In the fight against climate change, humanity owes the ocean a big thank you. It has already absorbed nearly one-third of the carbon emissions from human activities such as the burning of fossil fuels.
But many researchers think the ocean can shoulder even more of the burden, with technologies that would enhance its natural ability to suck carbon from the air and store it for centuries. But to better understand how such strategies might change the ocean—or whether they would even work—funders will need to pour as much as $2.5 billion into research over the next decade, a U.S. panel of leading ocean scientists recommended today.
The funding would dwarf current spending in a field where interest is high but key questions remain unanswered, says Scott Doney, a University of Virginia oceanographer who chaired the National Academies of Sciences, Engineering, and Medicine (NASEM) committee. Its report was sponsored by the ClimateWorks Foundation, a nonprofit that funds research on climate solutions, and the authors hope it will influence U.S. funding agencies, as well as entrepreneurs, corporations, and charitable groups.
Even if nations make steep cuts to greenhouse gas emissions, many scientists believe the world will need to pursue “negative emissions technologies” that would pull carbon dioxide (CO2) and other warming gases from the air in order to prevent more severe climate change. Although billions of dollars have gone into land-based schemes that, for instance, promote reforestation or agricultural practices that store more carbon in the soil, less attention has been paid to ocean technologies, Doney says. “The ocean is a relatively new space” when it comes to carbon sequestration research, he says.
The panel considered six ways the ocean might be coaxed to take up still more carbon: rehabilitating coastal ecosystems; growing seaweed such as kelp; spurring plankton production, either by forcing nutrients up from deep in the ocean or by dumping them into the water; stripping CO2 from seawater; or making parts of the ocean more alkaline so it can absorb more CO2.
Some of the more natural approaches, like replanting coastal mangrove forests, are seen as relatively benign—the ocean equivalent of reforestation. But the panel also considered industrial-scale interventions that could alter ocean chemistry, such as using ground up iron to trigger massive plankton blooms or converting thousands of square kilometers of open ocean into seaweed farms. Those approaches verge on “geoengineering,” a dirty word for many ecologists concerned about the consequences of tampering with Earth systems.
Much of the research remains in its infancy, confined to computer models, lab experiments, or small-scale field tests, Doney says. Even one of the most heavily tested and controversial methods—fertilizing plankton blooms—faces questions about its effectiveness and potential for affecting ocean ecosystems.
In the 1990s, scientists began a series of around a dozen iron fertilization experiments, which led to blooms of phytoplankton that, like trees, draw down CO2. But it’s not clear whether much of that carbon actually remained sequestered when the phytoplankton died and sank toward the ocean floor, says Stephanie Henson, a marine biogeochemist at the United Kingdom’s National Oceanography Centre. A recent survey of 13 past experiments found that only one reduced carbon levels deep in the ocean, where carbon is likely to stay put for decades or longer. “I think ocean fertilization quite possibly is a nonstarter,” Henson says.
Others, however, are undeterred. David King, a chemist and head of the Centre for Climate Repair at the University of Cambridge, is preparing an experiment next summer in the Arabian Sea in collaboration with scientists at India’s Institute of Maritime Studies in Goa. There, they plan to test whether floating rice husks can deliver iron nutrients to fuel plankton growth more efficiently. “There’s an enormous amount of naysaying going on,” King says. “There are many, many people saying let’s leave the oceans alone, as if we haven’t already interfered with them.”
He envisions a time when iron fertilization of 2% to 3% of the ocean each year would trigger a biological cascade in which massive plankton blooms would feed fish larvae that would, in turn, support larger whale populations, which would then fertilize the plankton growth with their feces. Unpublished calculations suggest the process “would remove an enormous amount of greenhouse gases from the atmosphere,” King says.
The NASEM committee recommends spending $250 million on ocean fertilization tests larger than 1000 square kilometers, partly to better understand what happens to the carbon and surrounding ecosystems. Iron supplementation and seaweed cultivation “offer the greatest opportunities” for experiments to better understand biological approaches to sequestering carbon in the ocean, the panel says.
Other ocean scientists are working on a smaller scale. Jess Adkins, a geochemist and oceanographer at the California Institute of Technology, is about to start building a prototype to strip CO2 from the exhaust of ocean freighters by funneling it through a mixture of limestone and saltwater, triggering a chemical reaction that would create dissolved bicarbonate, which remains sequestered in the ocean. “This is the antacid for the ocean,” Adkins says. “This is like literally taking Tums.”
He hopes a similar device could eventually be built into new ships, helping the maritime industry reduce its nearly 3% share of global carbon pollution. Such a targeted approach, he says, might stand a better chance of success than ideas to spread bits of limestone, olivine, or other carbon-absorbing alkaline minerals across vast swaths of the ocean, or to pump alkaline water into the sea from coastal factories. The energy needed to fuel such operations could outweigh any carbon gains in the ocean, he says. Still, the NASEM committee gave top billing to studying whether processes to make the ocean more alkaline might pay off. Such approaches have “considerable” potential, although potential environmental impacts haven’t been quantified, the panel found.
If any of these approaches prove viable, Doney cautions against overestimating the effect they could have on the climate problem. Even if fossil fuel emissions are cut substantially, humans will need to remove an estimated 10 to 20 gigatons of carbon pollution from the atmosphere each year to meet targets aimed at keeping global temperature increases below 2°C by 2100. Making a dent even in that part of the carbon budget requires action on a vast scale, Doney says. “There’s no single solution,” he says. “It’s going to have to be lots of things that are relatively substantial.”