Time of Emergence of Key Climate Change Variables and Exposure to Climate Hazards in the Ocean

Javier Aristegui, Instituto de Oceanografía y Cambio Global (IOCAG), Universidad de Las Palmas de Gran Canaria, Las Palmas, Spain, Alessandro Tagliabue, University of Liverpool, Earth, Ocean and Ecological Sciences, Liverpool, United Kingdom, Nathaniel L. Bindoff, University of Tasmania, Institute for Marine and Antarctic Studies, Hobart, TAS, Australia, 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 Phillip Williamson, University of East Anglia, Norwich, United Kingdom
Abstract:
Time of emergence (ToE) is defined as the time at which the signal of climate change in a given variable emerges from a measure of the background variability or noise. ToE of variables related to climatic hazards to marine organisms and ecosystems such as sea surface temperature (SST), pH, carbonate ion concentrations, aragonite and calcite saturation states, nutrient levels and net primary productivity (NPP) was assessed by the IPCC Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC). Earth System Models show that there is an ordered emergence of these climate variables, with pH emerging rapidly across the entire open ocean, followed by SST, interior oxygen, upper ocean nutrient levels and finally NPP, under both RCP2.6 and RCP8.5 relative to the 1861-1900 reference period. Anthropogenic signals remain detectable for over large parts of the ocean even for the RCP2.6 scenario for pH and SST, but are likely to be lower for nutrients and NPP in the 21stcentury. Although signals of anthropogenic influences have already emerged from internal variability in the late 20th century for global and basin-scale averaged ocean climate variables (from IPCC AR5), their ToE and level of confidence vary greatly at local scales and in coastal seas. From an observational standpoint, time series of around a decade are sufficient to detect a trend in pH or SST, whereas datasets spanning 30 years or longer are typically needed for detection of emergence at local scales for oxygen, nitrate and NPP. The rapid emergence of hazards at the local scale in the near-term (already past or in this decade) such as warming and ocean acidification, and the resulting impacts on some of the more sensitive or less adaptive biodiversity and ecosystem services, may pose challenges for international and regional policies, as they often require multiple decades to designate and implement. In contrast, scope for adaptation for national and local ocean governance can be more responsive to rapid changes. This highlights the opportunities for multi-level adaptation that allows for reducing climate risks that are expected to emergence of stressors and impacts at different time frame.

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