Multi-Century Global and Regional Sea-Level Rise Commitments from Cumulative Greenhouse Gas Emissions in the Coming Decades
- Hakan Sener
- 16 hours ago
- 6 min read
Emissions until 2050 lock in 0.3 m more sea-level rise by 2300 than historical emissions, growing to 0.8 m by 2090—highlighting near-term mitigation's control over multi-century coastal fate.
A 2025 study reveals emissions until 2050 under current climate policies lock in 0.3 m (likely range 0.2-0.5 m) more global mean sea-level rise by 2300 than historical emissions until 2020, growing to 0.8 m (0.5-1.4 m) for emissions until 2090—of which 0.6 m (0.4-1.1 m) could be avoided under very stringent mitigation—with vulnerable Pacific regions facing commitments around 10% higher than the global signal due to enhanced Antarctic contributions.
Published by Alexander Nauels, Zebedee Nicholls, and colleagues from the International Institute for Applied Systems Analysis and multiple international institutions, the research uses a dedicated scenario framework with decadal "drop-to-zero" emissions pathways to isolate sea-level contributions from specific cumulative emission periods. By applying the MAGICC sea-level model calibrated to IPCC AR6 assessments alongside complementary approaches, the study projects global and regional sea-level rise out to 2300 across five SSP-RCP scenarios, revealing that multi-century sea-level rise commitments are strongly controlled by mitigation decisions in coming decades rather than late-century emissions that typically dominate conventional projections.
Key Findings: Near-Term Emissions Lock in Centuries of Sea-Level Rise
Historical Emissions Through 2020 Already Commit to 0.20-0.41 m by 2300
A 2300 global mean sea-level rise commitment of 0.20-0.41 m (66% model or likely range, median 0.29 m) relative to 1995-2014 has already been locked in by historical emissions through 2020. These historically committed lower and upper bounds comprise 33% and 27% of the bounds projected for 2300 under the SSP1-2.6 scenario respectively, dropping to just 9% and 7% under SSP5-8.5, demonstrating that future emissions will dominate long-term sea-level outcomes.
Additional committed sea-level rise from emissions between 2020 and 2030 remains largely independent of emissions pathway choice, but the pathway effect clearly emerges by midcentury. This finding underscores that while some commitment is already inevitable, the magnitude of additional commitment depends critically on near-term mitigation decisions.
2050 Emissions Decisions Create 0.34 m Difference Between Pathways
By 2050, emissions pathway choice produces stark differences in 2300 commitments. Following a 1.5°C-consistent pathway (SSP1-1.9) versus a very high emissions pathway (SSP5-8.5) until 2050 would avoid 0.34 m of median committed sea-level rise by 2300. Current climate policy-like emissions (SSP2-4.5) until 2050 would commit the world to 0.58 m (0.41-0.88 m) by 2300—exceeding the commitment from following SSP1-1.9 through 2090 by more than 0.10 m.
This demonstrates that emissions over just the next 25 years under moderate scenarios create larger multi-century commitments than an additional 40 years under stringent mitigation, highlighting the outsized importance of immediate action versus delayed mitigation.
2090 Commitments Range from 0.44 m to 3.02 m Across Scenarios
Comparing 2300 sea-level rise commitments from cumulative emissions until 2090 reveals steep growth over time under moderate and higher emissions pathways. SSP2-4.5 emissions through 2090 commit to 0.64 m (0.39-1.14 m) more sea-level rise in 2300 compared to the most stringent SSP1-1.9 pathway. Under SSP5-8.5, the 2300 commitment reaches 3.02 m (1.87-4.98 m), with upper bounds of the very likely range approaching 7 m.
However, under SSP1-1.9, the 2300 commitment from 2090 emissions could be limited to just 0.44 m (0.30-0.63 m), underscoring opportunities to avoid substantial long-term commitment through ambitious mitigation. The escalation highlights the rapidly increasing multi-century legacy of continued high emissions.
Carbon Budget Differences Translate to 0.5+ m Sea-Level Differences
Relating 2300 commitments to cumulative net-positive CO₂ emissions reveals that the difference between the 1.5°C (50% likelihood) and 2°C (67% likelihood) carbon budgets translates into more than 0.5 m difference in committed sea-level rise by 2300 for the highest ensemble members. This direct linkage between near-term carbon budgets and multi-century sea-level outcomes provides concrete metrics for evaluating mitigation ambition.
A nonlinear relationship between committed sea-level rise and peak warming emerges, illustrated by quadratic fits showing increasing sensitivity with warming. This feature, only visible on multi-century timescales when ice sheets have time to respond, can be attributed to nonlinear increases in ice mass loss in a warmer world.
