Search for a Second Chance

Society is failing to curb greenhouse gas emissions, and climate change is rapidly altering the planet. Immediate action is needed, but it is likely too late for emission reduction alone to halt the significant consequences of two centuries of pollution. However, ocean science may give us tools to turn back the clock.

Our planet has an amazing variety of ways it removes carbon dioxide from the atmosphere, and Bigelow Laboratory scientists are joining researchers around the world to find ways to amplify those natural processes. From fertilizing marine plant growth to restoring vital ecological communities, the Laboratory’s researchers are exploring solutions that might complement emission reduction to keep us below critical thresholds.

“Humans haven’t shown the political will to cut their emissions,” said Senior Research Scientist Ben Twining. “Even if we were to turn off the spigot of carbon dioxide right now, there’s already enough in the atmosphere that warming is baked into the climate system. We need to actually take some carbon dioxide out of the equation.”

Removing carbon dioxide from the atmosphere is now essential to meet the Paris Agreement’s targets according to an April report from the Intergovernmental Panel on Climate Change. Despite the unknown efficacy or consequences of the yet-to-be determined methods, governments worldwide are counting on them to avert disaster. Research is urgently needed to explore the potential solutions — and prevent uninformed decisions from causing unintended consequences.

Scientists are looking at a suite of approaches that build on natural ocean processes to take carbon out of the atmosphere and store it for long periods of time. Bigelow Laboratory researchers are working around the world to study five leading approaches and build the understanding needed to guide global decision making in the near future.

“I want to help equip society to make the best possible decisions,” Twining said. “The earlier we start working on these problems, the more options we’ll have. I want to do my part to work on solutions, and we can’t afford to wait.”

1. Ecological Restoration

The ocean removes billions of tons of carbon from the atmosphere annually, where much of it is then stored for hundreds or thousands of years. Despite making up less than two percent of the global ocean, coastal habitats sequester about half of this “blue carbon” by locking it away in sediments.

Coastal development and climate change are putting immense pressure on these precious ecosystems, which are contracting by an average of one to two percent each year. As they shrink, so does their ability to remove and store carbon. And once they’ve degraded, they release that carbon back into the environment. About a billion tons of carbon dioxide is currently released this way each year.

Globally, most of the recognized coastal blue carbon is in mangrove, salt marsh, and seagrass ecosystems. In the Gulf of Maine, seaweed beds, such as kelp forests, may also be a blue carbon sink, but research is needed to determine if managing and conserving them would be an effective way to remove carbon from the atmosphere.

“Kelp forests grow amazingly fast, take up a lot of carbon in the process, and skirt our coast for hundreds of miles,” said Senior Research Scientist Doug Rasher. “It’s really urgent that we figure out how much blue carbon is produced by Maine’s vast kelp forests to understand their potential for carbon removal.”

Rasher recently completed a two-year kelp forest survey to evaluate their health in the warming Gulf of Maine — a first step toward determining their current and potential blue carbon contribution. His research revealed lush kelp forests in the cold, northern reaches of Maine, and an almost complete collapse of the forests in the south.

“Maine’s kelp forests are changing right before our eyes,” Rasher said. “If we’re going to manage and conserve wild forests with the aim to remove atmospheric carbon, we first need to understand how these forests are changing, why they are changing, and what these changes mean for blue carbon.”

This potential ultimately relies on how much carbon is being locked away in long-term sediment storage, rather than being released when the seaweed breaks down. Tracking its fate is logistically challenging, and Rasher has started by collaborating with other researchers to study the process at seaweed farms.

2. Seaweed Farming

Seaweed cultivation is a promising approach to carbon dioxide removal with direct benefits for society. Bigelow Laboratory scientists are leading worldwide efforts to support the developing industry while helping the planet.

“Existing seaweed farming practices could be modified to enhance carbon removal and storage, while also generating a nutritious crop in an increasingly food-insecure world,” said Senior Research Scientist Nichole Price. “Seaweed farming is a rapidly growing industry with the potential to help combat climate change, while helping working waterfronts adapt.”

Kelp absorbs carbon from seawater as it grows at farms. Some of this carbon could be removed from the global carbon cycle when fragments of the kelp fall to the seafloor and get buried in the sediment below.

