Since the 1970s, the ocean absorbed 90% of human-emitted heat, distributed globally by massive currents, regulating temperatures and weather. It acts as a colossal carbon sink, annually exchanging 90 billion tons of carbon. This buffer mitigates human-induced global warming, yet the ocean's capacity is finite. Human activities, causing destruction and pollution, profoundly impact the ocean and its ecosystems. Climate change intensifies these threats. A healthy ocean, rich in biodiversity and biomass, is essential for sustaining vital climate functions. Therefore, protecting the ocean is synonymous with climate protection.
The World's Largest Carbon Sink
The numbers are staggering: the ocean sequesters about 50 times more carbon than the atmosphere and 12 times more than all land plants and soils combined. Around 90% of global CO2 undergoes the marine carbon cycle. Annually, the ocean absorbs about one-third of human-induced emissions, making it our primary natural carbon sink. But how does it work?
The ocean's overturning processes play a crucial role. CO2 dissolved in surface water is transported to the deep ocean through marine currents and mixing processes, accumulating over centuries (physical carbon pump). Simultaneously, CO2 is bound in the formation of marine plant and animal biomass. Many of these organisms, residing in the upper water layers, transport the captured carbon to the depths upon death (biological carbon pump). This process is more responsive to changes as it requires functioning ecosystems. Without it, atmospheric CO2 concentrations would likely be double the current levels.
The Regulatory and Stabilizing Force of Our Climate System under Pressure
The oceans are victims of global warming and, simultaneously, our greatest hope. As the stabilizing force of our climate system, they store heat, influence weather patterns, and act as the planet's primary carbon sink. Protecting the oceans is crucial for our collective future.
Covering 71% of the Earth, constituting 95% of the living biosphere, and holding 97% of the planet's water, oceans are indispensable to life as we know it. Without the intricate network of ocean bodies and current systems, without their productivity, cycles, and interactions with the atmosphere, our current way of life would be unimaginable. However, their ecosystem services are increasingly at risk.
Since 1970, the oceans have absorbed over 90% of the sun's heat. They store 50 times more greenhouse gases than the atmosphere, equivalent to 20-30% of human-induced CO2 since 1980. They are our most critical natural carbon sink, with 93% of global CO2 undergoing the marine carbon cycle. Additionally, they produce 50% of our oxygen, making every other breath we take ocean-originated.
Visible Effects of the Climate Crisis in Oceans
The impacts of the climate crisis are now evident in the oceans. Rising temperatures threaten numerous species and lead to habitat losses. The rise in sea levels is primarily due to heat-induced water expansion. As glaciers and ice caps on land melt, this will further accelerate sea-level rise, resulting in floods and catastrophic events. Another effect is ocean acidification: when CO2 dissolves in water, it forms carbonic acid.
The Intergovernmental Panel on Climate Change (IPCC) raised the alarm in its September 2019 report. The report underscores the urgency of the climate crisis and its ecological and economic ramifications. It also highlights the role oceans play in addressing the crisis and outlines measures for their protection.
Key Findings from the IPCC Report 2019:
Ocean warming has doubled in speed since 1993, intensifying the impacts on storms and rainfall. Arctic ice has decreased by 12.8% each decade. Melting ice sheets could cause a sea-level rise of 40 centimeters to over one meter by 2100. Water temperatures may increase by up to three degrees Celsius, and pH levels could drop to around 7.7. Thawing permafrost threatens to release up to 1,600 gigatons of carbon. Warm surface water disrupts fundamental ocean processes, increasing oxygen-depleted zones globally by 3-8% since 1970. Many marine species' distribution has shifted by several hundred kilometers since the 1950s, negatively impacting fisheries and regional food security. Overall biomass production and habitat quality are decreasing, harmful algal blooms occur earlier and are more pronounced worldwide. Ocean acidification and decreasing oxygen levels affect circulation systems and critical upwelling areas. Coastal vegetation, mangrove belts, or salt marshes have declined by 50% in the 20th century, losing their natural coastal protection function. Seagrass and algae forest stocks have decreased by over 40%. Nearly all warm-water corals are at risk of disappearing with a sea temperature increase of less than two degrees Celsius.
Oceans and Climate Action in Germany
The climate crisis has reached our shores. Cod and herring stocks in the Baltic Sea face collapse. For example, the temperature-dependent spawning behavior of herring and the light-dependent occurrence of phytoplankton have become decoupled. Young herring larvae find insufficient food, as the development of zooplankton follows the phytoplankton, occurring belatedly. The cumulative stress on the seas is visible in the North and Baltic Seas, with the Natura 2000 protected area network not effectively implemented.
In recent years, offshore wind energy has joined the energy transition as a new form of marine use. However, it is not without risks. The case of the Butendiek wind farm west of Sylt illustrates what can happen with poor planning.
The biggest challenge lies in understanding the climate crisis and the biodiversity crisis as a shared and indivisible task. Healthy ecosystems, whether oceans, marshes, or forests, with their natural functions, are among the most potent tools against global warming. Additionally, the expansion of renewable energies must occur within the ecological limits of the systems to avoid jeopardizing natural climate functions. Germany can make a significant contribution to climate crisis mitigation, but discussions on overarching questions about lifestyles, sufficiency, and efficiency are also crucial.
What Must We Do for the Oceans?
Standardized administrative structures for ocean protection and use must align with the threat posed by the climate crisis. A coherent network of well-managed marine protected areas can enhance ocean resilience and secure ecosystem services. Restoration of mangroves, seagrass meadows, and coral reefs must be accelerated. The precautionary principle should be more strongly applied in the use of marine resources, especially in fisheries, considering the climate crisis. The functions of mangroves, marshes, and seagrass meadows as carbon sinks and natural coastal protection must be strengthened. Education through various media and school programs should be promoted from an early age.
