The Ocean plays a central role in Earth’s climate and has absorbed 93% of the extra energy from the enhanced greenhouse effect and approximately 30% of anthropogenic carbon dioxide (CO2) from the atmosphere. Regional responses are addressed here by dividing the Ocean into seven sub-regions: High-Latitude Spring Bloom Systems (HLSBS), Eastern Boundary Upwelling Ecosystems (EBUE), Coastal Boundary Systems (CBS), Equatorial Upwelling Systems (EUS), Subtropical Gyres (STG), Semi-Enclosed Seas (SES), and the Deep Sea (DS; >1000 m). An eighth region, Polar Seas, is dealt with by Chapter 28. (…)
Uptake of CO2 has decreased ocean pH (approximately 0.1 unit over 100 years), fundamentally changing ocean carbonate chemistry in all ocean sub-regions, particularly at high latitudes (high confidence). The current rate of ocean acidification is unprecedented within the last 65 Ma (high confidence), if not the last 300 Ma (medium confidence). Warming temperatures, and declining pH and carbonate ion concentrations, represent risks to the productivity of fisheries and aquaculture, and the security of regional livelihoods given the direct and indirect effects of these variables on physiological processes (e.g., skeleton formation, gas exchange, reproduction, growth, and neural function) and ecosystem processes (e.g., primary productivity, reef building and erosion) (high confidence). (…)
Rapid changes in physical and chemical conditions within ocean sub-regions have already affected the distribution and abundance of marine organisms and ecosystems. Responses of species and ecosystems to climate change have been observed from every ocean subregion (high confidence). Marine organisms are moving to higher latitudes, consistent with warming trends (high confidence), with fish and zooplankton migrating at the fastest rates, particularly in HLSBS regions. Changes to sea temperature have also altered the phenology, or timing of key life-history events such as plankton blooms, and migratory patterns and spawning in fish and invertebrates, over recent decades (medium confidence). There is medium to high agreement that these changes pose significant uncertainties and risks to fisheries, aquaculture, and other coastal activities. Ocean acidification maybe driving similar changes (low confidence), although there is limited evidence and low
agreement at present. The associated risks will intensify as ocean warming and acidification continue.
Regional risks and vulnerabilities to ocean warming and acidification can be compounded by non-climate related stressors such as pollution, nutrient runoff from land, and over-exploitation of marine resources, as well as natural climate variability (high confidence). These influences confound the detection and attribution of the impacts of climate change and ocean acidification on ecosystems yet may also represent opportunities for reducing risks through management strategies aimed at reducing their influence, especially in CBS, SES, and HLSBS. (…)
Hoegh-Guldberg O., Cai R., Brewer P., Fabry V., Hilmi K., Jung S., Poloczanska E. & Sundby S., 2014. The ocean. In: Field C. B., Barros V. R., Dokken D. J., Mach K. J., Mastrandrea M. D., Bilir T. E., Chatterjee M., Ebi K. L., Estrada Y. O., Genova R. C., Girma B., Kissel E. S., Levy A. N., MacCracken S., Mastrandrea P. R. & White L. L. (Eds.), Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part B: Regional Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, pp. 1655-1731. Cambridge, United Kingdom and New York, NY, USA, Cambridge: Cambridge University Press. Report chapter.