However, scientists are unsure how much carbon is sequestered through these processes and how long it stays locked away. Price is working with Rasher and Senior Research Scientists David Emerson, Manoj Kama- lanathan, and Peter Countway to answer those questions using DNA in the environment.

“If we can identify a unique genetic signal of kelp in the sediment below kelp farms, we could use it to determine kelp’s potential for carbon storage,” Countway said. “We don’t yet know exactly what signal we should be looking for, but that’s part of the challenge and excitement of scientific research.”

In addition to its potential role in carbon dioxide removal, seaweed has gained interest for use by a wide variety of industries. Price is also working with partners to explore how the energy-efficient crop could be used in ani-mal feed, bioplastics, and fertilizers, thereby avoiding carbon dioxide emissions elsewhere in supply chains.

Farming seaweed at a scale large enough to make a global impact on carbon levels will be challenging, as it would require many millions of acres. However, it will likely prove to be a valuable strategy at smaller scales, providing a resource for carbon credit programs while producing a harvestable product for coastal communities.

3. Ocean Fertilization

Phytoplankton are responsible for most of the transfer of carbon dioxide from the atmosphere to the ocean, together removing as much as plants on land. When they die, some of this carbon sinks and is stored in the deep ocean and sediment.

The number of phytoplankton in the ocean is generally limited by the amount of key nutrients in the water. In the Southern Ocean, the most important region for carbon dioxide removal, iron is the limiting resource. Research has shown that adding small amounts of iron to surface waters triggers phytoplankton growth. If done at large scales, this could enhance the natural process of carbon transport to the deep sea.

“We know nutrient fertilization amplifies carbon dioxide removal, but we don’t fully understand its impact,” Twining said. “We need to learn how efficient the process is, how long that carbon is removed for, and how adding nutrients might change ocean ecosystems.”

Life in the ocean has responded positively to increased nutrients in the past. Almost 20,000 years ago, there was 20 times more nutrient-rich dust going into the Southern Ocean than now, which fertilized a more productive marine community. During the Australian wildfires in 2019 and 2020, nutrients from smoke also fertilized the Southern Ocean — causing phytoplankton blooms that removed billions of pounds of carbon from the atmosphere.

Twining is investigating the nutrient compounds that could most efficiently provide iron, as well as how fisheries might be affected. Senior Research Scientist David Emerson is a collaborator on several related projects, including one to calculate the cost of iron fertilization per tons of

carbon removed under several possible scenarios. Emerson is also investigating bacteria that produce nanoparticles of iron that could be used in nutrient compounds.

Since the 1990s, scientists have conducted intermittent fertilization experiments but much remains unknown about its scalability and broader impacts. Increasing phytoplankton, a key species in ocean food webs, could lead to greater fisheries productivity or greater whale populations. However, this could also lead to overpopulation of phytoplankton, some of which cause harmful algal blooms.

“I’m trying to use my skills to help us reduce atmospheric carbon in the least harmful way, because the cost of inaction will be worse,” Twining said. “I don’t think of myself as a champion for ocean fertilization, but I am a champion for science being used to empower smart decisions about our future.”

4. Artificial Upwelling

Nutrients may not need to be added to the ocean to spur phytoplankton growth. Water from deeper parts of the ocean is generally richer in nutrients than at the surface. Vertical movement of water, called upwelling and downwelling, naturally transfers them between the environments.

As a carbon dioxide removal approach, upwelling could be artificially enhanced to increase the supply of nutrients to the surface ocean. This would increase phytoplankton growth and thereby carbon removal from the atmosphere, similar to the strategy of ocean fertilization. However, there is one important caveat: deep water also has high amounts of carbon dioxide.

“So, while you are pumping up nutrient-rich water, you are also pumping up carbon dioxide,” Senior Research Scientist Steve Archer said. “This has the potential to significantly reduce or cancel out the benefit of more phytoplankton, so finding the balance is key.”

Since the 1950s, researchers have sought to artificially enhance upwelling using pumps and other approaches. Several experiments have shown that the method can deliver deep water to the surface and stimulate a measurable biological response, but the research has been limited to controlled, small-scale environments. Efforts in the ocean have not yet demonstrated that this approach could effectively sequester atmospheric carbon.

