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Presentation Mode : All
Conference Day : 06/08/2021
Time Slot : AM2 11:00 - 13:00
Sections : OS - Ocean Sciences










Ocean Sciences | Fri-06 Aug




OS15-A003
Global Mean Thermosteric Sea Level Projections by 2100 in CMIP6 Climate Models

Svetlana JEVREJEVA1#+, Hindumathi PALANISAMY1, Luke JACKSON2
1Centre for Climate Research Singapore, Singapore, 2Department of Geography, University of Durham, United Kingdom


Most of the excess energy stored in the climate system is taken up by the oceans leading to thermal expansion and sea level rise. Future sea level projections allow decision-makers to assess coastal risk, develop climate resilient communities and plan vital infrastructure in low- elevation coastal zones. Confidence in these projections depends on the ability of climate models to simulate the various components of future sea level rise. In this study we estimate the contribution from thermal expansion to sea level rise using the simulations of global mean thermosteric sea level from 15 available models in the Coupled Model Intercomparison Project Phase (CMIP) 6. We calculate a global mean thermosteric sea level rise of 18.8 cm [12.8 - 23.6 cm, 90% range] and 26.8 cm [18.6 - 34.6 cm, 90% range] for the period 2081–2100, relative to 1995-2014 for SSP245 and SSP585 scenarios respectively. In a comparison with a 20 model ensemble from CMIP5, the CMIP6 ensemble mean of future global mean thermosteric sea level rise (2014-2100) is higher for both scenarios and shows a larger variance. By contrast, for the period 1901-1990, global mean thermosteric sea level from CMIP6 has half the variance of that from CMIP5. Over the period 1940-2005, the rate of CMIP6 ensemble mean of global mean thermosteric sea level rise is 0.2 ± 0.1 mm yr-1, which is less than half of the observed rate (0.5 ± 0.02 mm yr-1).  We further discuss the difference in global mean thermosteric sea level sensitivity to the changes in global surface temperature over the historical and future periods.

OS15-A008 | Invited
Development of Downscaled Ocean Datasets from CMIP5 Projections and Applications to Coastal and Sea-level Studies in Japan

Shiro NISHIKAWA1#+, Kei SAKAMOTO2, Goro YAMANAKA2, Tsuyoshi WAKAMATSU3, Yoichi ISHIKAWA1
1Japan Agency for Marine-Earth Science and Technology, Japan, 2Japan Meteorological Agency, Japan, 3Nansen Environmental and Remote Sensing Center, Norway


In this study, we developed two high-resolution future ocean regional projection datasets for coastal applications in Japan, in which we made use of dynamical downscaling via regional ocean models with atmospheric forcing from several climate models participating in Coupled Model Intercomparison Project Phase 5 (CMIP5) under historical, representative concentration pathways (RCP) 2.6, and RCP8.5 scenarios. The first dataset is an eddy-resolving 10-km resolution product covering the North Pacific Ocean area and ranging continuously from 1981 to 2100, in which the Kuroshio current and mesoscale structures were reasonably resolved. The second dataset is a 2-km resolution product covering the regional domain surrounding Japan and comprising several 15-year time slices, in which the coastal geometry and current structure were resolved even more realistically. An important feature of these datasets is the availability of reference datasets based on atmospheric and oceanic reanalysis data for cross-validation during the historical run period. Utilizing the high-resolution property of the downscaled data, possible future impact analyses regarding coastal phenomena such as coastal sea level variability are demonstrated.

OS15-A004
Projection of Trend and Variability of Regional Sea Level Rise Based on Miroc6 Ensemble

Miho MIYAUCHI1#+, Nobuhito MORI1, Tomoya SHIMURA1, Hiroaki TATEBE2
1Kyoto University, Japan, 2Japan Agency for Marine-Earth Science and Technology, Japan


This study examines long-term assessment for sea level rise based on SROCC and MIROC6 ensemble experiments for IPCC AR6. We analyze trends, seasonal to decadal variabilities of sea surface height (SSH) for modeled SSH and observed long-term SSH in the regional scale. The natural variability of SSH has a variety of spatial pattern and time scale, and is significant in comparison with the long term trend of low emission scenario such as RCP2.6/SSP1-26. The probabilistic characteristics of regional SSH are also discussed both natural variability and GCM based variability which correspond to epistemic and aleatory uncertainty.

OS15-A016
Developing Sea Level Projections for Coastal Climate Services in Asia, Oceania and the Caribbean

Jennifer WEEKS#+, Benjamin HARRISON, Joseph DARON
Met Office, United Kingdom


Sea level rise presents an acute threat to the natural and human systems of low-lying coastal areas and small island states. Future exposure and vulnerability of these coastal systems will be determined by the interaction of high-frequency local climate variability with long-term trends in sea level rise, coastal urbanization, and economic development. Consideration of the interaction of these multiscale processes in coastal planning presents a major challenge, since until recently, coastal risk assessments have been restricted to using global sea level projections, alongside trends from short-duration (and often unreliable) tide gauge records. Here, we present Met Office work aiming to address the gaps in the provision and use of local sea level rise projections through coastal climate services in Asia, Oceania, and the Caribbean. We discuss the new regional sea level projections that were produced for these projects using the methodology developed for the national UK climate projections in 2018. We describe how these projections can be used to communicate information on the physical drivers of sea level change and the sources of uncertainty in sea level projections for these contrasting regions. We also compare how stakeholder engagement and capacity development has varied across the different projects, highlighting where changes to the common science outputs have been required and where new research will be required to address limitations.    

OS15-A012
High-end Sea-level Rise Projection

Roderik VAN DE WAL1#+, Robert NICHOLLS2
1Department of Physical Geography, Netherlands, 2University of East Anglia, United Kingdom


Sea-level change is a key aspect of climate change, because human interference in the system leads to a gradual warming and expansion of ocean water, melting of glaciers and ice sheets and changes in landwater storage. Process-based models can provide an estimate of the central distribution of change, including mean change. However, many users of sea-level rise information also need information on the tails of the distribution. Here, we build on a framework of building blocks leading to storylines generating an estimate of high-end sea-level change. It aims to provide practioners with actionable information on low likelihood, high consequence cases. We focus on two climate scenarios at two time scales and describe the storylines shaping the high-end estimates of the different components contributing to sea-level rise. For a +2K scenario we estimate 0.8 m global mean sea level in 2100 and 3.4 m in 2300. For a +4K scenario we estimate 1.7 m in 2100 and 10 m in 2300. These large differences emphasize the long time scales of the problem and the long-term benefits of mitigation. However, even a modest warming may lead to a large sea-level rise on long time scales, reflecting the large uncertainty in the Antarctic sea-level contribution. Hence adaptation implications must be considered.