Abstract
Sea-level rise (SLR) is a long-lasting consequence of climate change
because global anthropogenic warming takes centuries to millennia to
equilibrate. SLR projections based on climate models support policy
analysis, risk assessment and adaptation planning today, despite their
large uncertainties. The central range of the SLR distribution is
estimated by process-based models. However, risk-averse practitioners
often require information about plausible future conditions that lie in
the tails of the SLR distribution, which are poorly defined by existing
models. Here, a community effort combining scientist and practitioners,
builds on a framework of discussing physical evidence to quantify
high-end global SLR for practice. The approach is complementary to the
IPCC AR6 report and provides further physically plausible high-end
scenarios. High-end estimates for the different SLR components are
developed for two climate scenarios at two timescales. For global
warming of +2 ˚C in 2100 (SSP1-2.6) relative to pre-industrial values
our high-end global SLR estimates are up to 0.9 m in 2100 and 2.5 m in
2300. Similarly, for +5 ˚C (SSP5-8.5) we estimate up to 1.6 m in 2100
and up to 10.4 m in 2300. The large and growing differences between the
scenarios beyond 2100 emphasize the long-term benefits of mitigation.
However, even a modest 2 ˚C warming may cause multi-meter SLR on
centennial time scales with profound consequences for coastal areas.
Earlier high-end assessments focused on instability mechanisms in
Antarctica, while we emphasize the timing of ice-shelf collapse around
Antarctica, which is highly uncertain due to low understanding of the
driving processes.