By Towseef Hassan
The ocean, rightly called “the blue lung of the planet”, is central to reducing greenhouse gases (GHGs) and moderating the planet’s climate. The fifth assessment report by the Intergovernmental Panel on Climate Change (IPCC) in 2013 revealed that it has thus far absorbed 93% of the excess heatgenerated by greenhouse gases (GHGs) and 25% of anthropogenic carbon dioxide emissions. Also, the ocean holds 50 times more carbon than the atmosphere. These supporting services in the ocean have largely preserved the humankind from the catastrophic impacts of climate change. The oceans actually put the brakes on how fast the planet is warming by absorbing excess amounts of heat.
While acting as a buffer against the worsening effects of climate change, many threats and disruptions to the ocean health have occurred : changes in water temperature, oceanacidification, disrupted biogeochemical cycles, rising sea levels, alarming damage to coastal and marine ecosystems. Ocean acidification, for example, inhibits the ability of marine organisms like corals, shellfish, and plankton, to build their shells and skeletal structures. These disruptions exacerbate the services the oceans provide- from fisheries to carbon sequestration.
As the world is set to embark on an ambitious journey to achieve a NET ZERO EMISSION limiting global warming to 1.5oC (2.7o F) by 2050, there are accelerating advances in the deployment of clean energy, electric vehicles, and decarbonization. Land-based efforts involve using our land resources to help reduce the harmful effects of climate change. These strategies involve planting trees and protecting forests, wildlife corridors and biodiversity conservation, replacing fossil fuels with BECCS (bioenergy with carbon capture and storage) and biochar, the latter technique is more feasible in wealthier countries because it requires robust technology and climate financing. Despite all our efforts to invest heavily on land, studies reveal that the land is saturated and can no longer support efficient carbon capture.
Marine Carbon Dioxide Removal (mCDR) is one such potentially efficient and powerful new technologies to help emission reductions and removing carbon dioxide concentration in the atmosphere or in the upper ocean. Given the enormous surface area and unique chemistry of the ocean, makes it a focusing and tempting venue for addressing this lingering issue by using careful engineering.
Oceans and other deep-water bodies are good at sequestering excess carbon from the atmosphere transporting the carbon into its depths where it mixes with minerals. Marine carbon capture techniques have been classified into two categories: Biotic methods utilize living organisms like mangroves, seagrasses, algae, and microorganisms to capture and store carbon dioxide. It also involves Phytoplankton Fertilization (phytoplankton absorbs CO2 through photosynthesis and deposit at the ocean bed when they die, sequestering carbon). While Biotic methods are natural and in harmony with biodiversity conservation and well established, their capability of carbon capture is limited and moderate. Abiotic methods, on the other hand, harness the physical or chemical properties, or geological processes for carbon sequestration. Abiotic method offers greater potential of carbon capture and permanence than Biotic technique. For example, biomass burial at sea can capture 7 to 22 billion tonnes of CO2 per year. Ocean Alkalinity Enhancement (OAE), enhances carbon dioxide absorption by increasing the water’s pH and reducing the acidic nature of the oceans. In this technique, alkaline materials (crushed limestone) are added to sea water to neutralize its carbon dioxide content, locking the carbon for thousands of years, effectively sequestering carbon dioxide.
To put all this in perspective, if we promise to avoid the worst climate impacts, global greenhouse gas emissions need to be slashed in half by 2030 and reach NET-ZERO around mid-century. A number of countries have already committed to reach NET-ZERO by 2050. Abiotic methods implemented to potentially enhance the oceans’ ability to sequester more carbon content are shrouded with the blanket of scepticism, and other challenges in terms of investing huge climate financing.
Marine Carbon Dioxide Removal(mCDR)techniques, whilepromising in combating climate change, comes with uncertainties and several potential negative effects and risks. For example, stimulating Phytoplankton growth to capture carbon dioxide, can disrupt other ecosystems, harming marine life. Also, OAE technique has concerns for changing local water chemistry, harming marine biodiversity and sensitive species like corals and shellfish. Biotic techniques are preferred due to their lower environmental risks and greater promise of biodiversity restoration.
Regarding mCDR, fundamental issues remain unanswered about the environmental impacts of different interventions, their cost and safety, and the durability of carbon sequestration. Currently, Global carbon dioxide emissions are approximately 40 billion metric tonnes per year (as of 2023), mCDR methods would need to scaleup drastically to offset this level of emissions. Success hinges on continued scientific research, and public trust, and vigorous governance.
The author works as a lecturer with the School Education Department
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