Ocean Carbon Removal: Is it Really the Answer to the Climate Crisis?

By now we are all aware of the climate crisis and the impact of our uninhibited release of greenhouse gases. The more we research and learn about this topic, the more concerned scientists become that simply cutting down on our fossil fuel use and limiting carbon dioxide emissions won’t be enough to save our planet from irreversible damage. As a consequence, some scientists now believe that we will also need to start actively removing carbon dioxide that has already been emitted. Of course, this has been taking place for decades in the form of reforestation but now we are also testing more technological options such as direct air capture. With many potential land-based solutions already trialled, researchers, innovative businesses and national governments are now looking to the oceans to save us. Most governments have already cited carbon dioxide removal in their long term plans to mitigate climate change but America and Japan have specifically spoken about their intent to remove carbon from the ocean. There has also been a significant increase in funding for companies in this new industry but just what does removing carbon from the ocean really mean? What is the process, does it work and will it really have a positive impact on our planet?

There are a range of ocean carbon removal techniques which are currently being trialled and tested around the world, some more invasive or innovative than others. Overall however, most aim to enhance or accelerate the natural processes which already happen in the ocean. Our seas are in fact a brilliant carbon sink, having already absorbed 30% of all carbon dioxide emitted by humans. They actually hold an astonishing 42 times more carbon than our atmosphere does. However, taking in all this additional carbon has left its mark on our oceans as they become increasingly acidic, impacting a range of species, in particular molluscs which struggle to build their protective shells in these conditions. Since the boom in carbon emissions, our oceans are also suffering a loss of oxygen and unbalanced nutrient cycles as the chemistry of the water is altered. All of these factors are affecting the delicate marine ecosystem and its interwoven food web.

The ocean carbon removal techniques which focus on enhancing natural biological processes tend to be less technical solutions, such as the restoration of coastal wetlands, including mangroves, seagrass meadows and intertidal marshes. These ecosystems are actually incredibly efficient carbon sinks which see plants absorb carbon dioxide in order to grow before transferring it to the soil where it is locked in by their tangled roots. As long as we leave these ecosystems alone and don’t start digging them up for drainage ditches or development, this carbon can remain in the ground for thousands of years. Despite their blander appearances, these incredible natural systems actually absorb twice as much carbon dioxide as our tropical forests which have received a lot more conservation attention. 

The cultivation of seaweed and the growth of seaweed farms is also a way communities around the world are trying to boost carbon sequestration as well as creating a new source of income. Currently, all the existing seaweeds in the world store 175 million tonnes of carbon dioxide, the equivalent of 10% of the world’s car emissions! By planting new beds of seaweed, not only can we capture more carbon but we can create a healthier ecosystem for marine species and harvest a product which can be used in food, cosmetics and medicine.

A more scientific method of carbon removal is called nutrient fertilisation which aims to replicate the natural biological carbon pump which works in the ocean. It sees us add nutrients, such as iron, to the ocean which in turn fuels the growth of phytoplankton, a microscopic algae. An increased number of algae then absorb carbon and convert it to biomass. This is then passed through the food chain and eventually sinks down to the seabed in the form of faeces or dead creatures. Once in the deep ocean, it can be stored here for thousands of years. Whilst the science behind this makes sense, many are concerned about the effect of dumping large quantities of nutrients in the ocean and how it would affect the delicate balance of the ecosystem which has slowly evolved over millions of years and may not adapt well to sudden changes. For example, whilst iron will fuel a boom in phytoplankton growth, it could also cause an increase in harmful algal blooms which negatively affect many marine species by blocking sunlight and depleting oxygen reserves. The production of iron is also incredibly carbon intensive, leading some to question whether this process may emit more carbon dioxide than it removes.

At the most extreme end of the scale are two other technologies currently battling for funding and the chance to try their ideas on larger scales. The first sees electricity being used to separate seawater into acidic and basic solutions. The acidic solution is then used to remove carbon dioxide from the ocean where it will be stored out of the atmosphere. Currently, scientists believe there is a large potential to store carbon deep under the Earth’s surface in rocks.

The second of these is alkalinity enhancement which has recently received funding from several governments and grant schemes. In particular, one Canadian company is pushing forward with trials, two of which are in Canada and one in Cornwall, England. Their trial for ocean carbon removal sees magnesium hydroxide added to the wastewater pipe that flows into St Ives Bay. The science states that magnesium hydroxide will work to reduce the acidity of the water by removing carbon dioxide, allowing the ocean to have the capacity to absorb even more of our carbon emissions. This particular site has been chosen specifically because of its special geography of a shallow bay with turbulent water which will allow chemicals to remain in the upper layer for longer. However, it is the very uniqueness of this site which has seen 300 protestors line its shores. This area of Cornwall is especially rich in wildlife, home to a globally important population of Atlantic seals as well as dolphins, seabirds and quite often passing basking sharks and humpback whales. The bay also contains some heavy metals as a legacy of Cornwall’s mining past which locals are worried may have a dangerous reaction to any added chemicals.

A trial took place in the area last autumn with very little public knowledge and their results found that the patch of ocean near the waste pipeline did decrease in acidity whilst carbon dioxide in water 10 metres from the pipe also declined. However, the trial did not study any biological impacts, such as whether the chemical had a toxic impact on local marine species. With another 120 day trial planned for this summer, locals are pushing hard for them to be consulted on the work and for an environmental impact assessment to be carried out. If the trial is unsuccessful and is found to have damaging impacts, not only will the surrounding wildlife be harmed but the local economy, which relies heavily on tourism and fishing, could suffer. There is also the argument that the very basis of this model is unsustainable, with magnesium hydroxide currently mined in China, shipped to America for grinding and then shipped to the UK for use, creating an enormous trail of carbon dioxide emissions which it then has to offset before it can have any positive impact. 

This example clearly highlights what many are questioning about all carbon removal techniques; are we solving one environmental problem and creating another? If magnesium hydroxide does help our oceans store more carbon, are we then going to run out of this element and create gaping holes in what was a natural environment in order to mine more? What if we pour iron into our oceans to accelerate phytoplankton growth but accidentally fuel algal blooms which suffocate our diverse underwater habitats and lead to a loss in biodiversity? What if we use electricity to pump carbon dioxide out of the ocean but actually continue to use fossil fuel based energy to do so and create a new source of emissions? Even if these technologies work there is also the question of how long will they store our carbon for? And with each local ecosystem being unique, will the success and side effects vary between them all? Can we even remove enough carbon dioxide to make a difference?

So many questions are left to be answered before we push ahead with schemes that are designed to manipulate the ocean’s natural system which has evolved so delicately and precisely over millions of years. We still have so much to learn about the world that we cannot be certain of the complex, interconnected knock-on effects our actions will have in ten, fifty or one thousand years. At the moment, our laws which govern the seas are not set out to cover the impacts of carbon removal attempts, only the effects of issues such as pollution and dumping. If we want ocean carbon removal to make a significant difference, we will need to work in the high seas, areas which are not owned or protected by any one country. Therefore, it is essential we set up an international agreement which dictates how we jointly fill in gaps in our knowledge, carry out accurate and transparent research and involve a wide range of stakeholders, not to mention how we monitor the process to ensure no negative impacts go undetected. We still have a long way to go before carbon removal can be considered an everyday technology but it is up to everyone to ensure that these ventures really do benefit the environment and not just a businessman’s pockets or a multinational company desperate for carbon credits.

By Neve McCracken-Heywood