Why Actions for Climate Change May Not Benefit Our Oceans: Exploring the Complex Relationship

Global warming is causing a significant decline in ocean oxygen, with around two percent lost in recent decades. This oxygen loss poses serious threats to marine ecosystems. While it might seem logical that climate solutions would help, a new study shows that many techniques for removing carbon dioxide from the ocean could actually worsen the situation.

Lead author Prof. Dr. Andreas Oschlies from GEOMAR explains, “What benefits the climate isn’t always good for the ocean.” He and an international team assessed various carbon dioxide removal (mCDR) methods using advanced models to understand their impacts on ocean oxygen. Their findings are published in Environmental Research Letters.

The study highlights certain methods, such as ocean fertilization and large-scale macroalgae farming, as particularly concerning. These methods enhance photosynthesis but lead to oxygen-consuming decay when the plant matter sinks. This oxygen loss could far exceed any benefits gained from reducing global warming. In fact, the research suggests that these methods could decrease oxygen levels by four to 40 times more than expected gains.

On a brighter note, some geochemical methods, like enhancing ocean alkalinity with limestone, show minimal impact on oxygen. These approaches resemble simply cutting CO₂ emissions. Notably, only large-scale macroalgae farming with biomass removal can boost oxygen levels overall. By taking nutrients out, this method prevents further oxygen depletion elsewhere. If applied effectively, it might even replenish up to ten times the oxygen lost from climate change. However, this could also reduce biological productivity in the ocean.

In light of these results, the authors stress the need for monitoring ocean oxygen levels in future mCDR initiatives. Oschlies warns, “The ocean is a delicate system. Any large-scale intervention should not threaten marine life.”

As climate policies evolve, Germany, for instance, might still emit significant greenhouse gases in the coming decades, making carbon dioxide removal essential to achieve net-zero emissions. The ocean plays a critical role in the carbon cycle, naturally absorbing CO₂ over extended periods. Targeted mCDR techniques aim to speed up these processes, but understanding their impact on ocean health is crucial.

Recent research highlights that ocean oxygen levels have dropped by about 1.5% since the 1960s, greatly affecting marine life and biodiversity. With species dependent on adequate oxygen, the stakes are high. It’s becoming increasingly important to balance climate efforts with ocean health for a sustainable future.

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