Extreme sea level implications of 1.5 °C, 2.0 °C, and 2.5 °C temperature stabilization targets in the 21st and 22nd centuries

Abstract

Sea-level rise (SLR) is magnifying the frequency and severity of extreme sea levels (ESLs) that can cause coastal flooding. The rate and amount of global mean sea-level (GMSL) rise is a function of the trajectory of global mean surface temperature (GMST). Therefore, temperature stabilization targets (e.g. 1.5• C and 2.0 • C of warming above pre-industrial levels, as from the Paris Agreement) have important implications for coastal flood risk. Here, we assess, in a global network of tide gauges, the differences in the expected frequencies of ESLs between scenarios that stabilize GMST warming at 1.5• C, 2.0 • C, and 2.5• C above pre-industrial levels. We employ probabilistic, localized SLR projections and long-term hourly tide gauge records to estimate the expected frequencies of historical and future ESLs for the 21st and 22nd centuries. By 2100, under 1.5• C, 2.0 • C, and 2.5• C GMST stabilization, the median GMSL is projected to rise 48 cm (90% probability of 28-82 cm), 56 cm (28-96 cm), and 58 cm (37-93 cm), respectively. As an independent comparison, a semi-empirical sea level model calibrated to temperature and GMSL over the past two millennia estimates median GMSL rise within 7-8 cm of these projections. By 2150, relative to the 2.0• C scenario and based on median sea level projections, GMST stabilization of 1.5• C spares the inundation of lands currently home to about 5 million people, including 60 000 individuals currently residing in Small Island Developing States. We quantify projected changes to the expected frequency of historical 10-, 100-, and 500-year ESL events using frequency amplification factors that incorporate uncertainty in both local SLR and historical return periods of ESLs. By 2150, relative to a 2.0• C scenario, the reduction in the frequency amplification of the historical 100 year ESL event arising from a 1.5• C GMST stabilization is greatest in the eastern United States, with ESL event frequency amplification being reduced by about half at most tide gauges. In general, smaller reductions are projected for Small Island Developing States.

Uncertainty in Sea Level Rise Projections Due to the Dependence Between Contributors

“…With 5th to 95th percentiles between brackets. Rasmussen et al () found a similar result with a r 2 of 0.10, which is equivalent to a Pearson correlation coefficient of 0.3. This shows that the simple assumption of a correlation coefficient of 1 made in Church et al () can be refined.…”

Predicted Chance That Global Warming Will Temporarily Exceed 1.5 °C

“…We stress that a temporary excursions over 1.5 °C above preindustrial conditions would not necessarily constitute an exceedance of the Paris Agreement, which has been interpreted to refer to human‐induced climate change over periods of at 30 years (Rogelj et al, ). Indeed, complying with the Paris Agreement is still achievable (Rogelj et al, ) and important, given the impact of further warming on Arctic Sea Ice (Jahn, ; Niederdrenk & Notz, ; Sigmond et al, ), Greenland, and West Antarctic ice sheets and sea level rise (Rasmussen et al, ), regional climate (Jacob et al, ; M. A. Taylor et al, ), and extremes (Dosio & Fischer, ; Li et al, ). The first temporary excursions above 1.5 °C, if they occur, would not necessarily lead to many of these effects but they would be an important indication of the proximity to the Paris threshold and could generate interest from the media and general public.…”

A Statistical Model for Frequency of Coastal Flooding in Honolulu, Hawaii, During the 21st Century

“…Counts of sea level exceedances per year above a threshold are often assumed to follow a Poisson distribution (e.g., Cid et al, ; Rasmussen et al, ). Maximum likelihood estimates of the Poisson probability mass function that best describe the histograms from the Honolulu threshold experiment show some similarity with the histogram at low values of Δ 99 (Figure b).…”