Archer is working with international teams to better understand the impacts of artificial upwelling in the environment around the Canary Islands and Peru. His research shows that added nutrients from deep water increased phytoplankton growth more strongly than predicted. The process also led to a large spike in dimethyl sulfide — a gas that helps form clouds, which reflect the sun’s rays and keep the planet cool.

Despite the positive results, Archer thinks artificial upwelling may be better used as a supplementary carbon dioxide removal method. The pumps and infrastructure required would be difficult to deploy on a large-enough scale to draw down atmospheric carbon dioxide.

“Rather than thinking about upwelling as a global solution, it is probably most promising as a targeted strategy for nutrient-starved ecosystems,” Archer said. “It could deliver a pulse of phytoplankton that would locally boost carbon removal and support the foundation of the food web.”

5. Ocean Alkalinization

One of the most promising carbon dioxide removal approaches is perhaps the most ambitious. Archer is also part of an international project to explore the possibility of altering the chemistry of ocean water to absorb more carbon dioxide from the atmosphere.

About a third of the carbon dioxide that humans have pumped into the atmosphere has been absorbed into seawater through chemical reactions. This has changed the character of the ocean, making it more acidic and less able to draw in more carbon.

Research suggests that it is possible to reverse these effects by adding crushed minerals to seawater at a large enough scale to impact global carbon dioxide levels. This “alkalinization” would mimic an acceleration of the natural weathering processes that have balanced the ocean’s chemistry on geologic timescales. The technique has the added benefit of counteracting ocean acidification, which threatens many marine ecosystems and shell-forming organisms.

“You always get winners and losers with these kinds of changes because the ocean is so diverse,” Archer said. “We want to understand which organisms really benefit from this and how detrimental it is to others.”

The team recently simulated alkalinization in the first experiment of its scale with large test chambers in nearshore waters around the Canary Islands, followed by a similar experiment in Norway. Using dissolved minerals to alter the water chemistry, the scientists tested the effectiveness of different treatments and investigated their impacts on marine life.

Even if this strategy is proven to work and the minerals can be effectively dispersed with enough regularity to maintain higher ocean alkalinity, obtaining the needed minerals represents a large hurdle. It would require development of a new mining industry, perhaps one even on the scale of current global cement production.

“The fact that this strategy is being seriously considered speaks to how dire the problem is. Governments and scientists wouldn’t be thinking about these kinds of options if they weren’t confident that dealing with the unmitigated consequences of climate change will be worse,” Archer said. “But, like with renewable energy, it’s important to also see the opportunities

The Path Forward

Regardless of how well any one technique works, scientists believe that no carbon dioxide removal strategy will prove to be a silver bullet. Multiple methods will need to be employed alongside significant reduction in carbon emissions.

“We can’t continue to pump carbon into the atmosphere at the current rate and hope we will eventually capture enough of it to offset our lifestyle,” Rasher said. “We also need to rapidly and dramatically reduce our global greenhouse gas emissions if we are really going to curb the impacts of climate change.”

Scientists around the world are working on research to guide the pressing decisions that need to be made. However, the potential options become fewer and more extreme with each passing year that society fails to meaningfully address carbon emissions.

“The human race has put ourselves in a corner: we’re either going to deal with a world of doubled carbon dioxide concentrations, or we’re going to deal with how we take carbon dioxide out of the atmosphere,” Twining said. “There are good reasons why we might not want to fiddle with the oceans, but I think every strategy should be on the table until we have reasons to take it off. And the way we figure out those reasons is by doing ethical, transparent research.”

Photo Captions:

Photo 1: An experimental setup in the Canary Islands was used by Senior Research Scientist Steve Archer in 2021 to test the effectiveness of different ocean alkalinization treatments and investigate their impacts on marine life.

Photo 2: Tiffany Stephens, chief scientist and research director at Seagrove Kelp Co., examines young kelp.

Photo 3: The addition of scarce nutrients to the ocean has the potential to help remove carbon dioxide from the atmosphere by triggering phytoplankton blooms like the one shown in this satellite image.