Regional Commitments Show 10% Higher Values for Pacific Islands
Regional sea-level rise commitments deviate substantially from global averages due to ocean dynamics, gravitational/rotational/deformational effects from ice-sheet melt, and glacial isostatic adjustment. Vulnerable Pacific regions including Pago Pago (American Samoa) experience commitments around 10% higher than the global signal under SSP2-4.5, driven mainly by larger relative Antarctic contributions.
New York City shows substantially higher than global commitments under both SSP1-1.9 and SSP2-4.5, with positive contributions from glacial isostatic adjustment (the only selected location showing this) and larger Antarctic contributions under SSP2-4.5. Oslo (Norway) demonstrates regional land uplift effects dominating sea-level changes, showing negative sea-level rise under all SSP1-1.9 projections as local vertical uplift exceeds climate-driven commitment signals.
Component Breakdown Reveals Varying Sensitivities to Mitigation
Dissecting emissions by production stage and component reveals that under stringent mitigation (SSP1-1.9), differences between time series of committed 2300 sea-level rise from 2090, 2050, and 2030 emissions remain small, not deviating much from standard scenario projections. This occurs because a larger fraction of sea-level rise is not sensitive to emissions cessation but driven by already-committed contributions from thermal expansion, glaciers, and ice sheets that respond slowly regardless of pathway.
Large areas in the Pacific, South Atlantic, and Indian Ocean experience higher-than-global regional commitments due to above-average contributions from ice-sheet mass loss (particularly Antarctica), glacier mass loss, sterodynamic changes, or combinations of these drivers. These spatial patterns remain consistent across scenarios but with varying magnitudes.
Why This Matters: Irreversible Legacy of Near-Term Decisions
The Nauels et al. study fundamentally reframes sea-level rise discussions by isolating the multi-century consequences of specific emission periods rather than analyzing continuous emission trajectories. This commitment perspective reveals that each additional ton of GHGs emitted in coming decades locks in more multi-century sea-level rise, with implications for Nationally Determined Contributions under the UNFCCC and adaptation planning across timescales from decades to centuries.
The finding that 2050 emissions decisions alone determine whether the world commits to 0.42 m or 0.76 m (median values under SSP1-1.9 versus SSP5-8.5) demonstrates that the next 25 years are disproportionately important for long-term coastal outcomes. Current climate policies committing to 0.58 m by midcentury emissions—exceeding even late-century stringent mitigation commitments—underscores the urgency of immediate action.
For the estimated populations living in coastal cities and vulnerable small island nations, these findings translate to concrete adaptation requirements. The rate of sea-level rise, not just magnitude, determines coastal risk management capacity given different planning, implementation, and intended lifetime timescales ranging from decades for ecosystem-based adaptation to centuries for planned relocation. Multi-century projections capturing larger fractions of the actual sea-level response become essential for this planning.
The updated MAGICC Antarctic component simulating low-likelihood, high-impact contributions captures the IPCC AR6 low-confidence projections under high emissions, with likely ranges for 2300 Antarctic response under SSP5-8.5 (4.70-10.05 m) capturing state-of-the-art Ice Sheet Model Intercomparison Project maximum estimates including ice-shelf collapse of 6.9 m sea-level equivalent. This deliberately highlights rapidly increasing risk from unmitigated emissions while acknowledging deep uncertainties around ice-sheet instabilities.
Regional variations—with Pacific islands facing 10% higher commitments and locations like Oslo showing net sea-level fall due to land uplift—emphasize that detailed assessments of gravitational/deformational effects, glacial isostatic adjustment, and other vertical land motion processes are crucial for determining local climate-driven commitments. Coastal dynamics and river discharge effects requiring high-resolution simulations add further complexity for specific locations.
The tension between exploring long-term changes and limited understanding of sea-level processes on multi-century timescales, particularly after 2100 at regional to local scales, does not prevent exploration of these commitments given their high societal relevance. The severe threat to small islands and vulnerable coasts, plus needs for assessing adaptation requirements and loss and damage, requires multi-century assessments despite uncertainties.
Within stated limitations, this approach provides opportunities to explore sea-level rise committed by cumulative near-term emissions on timescales capturing larger response fractions than the common twenty-first century focus. The results establish direct links between mitigation decisions in coming decades and resulting multi-century responses to better inform both mitigation and adaptation planning, reinforcing how every increment of additional peak warming from cumulative emissions irreversibly increases sea-level rise and emphasizing that stringent mitigation must start today.
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