The main conversation around climate change focuses primarily on one thing: how much carbon is in the air – and by extension how to reduce it. However, what is less talked about, but which can become incredibly important, is how much carbon there is in our oceans. There is 50 times more carbon in the ocean than in the atmosphere. Some climate scientists believe that if we could just slightly increase the amount of carbon the ocean can absorb from the atmosphere, we could avoid some of the worst effects of climate change.
It may seem unusual when you first hear it, but think about it a little longer. The ocean covers approximately 70 percent of the Earth’s surface, and it naturally absorbs carbon dioxide – and effectively dissolves it. Phytoplankton in the ocean use this carbon dioxide and sunlight to drive photosynthesis just like land-based plants. Oxygen is produced by this process – phytoplankton are actually responsible for about 50 percent of the oxygen in our atmosphere.
Some climate scientists have suggested that if we could just increase the amount of phytoplankton in the ocean, we could pull more carbon out of the atmosphere. A well-known way to produce a phytoplankton bloom is to introduce iron, an essential nutrient for the plankton community, to the water. Many parts of the ocean are low in iron, so even a relatively small addition of iron could theoretically produce a lot of phytoplankton and thus remove a lot of carbon dioxide from the atmosphere.
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“Give me half a tanker of iron and I’ll give you an ice age,” wrote John Martin, an oceanographer at Moss Landing Marine Laboratories, in 1988. Back then, most people were just getting to know the idea. climate change as we know it now. But that’s also around the time people started thinking about how iron fertilization could affect phytoplankton growth and in turn change atmospheric carbon levels.
Although climate scientists have spent a lot of time discussing this strategy among themselves, there has not been a concerted effort to explore it further and take it seriously. Ken Buesseler, a marine radiochemist at the Woods Hole Oceanographic Institution, is a researcher who has researched iron fertilization in the ocean. He and his team looked at whether introducing iron could “change the carbon flow to the deep ocean” and found that there was a significant carbon sequestering effect.
Buesseler told The Daily Beast that his research was done almost 20 years ago, and it hasn’t been much since.
“What happened 20 years ago is we started going around and we would spread out a chemical form of iron and look for that phytoplankton – the plant response – and it actually showed very clearly that if you improve the iron, you can create more uptake of carbon dioxide,” Buesseler said. “The difference between now and 20 years ago is that I think the climate crisis is so much more apparent to the public.”
A phytoplankton bloom off the coast of Iceland, as observed from space.
Using the oceans to combat climate change has become a hotly debated topic among climate scientists in recent years, and Buesseler was part of a group of scientists who released a report through the National Academies of Sciences, Engineering, and Medicine late last year that looked at the the options available, including increasing phytoplankton levels.
“We have a large reservoir. It already absorbs a third of greenhouse gases. The question that people are now asking more is what can we do to improve it?” Buesseler said. “Let’s get out there. Let’s do experiments.”
The experiments themselves would not cause damage to the ocean’s natural ecosystem, Buesseler said, but they could tell us a lot about how introducing more iron to the ocean on a much larger scale could affect that ecosystem in the long term. He doesn’t think doing this on a large scale will cause significant harm, but it’s important to get the research done so we can know for sure. He said a “very conservative” estimate would be that up to a gigatonne of carbon dioxide could be sequestered each year if this process were carried out on a large scale.
“It will change the types of plants and animals that grow, but that’s already happening with the changes in temperature and acidity,” Buesseler said.
David Siegel, a professor of marine science at the University of California, Santa Barbara, told The Daily Beast that iron fertilization would also be fairly easy to do. You can simply get a 120 foot fishing boat and start putting the iron where it will be most effective in stimulating phytoplankton growth.
– It can be done relatively cheaply. Every iron atom you add in the right places can cause tens of thousands of carbon atoms to fix,” meaning absorbed by the water. “It’s pretty effective,” Siegel said. “You can put out vessels that release iron oxide into the water—even just iron ore into the water—and you can make flowers that you can see from space. We know that.”
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The effects would happen quite quickly. Scientists who have introduced iron into seawater in the past have seen that phytoplankton blooms can start to become visible within the first 24 hours. The ideal place to introduce the iron would be where it is least abundant, which would be parts of the ocean – primarily in the southern hemisphere – that are not close to land. Iron that ends up in the sea typically comes from dust blown into the sea from land.
Both Buesseler and Siegel emphasized that this should not be seen as an alternative to ending the use of fossil fuels. It remains critical when it comes to having a chance to beat climate change. But to avoid the worst effects of climate change, the development of carbon removal strategies will also be required to reduce the load of greenhouse gases in the air.
“Even if we decarbonize our economies, there are still 20 or so gigatons of carbon dioxide that need to be removed from the atmosphere to stay close to the Paris Agreement goals,” Siegel said.
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