THE CONTEXT: The ocean plays a crucial role in regulating the Earth’s climate, acting as the planet’s “blue lung.” Covering approximately 70% of the Earth’s surface, the ocean is our planet’s most prominent solar energy collector. Its vast expanse and unique properties make it an essential component of the global climate system.
THE DRIVERS:
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- Climate regulation: The ocean influences weather patterns worldwide, affecting precipitation, droughts, and storm intensity.
- Heat distribution: Ocean currents transport heat from warmer to cooler latitudes, helping to stabilize global temperatures.
- Carbon sequestration: The ocean contains about 50 times more carbon than the atmosphere, exchanging nearly 100 billion metric tons annually.
- Oxygen production: Marine phytoplankton produces at least half of the oxygen in the atmosphere through photosynthesis.
ABSORPTION OF ANTHROPOGENIC CO2 EMISSIONS:
The ocean has been a critical buffer against the full impact of human-caused climate change by absorbing a significant portion of anthropogenic CO2 emissions. Recent studies indicate that the ocean has absorbed approximately 30% of human-caused CO2 emissions since the Industrial Revolution.
Mechanisms of absorption:
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- Physical dissolution: CO2 dissolves in seawater, particularly in cold waters at high latitudes.
- Biological pump: Phytoplankton absorb CO2 through photosynthesis; some carbon sinks to the ocean floor when they die.
- Carbon storage: The ocean stores about 38,000 billion tonnes of carbon, over 28 times more than the carbon stored by land vegetation and the atmosphere combined.
- Long-term sequestration: Deep Ocean currents can keep absorbed carbon from the surface for hundreds to thousands of years.
ABSORPTION OF EXCESS HEAT FROM GREENHOUSE GASES: The ocean has been the primary heat sink for the Earth’s climate system, absorbing most excess heat caused by increasing greenhouse gas concentrations:
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- Heat absorption rate: The ocean has absorbed about 89-91% of the excess heat in the Earth’s climate system.
- Quantification of heat absorption:
- Since 1990, the ocean has accumulated more than 2 x 10^23 joules of energy, equivalent to about five Hiroshima bombs exploding every second.
- The ocean has been heating at a rate of 0.5 to 1 watt of energy per square meter over the past decade.
Depth distribution of heat absorption:
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- 0-700 meters: 0.38 to 0.44 Watts per square meter (1993-2022).
- 700-2,000 meters: 0.17 to 0.32 Watts per square meter (1993-2022).
- 2,000-6,000 meters: 0.07 Watts per square meter (1992-2013).
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- Global impact: The total full-depth ocean heat gain rate ranges from 0.64 to 0.83 Watts per square meter applied to Earth’s surface.
- Temperature moderation: Without the ocean’s heat absorption, Earth’s average surface temperature would be around 50°C instead of the current 15°C.
CONSEQUENCES OF OCEAN’S CLIMATE MODERATION:
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- Ocean Acidification: Ocean acidification is one of the most pressing consequences of increased CO2 absorption. Since the Industrial Revolution, the ocean’s pH has decreased by about 0.1 units, from 8.2 to 8.1, representing a 25% increase in acidity. This trend is expected to continue, with projections suggesting a further drop of 0.3 to 0.5 pH units by 2100.
IMPACTS OF ACIDIFICATION
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- Coral reefs are experiencing reduced growth rates and increased vulnerability to bleaching events.
- Shellfish, such as oysters and mussels, face difficulty forming and maintaining their shells.
- Plankton, which forms the base of many marine food webs, are at risk of population declines.
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- Disrupted Biogeochemical Cycles: The ocean’s absorption of excess CO2 and heat disrupts crucial biogeochemical cycles.
- Carbon Cycle: The ocean’s capacity as a carbon sink may diminish. Warmer waters hold less CO2, potentially leading to a feedback loop where more greenhouse gases remain in the atmosphere.
- Nutrient Cycling: Ocean circulation and stratification changes alter nutrient distribution, affecting primary productivity and food web dynamics.
- Oxygen Cycle: Ocean deoxygenation is becoming a significant concern, with global oxygen content decreasing by about 2% since the 1960s.
- Pollution and Harm to Marine Ecosystems: The ocean’s ability to absorb pollutants and excess nutrients is being overwhelmed, leading to Eutrophication, Toxic Algal Blooms, and Plastic Pollution.
- Eutrophication: Excess nutrients from agricultural runoff and wastewater cause algal blooms, leading to oxygen depletion and “dead zones”.
- Toxic Algal Blooms: Warming waters and nutrient pollution are increasing the frequency and severity of harmful algal blooms, which can produce toxins deadly to marine life and humans4.
- Plastic Pollution: While not directly related to climate moderation, the accumulation of plastic waste in the ocean is exacerbating the stress on marine ecosystems already struggling with climate-related changes.
- Alteration Of Ocean Circulation: Ocean temperature and salinity changes affect global ocean circulation patterns. The Atlantic Meridional Overturning Circulation (AMOC) shows signs of weakening, which could dramatically affect global climate patterns. Altered circulation patterns affect the distribution of heat, nutrients, and oxygen throughout the ocean, impacting marine ecosystems and weather patterns.
