Ocean ecosystems have responded and will continue to respond to climate changes of different rates, magnitudes, and durations (virtually certain). Human societies depend on marine ecosystem services, which are sensitive to climate change (high confidence), in particular the provisioning of food (fisheries and aquaculture) and other natural resources; nutrient recycling; regulation of global climate including production of oxygen (O2) and removal of atmospheric carbon dioxide (CO2); protection from extreme weather and climate events; and aesthetic, cultural, and supporting services.
Climate change alters physical, chemical, and biological properties of the ocean (very high confidence). Oceanic drivers include salinity, circulation, temperature, carbon dioxide (CO2), oxygen (O2), nutrients, and light. These drivers shape the physiological performance of individual cells and organisms and ultimately determine ecosystem composition, spatial structure, and functioning. (…)
Rising atmospheric CO2 over the last century and into the future not only causes ocean warming but also changes carbonate chemistry in a process termed ocean acidification (WGI AR5 Sections 3.8.2, 6.4.4). Impacts of ocean acidification range from changes in organismal physiology and behavior to population dynamics (medium to high confidence) and will affect marine ecosystems for centuries if emissions continue (high confidence). Laboratory and field experiments as well as field observations show a wide range of sensitivities and responses within and across organism phyla (high confidence). Most plants and microalgae respond positively to elevated CO2 levels by increasing photosynthesis and growth (high confidence). Within other organism groups, vulnerability decreases with increasing capacity to compensate for elevated internal CO2 concentration and falling pH (low to medium confidence). Among vulnerable groups sustaining fisheries, highly calcified corals, mollusks, and echinoderms are more sensitive than crustaceans (high confidence) and fishes (low confidence). Trans-generational or evolutionary adaptation has been shown in some species, reducing impacts of projected scenarios (low to medium confidence). Limits to adaptive capacity exist but remain largely unexplored. (…)
Pörtner H.-O., Karl D., Boyd P., Cheung W., Lluch-Cota S. E., Nojiri Y., Schmidt D. & Zavialov P., 2014. Ocean systems. 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 A: Global and Sectoral Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, pp. 411-484. Cambridge, United Kingdom and New York, NY, USA: Cambridge University Press. Report chapter.
