The ocean absorbs 20 to 35 per cent of anthropogenic CO2 emissions, making it the world’s most important carbon sink. A new IASS study takes a closer look at the concept of "blue carbon”, or carbon that is stored in the ocean and coastal ecosystems. While the burning of fossil fuels emits “black” and “brown carbon” that is detrimental to our planet’s health, the world’s forests’ "green carbon” sinks and the global ocean’s blue carbon sinks can to an extent counter these effects by storing atmospheric CO2 in their biomass and underlying sediments. Since the 15th Conference of the Parties of the UN Framework Convention on Climate Change (COP15) in 2009, the potential of blue carbon for climate mitigation has seen continuous incorporation into politics and research. Yet there has been a lag in translating scientific findings into climate policy activities.
How is climate change affecting marine ecosystems?
Humans have been increasing the carbon content of the atmosphere and consequentially the world's oceans for decades. While the average atmospheric temperature increases due to climate change, the world’s oceans are also heating up. Some of the most relevant climate-related pressures to the marine environment include:
- ocean heating
- ocean acidification
- sea level rise
- more frequent and more intense storms and storm surges
In addition to biodiversity loss in the oceans, these changes are also hampering the oceans’ potential to contribute to climate mitigation. The authors of the IASS study discuss the pressures on the marine environment caused by the changing climate and the global dimensions of this problem by focussing specifically on “blue carbon ecosystems”.
Blue carbon can lead to "negative emissions”
CO2 sequestered by blue carbon ecosystems can generate so-called negative emissions that can count as offsets, but the authors argue that this should not lead policymakers to neglect the political and economic steps that will be needed to create a carbon-neutral future. Instead, the restoration and rehabilitation of blue carbon ecosystems as natural carbon sinks should be used as an additional means of achieving significant global emissions reductions.
Globally, coastal blue carbon ecosystems such as mangroves, seagrass beds and salt marshes can currently store over 80 million tonnes of carbon annually. This potential to sequester and store carbon should be included in national and global climate change strategies. However, the authors stress that the following aspects should be taken into account:
- To store carbon indefinitely in their biomass and sediments, blue carbon ecosystems must remain undisturbed. That means that efforts to restore and preserve blue carbon ecosystems to achieve long-term negative emissions will also have to be long-term.
- Current data collection methods are limited. This leads to uncertainties in calculating the regional and global CO2 sequestration potential of blue carbon ecosystems. More accurate estimates of the global extent of blue carbon ecosystems are a prerequisite for assessing their contribution to the global carbon cycle.
- Although exploiting the storage potential of blue carbon ecosystems at the global level should be a top priority for climate policy, local circumstances and trade-offs in ecosystem use must be factored into preservation and restoration measures. Engaging local ecosystem users facilitates long-term planning and management of blue carbon projects and is necessary for their success.
Climate co-benefits of preserving blue carbon ecosystems
In addition to achieving climate-related effects, blue carbon ecosystems hold a wide range of co-benefits for society and the environment that further demonstrate their importance for the climate-ocean-nexus and should be considered in comprehensive policymaking. These include:
- Mangrove forests, seagrass beds (North Sea and Baltic Sea) and salt marshes can contribute to coastal protection against erosion, storms and storm surges. Intact mangrove forests can reduce incoming wave heights by 80 per cent; salt marshes can dampen waves, protecting coastal regions from erosion, storm surges and flooding.
- All blue carbon ecosystems contribute to ocean deacidification by enhancing the marine carbon sink. Some blue carbon ecosystems, such as seagrass beds or kelp forests, can also mitigate the effects of ocean acidification.
- Mangrove forests and seagrass beds can reduce the local consequences of ocean deoxygenation on surrounding ecosystems. Some mangrove species can reduce other nutrients such as nitrites, ammonium nitrogen and reactive phosphorus in coastal waters, while salt marshes can remove heavy metals from seawater.
Beyond their climate-related functions, blue carbon ecosystems can strengthen other areas of global sustainable development and can have socio-cultural benefits for local communities. For example, the protection of biodiversity has positive impacts on the local fishing industry, the tourism industry, and food security in the respective region.
Six recommendations for German marine policy
- Rehabilitate, expand and protect blue carbon ecosystems in German coastal areas at the North and Baltic Sea.
- Strategically integrate climate and marine conservation goals as well as synergetic objectives between marine and biodiversity protection in Germany by incorporating blue carbon ecosystems into integrated coastal management and marine spatial planning.
- Consider European blue carbon ecosystems (seagrass beds and salt marshes) in the EU’s Nationally Determined Contributions (NDCs) and include the blue carbon concept in the German Sustainability Strategy as well as in the federal government’s Climate Action Programme 2030.
- Germany should engage in the UNFCCC and other relevant multilateral processes to support the integration of the blue carbon concept in various policy areas and political processes.
- Support relevant international alliances that work for the recognition of blue carbon in international climate policy processes and by doing so benefit from partners’ knowledge.
- Increasingly promote blue carbon projects in the international arena with national regulatory and funding mechanisms, e.g. via the "International Climate Initiative" (IKI); coordinate the government’s existing funding instruments more comprehensively in terms of the ocean-climate-nexus.
These policy action recommendations were developed together with the Federal Ministry for the Environment, Nature Conservation, Nuclear Safety and Consumer Protection.
Publication (in German):
Röschel, L., Unger, S., Thiele, T., Neumann, B., & Boteler, B. (2022). Klimaschutz durch Meeresnatur: Potentiale und Handlungsoptionen. IASS Studie, 2022. DOI: 10.48481/iass.2022.010