Twining Pushes for CO2 Removal Research in the Boston Globe

The following originally appeared in the Ideas section of the Boston Globe on July 18.

Using the ocean as a carbon sink may be our best hope against climate change

I’ve spent hundreds of days at sea. In the high winds and towering waves of the Southern Ocean around Antarctica, I have worked alongside fellow ocean scientists to understand the impacts of climate change. To stop or slow its effects, humanity must reduce its carbon emissions. However, that is no longer enough: We must also pull carbon dioxide out of the atmosphere and sequester it in the earth or the ocean.

That’s been controversial, but I am researching a way that could have fewer side effects than other proposed methods: ocean iron fertilization — a technique that encourages the growth of microscopic algae, which eat carbon dioxide and then squirrel it away in the ocean’s depths for decades or even centuries.

As someone who has dedicated my life to understanding the ocean, I share others’ concerns about using the ocean to sequester our excess carbon. Intentionally manipulating the marine environment for our own benefit rightly worries many people. However, as the decades have passed, consequences have mounted and alternatives have expired. For Mainers like me, the effects of climate change are hard to ignore. Coastal flooding in January caused an estimated $70 million in damage. The sea level in the Gulf of Maine has already risen nearly a foot in the past century — and is still rising, now faster than ever.

I was a graduate student on the last US-funded ocean iron fertilization project in 2002, and I have spent the past 20 years studying the response of ocean algae to iron in seawater. At the start of my career, carbon dioxide removal was largely on the fringe of the climate change conversation. For many, it was seen as a distraction from emissions reduction efforts. What work was done was funded primarily by entrepreneurs, while most federally funded scientists like me eventually distanced ourselves from early experimentation.

But recent Intergovernmental Panel on Climate Change reports have shown that we can’t achieve climate stability without carbon dioxide removal, and in 2022, the National Academies of Sciences, Engineering, and Medicine issued a report highlighting the need for carbon dioxide removal research. The federal government is already investing billions of dollars in removal projects, with private philanthropy pledging hundreds of millions more.

Just last month, the National Oceanic and Atmospheric Administration and the Department of Energy signed an agreement to pursue marine carbon removal strategies, a promising pathway that relies on amplifying natural processes in the ocean.

The ocean: A natural carbon sink

The ocean covers two-thirds of Earth’s surface, holds 50 times more carbon dioxide than the atmosphere, and holds 15 times more than all land plants and soils combined. About 10 times more atmospheric carbon dioxide moves through the ocean each year than is emitted by human activities. All of this suggests that the ocean might safely store human-emitted carbon without serious harm to its ecosystem.

To that end, several ideas have been put forward to increase the ocean’s capacity to hold carbon dioxide, from expanding seaweed cultivation to deploying electrochemical technologies in order to alter seawater chemistry. All have potential upsides and downsides.

One idea is, essentially, to give the ocean an antacid. Acidification is wreaking havoc in the ocean, so adding minerals that increase the pH of seawater (lowering its level of acidity) both counteracts the effects of ocean acidification and draws down more carbon dioxide from the atmosphere. Scientists are testing the efficacy, costs, and potential side effects of ocean alkalinity enhancement, as that process is known. But the approach isn’t without downsides: It would likely require the mining, transportation, processing, and distribution of billions of tons of rock minerals, significantly increasing mining and transportation activities: The National Academies of Sciences, Engineering, and Medicine estimates that the global shipping fleet and its associated carbon footprints would grow by 10 percent or more. The approach could also result in potentially toxic byproducts like heavy metals making their way into the ocean in the process.

I think ocean iron fertilization may be a better way. Here’s how it would work: Certain nutrients, like iron, encourage the productivity of the microscopic algae that feed on carbon dioxide in seawater. Scientists have considered supercharging that process by fertilizing nutrient-limited regions, like the Southern Ocean around Antarctica, with additional iron to spur large blooms of algae. Those blooms could then draw more carbon dioxide into the ocean, and when the algae die and sink, they would carry that carbon with them to the ocean floor.

In comparison with other options, ocean iron fertilization is low-tech, scalable, and likely to be relatively inexpensive, and unlike building thousands of carbon-capture factories or planting trillions of trees, iron fertilization does not require massive land, freshwater, or energy resources.

But, as with alkalinity enhancement, there are important unknowns. How effective might this approach be? How long would the carbon remain in the deep ocean? What effects would more algae have on oxygen levels and productivity in the ocean? This strategy has been on our radar for decades — yet climate change has far outpaced any research on its effectiveness, costs, and potential side effects.

