Plastic is a good carbon sink

Oceans in a climate crisis

A regulating and stabilizing force in our climate system is coming under increasing pressure

The oceans are victims of global warming and our greatest hope at the same time. As the stabilizing force of our climate system, they store heat, control the weather and are the most important carbon sink on our planet. Your protection can be crucial for the future of all of us.

Dune - Photo: Frank Derer

The oceans cover 71 percent of the earth, make up 95 percent of the living biosphere and contain 97 percent of all water on our planet. Our life today would be inconceivable without the complex structure of the world's oceans made up of water bodies and flow systems, without their productivity, their cycles and interactions with the atmosphere. But their ecosystem services are increasingly at risk.

Since 1970, the oceans have absorbed more than 90 percent of the sun's thermal radiation. They store 50 times more greenhouse gases than the atmosphere and thus 20 to 30 percent of the carbon dioxide produced by humans worldwide since 1980. This makes them our most important natural carbon sink. 93 percent of the world's carbon dioxide goes through the marine carbon cycle. And as a by-product, so to speak, they provide 50 percent of our oxygen, which means that every second breath comes from the sea.

The oceans are gigantic CO2-Depots

Like forests, the plants in the sea - phytoplankton, algae or seaweed - build biomass from carbon dioxide. This removes large amounts of carbon from the atmospheric cycle. In a second mechanism, the physical carbon pump, cold surface water saturated with carbon dioxide takes large amounts of the greenhouse gas with it into the depths for decades.

The consequences of the climate crisis have long been visible in the seas. The rising temperatures threaten numerous species and lead to habitat loss. The rise in sea level today is mainly due to the expansion of the water caused by heat. As more glaciers and ice caps melt on land, this will further accelerate the rise. Floods and flood disasters are the result. Another effect is the acidification of the oceans: when carbon dioxide dissolves in the water, it forms carbonic acid.

The Intergovernmental Panel on Climate Change (IPCC) is sounding the alarm

In September 2019, the Intergovernmental Panel on Climate Change (IPCC) published its interim report on the oceans. New facts and figures make us aware of the drama of the climate crisis, ecologically and economically. But the report also shows what role the seas are playing in overcoming the crisis and what we can do to protect them.

Facts and messages from the IPCC Report 2019:

• The rate of ocean warming has doubled since 1993, with intensifying effects for cyclones and rains.
• The Arctic ice has shrunk by 12.8 percent over the past few decades.
• The melting of ice sheets can lead to a sea level rise of 40 centimeters to over a meter by the year 2100. The water temperature can rise up to three degrees Celsius and the pH can drop to around 7.7.
• The permafrost soils are thawing and threatening to release up to 1,600 gigatons of carbon.
• Warm surface water leads to stable stratified bodies of water and hinders fundamental exchange processes in the sea. Oxygen-poor zones have increased by three to eight percent worldwide since 1970.
• Since the 1950s, the range of many marine species has shifted by up to several hundred kilometers, with negative consequences for fisheries and regional food security.
• While overall biomass production and habitat quality are declining, harmful algal blooms occur earlier in the year and are more pronounced around the world.
• Ocean acidification and decreasing oxygen levels affect current systems and important upwelling areas.
• Coastal vegetation, mangrove belts and salt marshes have declined by 50 percent in the 20th century and are losing their natural coastal protection function. Stocks of seagrass meadows and algae forests have declined by over 40 percent.
• Almost all warm water corals threaten to disappear when the sea warms up to less than two degrees Celsius.

What must we do for the seas?

  • The administrative structures for the protection and use of the seas must be standardized and geared more closely to the threat posed by the climate crisis.
  • A coherent network of well-managed marine protected areas can improve the resilience of the seas and secure ecosystem services.
  • The restoration of mangroves, seagrass meadows and coral reefs must be promoted.
  • In the use of marine resources, especially in fisheries, the precautionary principle should be applied more strongly with a view to the climate crisis.
  • The functions of mangroves, marshes and seagrass meadows as carbon sinks and natural coastal protection must be strengthened.

Seas and climate protection in Germany

The climate crisis has also reached our coasts. The stocks of cod and herring in the Baltic Sea are on the verge of collapse. For example, the spawning behavior of the herring, which is determined by temperatures, and the light-dependent occurrence of phytoplankton have decoupled. The young herring larvae find too little food because the development of the zooplankton follows the phytoplankton and occurs late. The cumulative overloading of the seas is also visible in the North and Baltic Seas, and the Natura 2000 network of protected areas has not been implemented effectively enough.

Windwatt am Darss - Photo: Stella Mielke /

For some years now, offshore wind power has been part of the energy transition and as a new form of use in the sea. But it is not without risk either. The case of the Butendiek wind farm west of Sylt shows us what can happen with poor planning.

The greatest challenge is to understand the climate crisis and the species crisis as a common and indivisible task. Healthy ecosystems, whether seas, moors or forests, with their natural functions, are one of the most powerful weapons against global warming. Renewable energies must also be expanded. However, this must take place within the framework of the ecological load-bearing capacity, i.e. the load limits of the systems, in order not to endanger natural climate functions. In this way, Germany can make an important contribution to containing the climate crisis and the energy transition can succeed. A discussion about overarching questions about lifestyles, sufficiency and efficiency also plays a decisive role.

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