New Study Assesses Marine Geoengineering Risks and Knowledge Gaps for Ocean Ecosystems

Understanding the Research

As climate change accelerates and political action lags, scientists are increasingly evaluating geoengineering technologies that could help mitigate global warming. A new comprehensive study published in Reviews of Geophysics examines the potential impacts of marine geoengineering interventions on ocean ecosystems, identifying critical knowledge gaps that must be addressed before implementation.

The research, led by Kelsey Roberts from the University of Massachusetts Dartmouth, systematically assessed eight geoengineering interventions most likely to directly impact marine ecosystems. With oceans already storing approximately 25% of anthropogenic carbon emissions, marine-based carbon dioxide removal (mCDR) and solar radiation management techniques represent potentially powerful climate intervention tools.

Marine Carbon Dioxide Removal Methods Under Scrutiny

Biotic Approaches: Harnessing Ocean Life

The study examined several biotic mCDR technologies that utilize photosynthesis to capture carbon and store it in ocean depths. Microalgae fertilization involves adding growth-promoting nutrients like iron to surface waters, stimulating phytoplankton blooms that absorb CO2. Similarly, artificial upwelling pipes deep, nutrient-rich seawater to the surface to boost phytoplankton growth, though this remains largely unproven.

Macroalgae cultivation represents another biotic approach, where seaweed farming produces carbon-rich biomass that descends into the deep sea. However, these methods raise significant ecological concerns. Dense algae blankets could block sunlight from deeper waters, alter nutrient balances between different ocean areas, or create hypoxic zones as decomposing biomass consumes oxygen.

Terrestrial Biomass Storage in Oceans

Researchers also evaluated storing terrestrial biomass like crop residue in deep ocean environments. While avoiding some problems associated with ocean-based biomass cultivation, this approach could still create low-oxygen zones and disrupt nutrient balances. The study identified storage in anoxic basins like the Black Sea as potentially lower-risk, though concerns about toxic sulfide production during anaerobic respiration remain.

Abiotic Methods: Ocean Alkalinity Enhancement

Ocean alkalinity enhancement mimics natural rock weathering processes that allow seawater to react with CO2, storing carbon as bicarbonate or carbonate. Unlike biotic methods, this approach would likely have minimal direct impacts on marine life at experimental scales. The technique could even help counteract ocean acidification while increasing carbon storage.

However, sourcing alkalinity presents challenges. Electrochemical methods require significant energy inputs and proper waste acid disposal. Mining crushed carbonate or silicate rock carries environmental impacts that could offset climate benefits, with risks of introducing toxic materials or excess nutrients into marine ecosystems.

Solar Radiation Management: Cooling from Above

The study also examined solar radiation modification interventions designed to reflect sunlight and cool the planet. Stratospheric aerosol injection and marine cloud brightening could have profound regional and global impacts on climate and precipitation patterns. Notably, these approaches would not address ocean acidification, merely mask warming symptoms.

Some researchers propose using marine cloud brightening to protect coral reefs during heat waves, but this could alter primary production patterns. All geoengineering interventions would require increased shipping and coastal infrastructure, adding additional ecosystem pressures.

Critical Knowledge Gaps and Uncertainties

The research reveals substantial uncertainties across all examined technologies:

• Carbon Storage Measurement: Difficulty quantifying how much captured carbon would be permanently stored
• Ecosystem Interconnections: Limited understanding of how interventions might affect complex marine food webs
• Food Security Implications: Unclear impacts on global fisheries that millions depend on for protein
• Regional Variations: How effects might differ across various ocean environments
• Long-term Consequences: Potential for unforeseen impacts given ocean system complexity

Modeling Limitations and Research Needs

Current understanding relies primarily on modeling studies, but past models were too coarse and lacked relevant parameters for mCDR technologies. While modeling capabilities are improving, significant enhancements are needed, particularly in resolution and ability to predict large-area impacts.

Chris Vivian, co-chair of GESAMP Working Group 41, emphasizes that large-scale interventions affecting vast ocean areas require much more research, especially regarding potential impacts on fisheries and marine life. The pace of geoengineering governance development has also lagged behind climate change acceleration.

Implications for Climate Policy and Action

This comprehensive assessment underscores the urgent need for careful evaluation of geoengineering proposals. While these technologies might offer climate intervention possibilities, they present significant risks to marine ecosystems and global food security. The study emphasizes that geoengineering should not be viewed as a substitute for rapid fossil fuel emission reductions.

The research highlights the ocean’s complexity and interconnectedness, warning that interventions comparable to terrestrial forestation could have far more unpredictable consequences in marine environments. As Tyler Rohr from the University of Tasmania notes, unforeseen impacts could result from ocean system complexity.

Future Directions and Recommendations

The study calls for expanded research efforts including:

• Improved high-resolution modeling capabilities
• Carefully controlled field testing with extensive monitoring
• Development of robust governance frameworks
• Comprehensive risk assessment protocols
• Stakeholder engagement including fishing communities and food security experts

As Roberts concludes, the fundamental question remains: “Do the benefits outweigh the risks?” Answering this requires filling current knowledge gaps through dedicated research while maintaining focus on the primary goal of rapidly reducing fossil fuel emissions.

Conclusion

This landmark study provides crucial insights into the potential risks and uncertainties surrounding marine geoengineering interventions. While these technologies might seem like attractive climate solutions, the research reveals significant knowledge gaps that must be addressed through comprehensive research and careful governance development. As climate change accelerates, understanding these ocean-based intervention options becomes increasingly critical, but must be pursued alongside—not instead of—aggressive emission reduction efforts.

References

Roberts, K., et al. (2026). Marine Geoengineering Ecosystem Risks and Knowledge Gaps. Reviews of Geophysics. Source: Mongabay