Early skepticism of carbon removal isn’t the whole picture

The first ocean fertilization experiments were conducted 30 years ago in remote corners of the Pacific and Southern oceans — they showed that more iron stimulates algae growth. However, those early experiments weren’t designed to assess algae’s potential for carbon storage over the long term, and they didn’t explore what the environmental impacts might be of injecting iron into the ocean. In those early experiments, measurements of how much carbon actually sank to the ocean floor were inconsistent, and scientists often couldn’t stick around long enough to monitor the full life of the algae bloom. Nevertheless, a handful of for-profit entities entered the space, some of which proceeded to make unsupported claims that ocean iron fertilization could revitalize fishing stocks or remove large amounts of carbon from the atmosphere.

Like many others in my field, I distanced myself from those early efforts to commercialize ocean iron fertilization, feeling that proponents were overselling the technology and hiding the potential risks — and that we should focus our attention on reducing carbon emissions, not carbon removal and storage.

But the failed promises of those early commercial efforts may not represent the full potential of iron fertilization as a method for carbon removal. I’ve come to believe that we must at least consider large-scale carbon dioxide removal, and I feel an obligation to do what I can to ensure that it is done responsibly and ethically.

Part of that task is helping the public understand the perspective of scientists. I’ve encountered passionate ocean advocates who have shared with me their concerns about the idea of intentionally altering this globally important ecosystem and common resource. Similarly, scientists participating in the early large-scale iron fertilization experiments noted their shock seeing a bloom form in front of their eyes and realizing they’d altered the environment in real time.

But everyone’s daily actions are already affecting the ocean. It has been absorbing our carbon emissions for more than a century. It may seem counterintuitive to ask the ocean to store even more carbon for us, but doing so just might be our best hope.

Better carbon removal methods may be on the horizon

It is time to undertake a new generation of ocean iron fertilization experiments. We need to fertilize larger areas and monitor them for longer. We need to test for possible unintended consequences, like the growth of undesirable toxic algae or the inadvertent production of other greenhouse gases like methane and nitrous oxide. And we need to measure just how effectively — and for how long — carbon is removed from the atmosphere with this method.

Fortunately, we can now supply answers to questions that weren’t possible during early experiments. We have better tools to track the fate of iron and carbon in the ocean, including satellites that monitor algae blooms and advanced buoys that can measure carbon movement when ships can’t be on-site. Our overall understanding of the ocean has also improved.

In my decades of experience working at sea, I’ve been struck by how vast and dynamic the ocean is. Even our largest experimental algae blooms are dwarfed by natural ones. Iron is difficult to dissolve in seawater so it usually takes days of adding it, a little bit at a time, before we see any change. And most of our blooms dissipate in a matter of weeks as they’re rapidly diluted by ocean currents.

That said, more research is needed and should be done by academics and nonprofit organizations to reduce conflicts of interest and improve public accountability. Although private investment and capital will likely be needed to scale any carbon removal technology, that investment first needs to be based on a foundation of rigorous, objective, careful, and transparent research.

There will be tradeoffs involved in carrying out any method of carbon removal on a global scale. Ocean alkalinity enhancement would require major new mining efforts. Ocean iron fertilization could affect the fishing industry and fish stocks in unpredictable ways. We have been unintentionally geoengineering our atmosphere since the Industrial Revolution, and as unpalatable as it may be, we may need to further manipulate the ocean to help fix the problem. The last time atmospheric carbon dioxide was at the current concentration — nearly 3 million years ago — sea level was more than 20 feet above the current level, meaning unless we do something now, we can expect such a rise to happen again.

The climate crisis presents a daunting challenge, and we will need all the data we can get to make informed decisions about the hard choices coming our way.

Benjamin Twining is a senior research scientist and the vice president for education at Bigelow Laboratory for Ocean Sciences in East Boothbay, Maine. He holds a PhD in coastal oceanography from Stony Brook University.

Photo 1: A satellite photo of the Baltic Sea surrounding Gotland, Sweden, captures algae blooms swirling in the water (European Space Agency).

Photo 2: A NASA satellite image of a phytoplankton bloom — the small red patch in the bottom center of the image — created by adding iron to the North Pacific emphasizes the scale of the bloom relative to productive coastal waters (Institute of Ocean Sciences).