Evolution of 21st Century Sea Level Rise Projections

Abstract

The modern era of scientific global-mean sea level rise (SLR) projections began in the early 1980s. In subsequent decades, understanding of driving processes has improved, and new methodologies have been developed. Nonetheless, despite more than 70 studies, future SLR remains deeply uncertain. To facilitate understanding of the historical development of SLR projections and contextualize current projections, we have compiled a comprehensive database of 21st century global SLR projections. Although central estimates of 21st century global-mean SLR have been relatively consistent, the range of projected SLR has varied greatly over time. Among studies providing multiple estimates, the range of upper projections shrank from 1.3-1.8 m during the 1980s to 0.6-0.9 m in 2007, before expanding again to 0.5-2.5 m since 2013. Upper projections of SLR from individual studies are generally higher than upper projections from the Intergovernmental Panel on Climate Change, potentially due to differing percentile bounds or a predisposition of consensus-based approaches toward relatively conservative outcomes.Plain Language Summary In spite of more than 35 years of research, and over 70 individual studies, the upper bound of future global-mean sea level rise (SLR) remains deeply uncertain. In an effort to improve understanding of the history of the science behind projected SLR, we present and analyze the first comprehensive database of 21st century global-mean SLR projections. Results show a reduction in the range of SLR projections from the first studies through the mid-2000s that has since reversed. In addition, results from this work indicate a tendency for Intergovernmental Panel on Climate Change reports to err on the side of least drama-a conservative bias that could potentially impede risk management.

Framework for High‐End Estimates of Sea Level Rise for Stakeholder Applications

“…Alternative futures described by probabilistic projection and conditioned to RCP scenarios (e.g., Kopp et al, 2014;Jackson & Jevrejeva, 2016;De Winter et al, 2017;Kopp et al, 2014;Garner et al, 2018) High-end scenarios provided in a probabilistic form, and assuming high greenhouse gas emissions and ice contributions (Jackson & Jevrejeva, 2016;Le Bars et al, 2017) See above: probabilistic projections provide some basis to estimate the most likely scenarios, but there is limited confidence in higher quantiles Le Cozannet, Nicholls, et al, 2017).…”

“…A dominant cause of future long-term sea level rise is anthropogenic CO 2 emissions (Church et al, 2013), and the response of individual climate system components to the associated temperature increase, notably the thermal expansion of ocean water and mass loss from glaciers, and ice sheets, which add mass and volume to the ocean. An overview of sea level projection available during for 21st century is presented by Garner et al (2018). Recently, the fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC) provided a likely range of future sea level rise under various climate change scenarios (Church et al, 2013;Slangen et al, 2014), thereby accounting for expert judgment on the interpretation of the range of simulated model outputs.…”

“…Recently, the fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC) provided a likely range of future sea level rise under various climate change scenarios (Church et al, 2013;Slangen et al, 2014), thereby accounting for expert judgment on the interpretation of the range of simulated model outputs. An overview of sea level projection available during for 21st century is presented by Garner et al (2018).…”

Adaptation to uncertain sea-level rise; how uncertainty in Antarctic mass-loss impacts the coastal adaptation strategy of the Netherlands

“…Similar to other coastal zones, the Dutch Delta Program relies on SLR-assessments from the Intergovernmental Panel on Climate Change (IPCC), which are further tailored to local scenarios [24]. Over the past decades, SLR scenarios from the IPCC were fairly stable, envisaging a global mean SLR up to 1.1 m between 1990 and 2100 [25,26] with a likely range (representing at least 66% probability) of 0.26-0.98 m in the IPCC Fifth Assessment Report [27]. In the recent Special Report on Oceans and Cryosphere in a changing Climate (SROCC) [28], the upper bound of the likely range was adjusted upwards to 1.1 m in 2100 for a high emission scenario (Representative Concentration Pathway (RCP) 8.5).…”

“…Despite the growth of scientific studies about Antarctica, its contribution to future rate of SLR is still highly uncertain and undergoing a strong scientific debate [30]. In fact, the uncertainty in projected SLR increased recently [26,53]. In decision making literature this is referred to as 'deep uncertainty' [10], which occurs when experts do not have sufficient knowledge or when parties to a decision cannot agree upon the system processes and futures.…”