algae can be turned into biofuel. And research has shown that adding algae to livestock feed can reduce methane emissions from burps of cows and other grazing animals by 70%, a major source of greenhouse gases worldwide. Algae can also be used as a supplement to agricultural soil, replacing petroleum-based fertilizers.
"Calculations show that seaweed can be a very effective tool to fight climate change, but it needs to be validated by the market," says Scotty Schmidt, General Manager of Primary Ocean, a Los Angeles government company. the United States. funded project to develop technologies to deploy large scale algae farms.
"Cultivating algae just for carbon sequestration is not a viable business case at this time because there is hardly a carbon market ready to accept offset credits for algae," she said. he declared.
Primary Ocean's strategy is to extract algae material that can be sold for agricultural purposes. If a profit could be made on these sales and carbon credits were available, the company could then sequester macroalgae waste, says Schmidt.
One of the biggest challenges is to have algae accept algae as a legitimate source of greenhouse gas reduction.
"Science and demand are already there; the bottleneck is a catalyst that allows production to meet demand, "says Duarte. "More specifically, we need carbon credit protocols that can be used to claim carbon credits from marine algae aquaculture, as well as a regulatory environment that facilitates concessions and licenses for aquaculture of marine algae. algae."
Despite a long coastline suitable for growing seaweed, the United States has virtually no offshore aquaculture activity. China and other Asian countries, which produce most of the world's cultivated algae, are expected to play a leading role in establishing macroalgae as a source of 'blue carbon'.
"In the United States, it will probably be easier to get a license for an oil rig than for growing seaweed," says Duarte.