Can we use the ocean to mitigate climate change? Insights from the IPCC SROCC report

Nathaniel L. Bindoff, Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, TAS, Australia, Phillip Williamson, University of East Anglia, Norwich, United Kingdom, Javier Aristegui, Instituto de Oceanografía y Cambio Global (IOCAG), Universidad de Las Palmas de Gran Canaria, Las Palmas, Spain, William W.L. Cheung, The University of British Columbia, Institute for the Oceans and Fisheries, Vancouver, BC, Canada, Nathalie Hilmi, Consejo Nacional de Investigaciones Científicas y Técnicas, Monaco, Monaco, Robert Hallberg, NOAA/Geophysical Fluid Dynamics Laboratory, Princeton, United States, Nathalie Hilmi, Monaco Scientific Centre, Monaco, Monaco, Nianzhi Jiao, Xiamen University, Xiamen, China, James G. Kairo, Kenya Marine and Fisheries Institute, Kenya, Saiful Karim, Queensland University of Technology, Brisbane, QLD, Australia, Lisa A Levin, Scripps Institution of Oceanography, University of California San Diego, La Jolla, United States, Sean ODonoghue, Climate Change Adaptation Branch City of Durban, Durban, South Africa, Sara Purca Cuicapusa, Instituto del Mar del Peru, Peru, Baruch Rinkevich, Israel Oceanographic and Limnological Research, Haifa, Israel, Toshio Suga, Tohoku University, Graduate School of Science, Sendai, Japan and Alessandro Tagliabue, University of Liverpool, Earth, Ocean and Ecological Sciences, Liverpool, United Kingdom
Abstract:
Ocean interactions with climate are two way: although impacted by warming, they also slow that process, removing greenhouse gases from the atmosphere by both biological and physico-chemical means. The potential for enhancing biologically-driven marine carbon sequestration was assessed by the IPCC Special Report on the Oceans and Cryosphere in the Changing Climate (SROCC). The focus was on coastal ‘blue carbon’ ecosystems, such as mangroves, saltmarshes and seagrass meadows, that occur in more than 150 countries. Large stores of carbon occur in the anoxic sediments associated with such vegetation, resulting from relatively high net accumulation rates on a per unit area basis. Yet at the global scale that contribution would be modest. It would also be difficult to reliably determine, with uncertainties in measuring long-term carbon removal rates and the production of other greenhouse gases. Assessments will also be presented on a range of other ways in which natural ocean processes might be manipulated to increase carbon drawdown, including land-sea integrated eco-engineering (through nutrient management) and ocean fertilisation. We conclude that below-ground carbon storage in vegetated marine habitats can be up to 1000 tC ha, much higher than most terrestrial ecosystems (high confidence). However, due to their limited area, the potential climatic benefits of blue carbon ecosystems can only be a very modest addition to, and not a replacement for, the very rapid reduction of greenhouse gas emissions. The maximum global mitigation benefits of cost-effective coastal wetland restoration is unlikely to be more than 2% of current total emissions from all sources. Preservation and restoration of blue carbon ecosystems is a cost-effective coastal protection tool that can have many co-benefits, including supporting livelihoods, contributing to carbon sequestration, coastal storm protection and the provision of a range of other valuable ecosystem services (high confidence). Additional issues relating to governance and public acceptability arise for those approaches involving the open ocean outside national jurisdictions.
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