Marine Geoengineering: Potential and Challenges in Combating Climate Change

Climate change is a pressing issue that needs no further introduction. It is now evident that achieving the 1.5°C target set by the Paris Agreement will require not only significant reductions in CO₂ and other greenhouse gas emissions but also active removal of carbon from the atmosphere. Because they absorb about 20% of global CO₂ emissions annually, the world’s oceans attract attention for this carbon removal. Exploring ways to enhance this natural process falls under the umbrella of marine geoengineering. There are several marine geoengineering techniques that aim to increase the ocean's capacity to absorb and store carbon. Amongst others, these include:

 

1. Enhanced Rock Weathering: This process involves adding pulverized rocks to the ocean, where they react with CO₂ to form carbonates, thereby accelerating the natural weathering process of rocks that normally occur in rivers. In addition, this increases the ocean’s alkalinity, enhancing its CO₂ Higher atmospheric CO₂ levels have made oceans more acidic, diminishing their ability to absorb CO₂.
2. Ocean Fertilization: Adding iron or other nutrients to ocean waters stimulates phytoplankton growth. These microscopic plants photosynthesize CO₂ into oxygen and organic matter. When they die, they sink to the ocean floor, sequestering the carbon in deep-sea sediments.
3. Algae Cultivation: Like phytoplankton, algae perform photosynthesis, drawing CO₂ from the atmosphere. Cultivating large amounts of algae could increase carbon sequestration while providing additional benefits such as biofuel production.
4. Artificial Downwelling: This technique involves pumping surface waters saturated with CO₂ into the deeper ocean, replacing them with less saturated waters from below, thereby enhancing the ocean's overall capacity to absorb CO₂. The opposite, upwelling, can be done as well.
5. Direct CO₂ Sequestration includes storing liquid CO₂ in mid-depth waters, on the seabed, or in seabed sediments and depleted oil and gas reservoirs. These methods aim not to enhance the oceans’ CO₂ absorption processes but to store CO₂ directly in the ocean or its sediments, effectively removing it from the atmosphere.

These marine geoengineering solutions promise large climate change mitigation potential, amounting to multiple Gigatons of CO₂ annually[1], by enhancing the ocean's natural carbon sequestration capabilities or directly sequestering carbon in the ocean or its sediments.

Next to enhancing oceans’ CO₂ removal from the atmosphere, other approaches focus on increasing the reflection of solar radiation, which could help cool the planet. This can be achieved by enhancing the albedo, or ability to reflect solar radiation, of the ocean surface by introducing reflective particles, microbubbles, foams, or reflective algal blooms to the surface. Another option is to make clouds above the ocean brighter by adding seawater, as the increased droplet concentration makes the clouds denser and more reflective.

 

However, these marine geoengineering solutions are not without their challenges and risks. These techniques often require substantial amounts of materials, such as rocks or fertilizers, and energy. Moreover, the large-scale deployment of these technologies could have unforeseen consequences that still need to be fully understood. The methods aimed at increasing solar reflection, in particular, alter the solar energy balance without addressing the root cause of increased atmospheric CO₂. This could affect photosynthesis and broader ecological processes.

 

Therefore, geoengineering solutions may have been somewhat overlooked in climate debates so far. Even though continued research is crucial to fully understand their potential impacts and develop safe and effective large-scale implementation strategies, we should wait to write them off. In this gargantuan battle against the changing climate, we must keep our eyes open for every possible solution. Meanwhile, the primary focus should remain reducing CO₂ and GHG emissions to address the root causes of climate change.

 

 

[1] Smith et al. (2024). The State of Carbon Dioxide Removal 2024 - 2nd Edition. DOI: 10.17605/OSF.IO/F85QJ