Before Making the Ocean Absorb CO₂ — Six Challenges Facing Environmental Monitoring of Marine Carbon Removal

Can the Ocean Absorb CO₂? — Hopes and Challenges at the Frontier of Marine CDR

To reach net-zero greenhouse gas emissions by 2050, technologies that actively remove CO₂ from the atmosphere are needed to offset residual emissions. The ocean is Earth's largest carbon sink, absorbing roughly a quarter of anthropogenic CO₂ — making marine carbon dioxide removal (mCDR) an attractive but complex prospect.

41 Experts from 6 Countries Convene — The CDRmare Workshop

The German marine research mission 'CDRmare' hosted an international workshop at GEOMAR Helmholtz Centre for Ocean Research in Kiel in September 2025. Experts from Germany, Canada, Norway, the UK, the US, and Japan gathered to address the critical question: how do we responsibly monitor environmental impacts of ocean-based CDR field trials?

Six Key Challenges Identified

• No unified guidelines exist for environmental monitoring systems for responsible field trials
• Natural ecosystem variability and other anthropogenic impacts make it difficult to distinguish experimental effects from background variation
• Long-term environmental baseline data is often unavailable but essential for identifying changes
• Computer models have limited ability to predict environmental impacts and define critical thresholds
• Environmental parameters to measure vary by location and removal method, requiring collaborative decision-making among authorities, operators, and stakeholders
• No unified regulations exist for field trials, which are conducted under diverse frameworks at regional, national, and international levels

Our report reveals the enormous challenges facing the monitoring of marine CO₂ removal processes. Scientists must develop reliable monitoring systems and conduct field experiments to bridge the gap between lab results and real-world impacts.

— Prof. Alexander Proelss (CDRmare Co-Chair)

Germany has a dual responsibility: to establish solutions meeting domestic environmental protection requirements while simultaneously promoting international standards for environmental monitoring of marine CO₂ removal through successful best practices.

— Prof. Andreas Oschlies (CDRmare Co-Chair)

For ocean carbon cycling, see "The Deep Ocean's Unlikely Adapters."

What This Means

A domain where 'trial and error' is not acceptable — Lab and mesocosm studies alone cannot reliably predict the effects and impacts of marine CO₂ removal. Yet real field trials face massive challenges in measuring parameters, separating experimental effects from natural variability, and ensuring no lasting harm.

The baseline data gap — 'no baseline to measure against' — Detecting environmental change requires knowing the pre-intervention state. But for many ocean areas, long-term baseline data simply doesn't exist. This problem extends beyond marine CDR to deep-sea mining and other ocean interventions.

Germany's ambition as an 'international model' — The CDRmare project, launched in 2021 and running until July 2027, aims to establish domestic best practices and propose them as international standards, potentially shaping how the world approaches marine CO₂ removal.

環境変化を検出するためには、「介入前の状態」を知る必要があります。しかし多くの海域では長期的なベースラインデータが存在しません。これは海洋CDRに限らず、深海底鉱物資源開発や洋上風力発電など、あらゆる海洋開発に共通する課題です。

ドイツが目指す「国際モデル」としての役割

CDRmareプロジェクトは2021年に開始され、2027年7月まで継続予定です。ドイツは国内でのベストプラクティスを確立し、それを国際基準として提案することで、海洋CDRの責任ある実施をリードしようとしています。日本もメタンハイドレート開発等で同様の課題に直面しており、この動向は注視に値します。