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Oceans and climate

Fishing boats on the beach of Nouakchott, Mauritania

Climate change is causing global warming, ocean acidification and rising sea levels. The temperature of the oceans will continue to increase in the 21st century; it is predicted that the sharpest increase in sea surface temperature will occur in tropical and sub-tropical regions. This rise in temperature causes a reduction in the amount of oxygen in the water, resulting in an increase in "dead zones" or areas with very low oxygen levels.

Also, as the oceans become warmer, thermal expansion occurs, causing a rise in sea levels. The additional water from glaciers melting as a result of climate change adds to this rise. Sea levels have already risen by about 20 centimetres in the 20th century – and the rate at which they are rising is increasing all the time. By the end of the 21st century, therefore, if greenhouse gas emissions remain at their present level, a rise of up to one metre is expected. The only way this rise in sea levels can be reined in is if there is a massive drop in emissions very soon.

Oceans – important ecosystems for climate

The oceans play an important role in regulating the global climate. They release huge amounts of oxygen into the atmosphere and absorb a considerable amount of the carbon dioxide emissions that human beings produce. Meanwhile, coastal ecosystems like the mangrove forests in the tidal areas of tropical coastlines absorb and bind between three and five times as much carbon dioxide from the atmosphere as purely terrestrial forest ecosystems. Furthermore, mangroves provide protection from floods and coastal erosion, and therefore play an important role in terms of adapting to the impacts of climate change. Despite their ecological importance, worldwide almost half of mangrove forests have now been destroyed or have been converted, for example into shrimp farms, since the middle of the last century.

Humanity depends on functioning ecosystems. The basis for their functioning is biological diversity. Biodiversity is the only way to guarantee that development and adaptation options for the world’s ecosystems are upheld. These adaptation options are an urgent necessity in the face of climate change, which is in turn putting considerable pressure on the adaptation capacities and possibilities of all organisms.

Global climate change is putting a strain on the marine ecosystem. The warming and acidification of the oceans as a result of climate change is seriously affecting sensitive ecosystems like coral reefs, is threatening stocks of crustaceans and can have negative impacts on the ability of the oceans to absorb carbon dioxide. The projected loss in fisheries revenues as a result of rising sea temperatures is somewhere between 6 and 15 billion US dollars a year.


International processes

In the Paris climate agreement of 2015, protecting the oceans is accorded an important role. However, we are still a long way from understanding all the implications of the threat that climate change poses for the marine environment. For example, we cannot say precisely what it will mean for the overall ecosystem if certain species become extinct. There is urgent need for more scientific cooperation at all levels.

The issue of marine conservation has now moved up the international policy agenda and is finding its way into global and regional agreements. The 2030 Agenda for Sustainable Development has a specific goal, SDG 14, just for marine conservation. The conservation and sustainable use of marine and coastal areas constitutes a global challenge. There needs to be an integrated approach, also including climate action initiatives, in order to effectively achieve the goals of sustainable development.


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