Editing IPCC:AR6/SROCC/Chapter-5 (section)

== 5.7 Key Uncertainties and Gaps ==

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This chapter was designed around three guiding questions (Section 5.1). These guiding questions mean that the report covers both regional and global scales of the ocean and many aspects of human systems, including governance and institutions, and adaptation pathways for dependent communities. This assessment is new linking together a broad and complex set of ocean disciplines and therefore also provides a unique perspective on key uncertainties and gaps in these systems. These gaps limit the extent of the assessments that were possible in this report. Notable outstanding uncertainties and gaps from this assessment include the following:

'''Physical and biogeochemical processes:''' While the Earth system is better monitored and the relevant data are more accessible than the other areas of assessment there is considerable room to improve these capabilities. For example, gaps remain in predictive modelling of climate change in coastal areas, deep ocean temperature and salinity measurements for sea level and closure of the energy budget, and oxygen and carbon measurements dense enough to measure deoxygenation of the world ocean and track the mechanisms driving the ocean carbon cycle. Our capacity to understand and model net primary productivity and the rates of carbon burial in coastal sediments are also significant weaknesses. Projections of future changes in the Earth system depend on the use of ESMs, in which there are uncertainties arising from physical or ecological processes that are either omitted or incompletely understood. Most ESMs still rely on relatively simple representations of ocean biogeochemical cycling and the linkages to ocean ecosystem structure and function (Section 5.2.3). Other examples of under-assessed biogeochemical process in the ocean that may have implications for the Earth system under climate change include the fate of methane in the deep ocean (Section 5.2.4). Open ocean primary productivity and its projections requires critical corroborating measurements and improved understanding of its drivers to project changes in ocean productivity with higher confidence (Sections 5.2.2 and 5.2.3).

'''Biological processes and monitoring:''' There are a number of marine environments (e.g., on the deep sea floor) and ecosystem components (e.g., viruses and protists) where insufficient scientific understanding limits the assessments of risks to ''low confidence or no assessment.'' Examples of gaps include the narrow range of climate and non-climatic hazards and their interactions in simulation models, the linkages between single organisms to communities of organisms, knowledge of climate feedbacks in biological systems (Section 5.3.4, Section 5.2.4), and the capacity and limits of biological adaptation for many ecosystems (Section 5.2.2, 5.2.3, 5.2.4, 5.3). Increasing observational capacity can help provide the data to improve understanding and modelling of these important biophysical responses to climate change.

'''Variance in human systems and effectiveness of responses:''' The wide range of contributing factors (physical, social and economic) that interact with localised climate projections make projecting site-specific costs of impacts and benefits of adaptation difficult. There were few examples in the literature evaluating implemented adaptation actions, and there was ''low confidence'' in their reliability and provenance, thus largely precluding any assessments of their cost effectiveness. This lack of evidence on costs and benefits particularly affected assessments in Section 5.4 and 5.5. Adaptation responses to climate change have been undertaken by communities, industry and governments. However, their effectiveness for mitigating the risks of climate change (e.g., different types of adaptation response on the coasts, Section 5.5.2) is largely unassessed here, and consequently precludes a global understanding of the capacity in the world to address the risks of climate change in coastal seas, open ocean and the deep sea. A partial solution would be establishing an appropriate ocean and coasts database, including costs-benefits, for these types of studies .

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