- Deoxygenation of Marine Habitats: Ocean deoxygenation is emerging as a critical threat to marine life. The area of low-oxygen water in the open ocean has increased by 4.5 million km² since the 1960s. Oxygen minimum zones are expanding, compressing habitats for oxygen-respiring organisms.
MARINE CARBON DIOXIDE REMOVAL (MCDR): Marine Carbon Dioxide Removal (mCDR) refers to a range of approaches that leverage the ocean’s natural capacity to absorb and store atmospheric carbon dioxide. These methods aim to enhance or accelerate the ocean’s carbon sequestration processes to mitigate climate change.
TYPES OF MCDR APPROACHES:
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- Biotic (Nature-based) Solutions: Biotic approaches utilize living organisms and ecosystems to capture and store carbon dioxide.
- Mangroves and Macroalgae: Mangroves and macroalgae, such as kelp forests, are highly effective at sequestering carbon. Mangroves can store up to 10 times more carbon per hectare than terrestrial forests. Macroalgae, particularly kelp, can grow up to 2 feet per day, rapidly absorbing CO2.
- Carbon Sequestration: The carbon sequestration potential of biotic solutions is significant but limited. Mangrove restoration could potentially sequester up to 0.2 gigatons of CO2 per year, and macroalgae cultivation and sinking could sequester 1-10 gigatons of CO2 per year.
- Abiotic Techniques: Abiotic approaches manipulate the ocean’s physical and chemical properties to enhance CO2 absorption and storage.
- Biomass Burial at Sea: This technique involves growing biomass on land or in coastal areas and then sinking it into the deep ocean. It has the potential to sequester 7-22 billion tonnes of CO2 per year.
- Challenges include ensuring long-term carbon storage, potential impacts on deep-sea ecosystems, and transportation and sinking energy costs.
- Ocean Alkalinity Enhancement (OAE): OAE involves adding alkaline materials to seawater to increase its capacity to absorb CO2. Methods include adding minerals like olivine or using electrochemical processes to increase alkalinity. It has the potential to sequester 1-15 billion tonnes of CO2 per year.
CHALLENGES OF MARINE CARBON DIOXIDE REMOVAL (MCDR):
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- Public Perception and Skepticism: Research indicates mixed public perceptions, with concerns about environmental impacts and the “unnatural” nature of some techniques. For example, ocean fertilization and alkalinity enhancement are viewed less favorably than land-based solutions like afforestation.
- Regulatory Challenges: Ocean interventions’ remote and global nature complicates regulation. Existing frameworks may not adequately cover new technologies like mCDR. Reliable measurement, reporting, and verification (MRV) systems ensure that mCDR activities achieve their intended climate benefits without adverse ecological impacts.
- Energy Use: Techniques such as ocean alkalinity enhancement involve mining and processing minerals, which can be energy intensive. This raises concerns about the overall carbon footprint of these methods.
INDIAN CONTEXT AND POTENTIAL: India’s vast marine resources hold significant potential for marine carbon dioxide removal (mCDR). The Indian Ocean offers promising opportunities for deep carbon burial and other mCDR strategies.
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- Indian Ocean’s Promise for Deep Carbon Burial: The Indian Ocean, along with its sub-regions like the Bay of Bengal and the Arabian Sea, is identified as a potential site for deep carbon burial. Researchers from IIT Madras have highlighted the feasibility of storing CO2 in these regions:
- CO2 Storage Mechanism: This process involves storing CO2 in liquid pools or solid hydrates at depths beyond 500 meters. Due to the gravitational and permeability barriers provided by subsea sediments, this method ensures that CO2 remains trapped without re-emission into the atmosphere.
- Environmental Safety: Storing CO2 at such depths minimizes the risk of harming marine life, making it a viable option for large-scale sequestration efforts.
- Sequestration Estimates: Studies have shown that the Bay of Bengal alone could potentially sequester several hundred gigatonnes of CO2. This capacity is equivalent to several years’ worth of India’s greenhouse gas emissions4.
- Global Contribution: If effectively harnessed, the Indian Ocean could play a crucial role in global efforts to capture 25-40% of marine CO2, significantly contributing to international climate goals.
- Mangroves and Coastal Wetlands: India has extensive mangrove forests, particularly in regions like the Sundarbans. These ecosystems are highly efficient at capturing and storing carbon, providing additional avenues for nature-based solutions.
- Research and Development Needs: There is a need for increased research into these ecosystems’ potential. Initiatives could include enhancing mangrove restoration projects and exploring innovative methods like macroalgae mariculture.
THE CONCLUSION:
The careful study of geological and ecological methods offers a chance to harness the power and vastness of oceans for carbon capture, but success hinges on rigorous science, robust governance, and societal trust. Harnessing these natural systems in the fight against climate change could provide a critical edge, turning the tide on runaway warming while unlocking a powerful, underutilized climate solution.
UPSC PAST YEAR QUESTION:
Q.1 Discuss the causes of depletion of mangroves and explain their importance in maintaining coastal ecology. 2019
Q.2 What are the consequences of spreading of ‘Dead Zones’ on marine ecosystem? 2018
MAINS PRACTICE QUESTION:
Q.1 Discuss the ocean’s role as a critical component in moderating Earth’s climate and the potential of Marine Carbon Dioxide Removal (mCDR) strategies. Evaluate the opportunities and challenges associated with implementing mCDR in the Indian context.
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