# Evolving understanding of Antarctic ice-sheet physics and ambiguity in probabilistic sea-level projections

## TL;DR

This paper integrates physical Antarctic ice-sheet models into probabilistic sea-level projections, revealing significant potential increases in sea-level rise and population impact under high emissions, emphasizing the importance of adaptive strategies.

## Contribution

It introduces a physical model-based approach to sea-level projections, improving sensitivity analysis and highlighting uncertainties in future ice-sheet contributions.

## Key findings

- Median GMSL rise under RCP 8.5 increases from 79 to 146 cm.
- Projected land inundation by 2100 could affect 197 million more people.
- Future projections show over 10 m GMSL rise by 2300 under high emissions.

## Abstract

Mechanisms such as ice-shelf hydrofracturing and ice-cliff collapse may rapidly increase discharge from marine-based ice sheets. Here, we link a probabilistic framework for sea-level projections to a small ensemble of Antarctic ice-sheet (AIS) simulations incorporating these physical processes to explore their influence on global-mean sea-level (GMSL) and relative sea-level (RSL). We compare the new projections to past results using expert assessment and structured expert elicitation about AIS changes. Under high greenhouse gas emissions (Representative Concentration Pathway [RCP] 8.5), median projected 21st century GMSL rise increases from 79 to 146 cm. Without protective measures, revised median RSL projections would by 2100 submerge land currently home to 153 million people, an increase of 44 million. The use of a physical model, rather than simple parameterizations assuming constant acceleration of ice loss, increases forcing sensitivity: overlap between the central 90% of simulations for 2100 for RCP 8.5 (93-243 cm) and RCP 2.6 (26-98 cm) is minimal. By 2300, the gap between median GMSL estimates for RCP 8.5 and RCP 2.6 reaches >10 m, with median RSL projections for RCP 8.5 jeopardizing land now occupied by 950 million people (vs. 167 million for RCP 2.6). The minimal correlation between the contribution of AIS to GMSL by 2050 and that in 2100 and beyond implies current sea-level observations cannot exclude future extreme outcomes. The sensitivity of post-2050 projections to deeply uncertain physics highlights the need for robust decision and adaptive management frameworks.