| Summary: | © 2017 Dr. Alexander Nauels Global sea levels increased by around 0.2 m over the 20th century and will continue to rise during the 21st century and far beyond. This has profound implications for coastal populations, infrastructure and ecosystems around the globe. Efforts to assess future impacts on low-lying coastal areas need to be based on robust projections capturing the latest physical understanding of sea level drivers. This PhD research project provides an efficient and robust modelling tool that more consistently links the future sea level response to plausible emission scenarios and allows for extensive uncertainty assessments of long-term sea level projections until 2300. The new MAGICC sea level model is consistent with the Fifth Assessment Report (AR5) of the IPCC. It has been extended to also account for more recent research suggesting additional Antarctic discharge dynamics. In the IPCC AR5 consistent setup, global mean sea levels in 2100 are projected to rise between 0.4 and 0.6 m (66% range) under RCP 2.6 and between 0.7 and 1.0 m under RCP8.5, relative to 1986-2005. Global Mean Sea Level Rise (GMSLR) projections for the year 2300 yield median responses of around 1.1 m for RCP 2.6, 1.8 m for RCP 4.5, 2.4 m for RCP 6.0, and 4.8 m for RCP 8.5. If additional Antarctic rapid dynamics are included, we project 2300 median GMSLR of around 1.0 m under RCP 2.6, 3.3 m under RCP 4.5, 5.3 m under RCP 6.0, and 13.4 m under RCP 8.5. For the new Shared Socioeconomic Pathways (SSPs) without dedicated climate mitigation, 2100 GMSLR is projected to range between 1.0 and 1.9 m (66% range) for a 21st century storyline of high fossil-fuel use and energy demand. SSP pathways staying below 2 degC of warming relative to pre-industrial levels with a likely chance yield 2100 median GMSLR between 0.3 and 0.8 m. 2100 median SSP GMSLR could be limited to around 0.5 m if 2050 cumulative CO2 emissions since pre-industrial stayed below 850 GtC and the global coal phase-out was nearly completed by that time. The analysis of GMSLR under Paris Agreement climate targets clearly points to the need for early and stringent CO2 emission reductions between 2020 and 2035 for limiting 2300 GMSLR to around 1 m relative to 1986-2005. The Antarctic ice sheet represents the most uncertain but also potentially largest future sea level contribution, followed by the Greenland ice sheet and ocean thermal expansion. Due to its great scenario flexibility and robust 2300 projection capability, the MAGICC sea level model would be well suited to feed into regional sea level rise and coastal impact assessments.
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