WOR 8 « World Ocean Review

WOR 8

The Ocean – A Climate Champion? How to Boost Marine Carbon Dioxide Uptake: > What action should we take for the effective mitigation of climate change? Measures to avoid greenhouse gas emissions are surely the main priority – but the truth is that in the coming decades, we will also have to remove large quantities of carbon dioxide from the atmosphere and store it securely. Can – indeed, should – the ocean aid us in this task? The new World Ocean Review (WOR 8) explores this issue with reference to the oceans' role in the Earth's carbon cycle and looks at the benefits, risks and knowledge gaps around the main marine carbon dioxide removal techniques.

Urgently sought – ways out of the climate crisis

> We have known for decades that the Earth's atmosphere is warming and the climate is changing, and that this is caused by our emissions of greenhouse gases. Our mindsets, however, have remained unchanged and precious time has been wasted. Only now, with dramatic impacts becoming increasingly obvious, are leaders starting to make serious efforts to find solutions. They are forced to recognize that merely reducing greenhouse gases is not enough to keep climate change within tolerable limits.

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The role of the ocean in the global carbon cycle

> The world ocean is the second largest carbon reservoir on Earth. It stores around 40,000 billion tonnes of carbon. The amount of carbon contained in the ocean exceeds that in the atmosphere by a factor of greater than 50. The ocean and atmosphere, however, are constantly exchanging carbon. With increasing concentrations of carbon dioxide in the atmosphere, more carbon dioxide is absorbed by the ocean, which slows the rate of climate change.

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Harnessing the untapped potential of terrestrial ecosystems

> Terrestrial ecosystems store significantly less carbon than the oceans. Nevertheless, they can make a valuable contribution to the fight against climate change. We must protect existing forests, grasslands and wetlands to this end, engage in large-scale ecosystem restoration and return to sustainable methods of farming and forestry. We've known how to do this for a long time. The only thing that's missing is the will to actually do it.

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Ocean-based CDR – research under massive expectations

> In the search for ways out of the climate crisis, attention is increasingly focused on ocean-based methods to boost the removal of CO2 from the atmosphere. However, much of the knowledge about the potentialities, feasibility and impacts of ocean-based CO2 removal (CDR) is theoretical. Marine research is now expected to deliver solutions as swiftly as possible, but faces criticism, as well as competition from businesses whose primary goal is to generate revenue from ocean-based CDR.

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More carbon sequestration in marine meadows and forests?

> Tidal marshes, seagrass meadows, mangrove and kelp forests cover far less than one per cent of the ocean and coastal area, but contribute significantly to natural carbon sequestration in the seabed. Plans to expand these coastal habitats in order to increase their natural carbon dioxide uptake will probably only be successful in particular oceanic regions. Nevertheless, they may well be worthwhile for multiple reasons.

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Artificial upwelling – the idea of greening the ocean

> Algae, zooplankton and fish are prime drivers of what is termed the biological carbon pump. This natural process needs nutrients to function properly. Such nutrients, however, are lacking in many places, notably in sunlit surface waters. Pumping up nutrient-rich deep ocean water could remedy this nutrient deficiency. Whether such a step would actually increase the ocean's natural uptake of carbon is uncertain.

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Targeted interventions in marine chemistry

> Complex processes allow the ocean to absorb carbon dioxide from the atmosphere, chemically bind much of the carbon it contains, and store this carbon in its water masses. However, the more carbon dioxide the sea absorbs, the more acidified its waters become. This process could be reversed through a targeted boost of its natural acid-binding capacity. As yet, however, little is known about the impacts that could result.

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Injecting carbon dioxide deep beneath the sea

> When carbon dioxide is captured during industrial activities or is removed directly from the atmosphere, the question of appropriate storage arises. Because underground land-based storage sites harbour risks and provoke protests from local communities, the search for storage options in rocks deep beneath the sea is intensifying. The technology for this already exists and has been employed for decades in various pilot projects.

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Key principles and rules for the use of marine CDR procedures

> There is no longer any doubt that humanity must remove carbon dioxide from the atmosphere if it is to achieve its climate targets. However, this removal must meet exacting requirements: neither nature nor people should be harmed, and the removal should be permanent and have a positive climate impact at the same time. Initial propositions, principles and regulatory approaches have already been developed, but the debate has only just begun.

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