The Transient Sea Level Response to External Forcing in CMIP6 Models

Area of Science:

• Climate science
• Glaciology
• Oceanography

Background:

• Earth is warming, leading to sea level rise (SLR) from melting land ice and thermal expansion of oceans.
• The rate of SLR is linked to warming intensity, but future projections remain uncertain.
• Quantifying transient sea level sensitivity is crucial for understanding climate change impacts.

Purpose of the Study:

• To quantify the transient sea level sensitivity of the sea level budget using models and observational data.
• To compare the sensitivity of different contributors to SLR across different time periods.
• To identify potential biases in model simulations of SLR.

Main Methods:

• Analysis of sea level budget components, including glaciers and ice caps (GIC), Greenland Ice Sheet, Antarctic Ice Sheet (AIS), and steric expansion.
• Comparison of model-derived sensitivities with historical data.
• Calculation of transient sea level sensitivity (mm/yr/K) for each component.

Main Results:

• GIC show higher sensitivity pre-2050 (2.8 ± 0.4 mm/yr/K) than later (0.7 ± 0.1 mm/yr/K) due to their rapid response time.
• Model sensitivities for steric expansion (1.5 ± 0.2 mm/yr/K) and Greenland Ice Sheet (0.8 ± 0.2 mm/yr/K) align with historical estimates.
• AIS models underestimate historical SLR sensitivity (-0.0 ± 0.3 mm/yr/K vs. 0.4 ± 0.2 mm/yr/K), contributing to a low bias in global SLR projections.

Conclusions:

• Sea level rise sensitivity varies significantly among contributing factors and over time.
• Models show a low bias in Antarctic Ice Sheet contribution to SLR.
• Mitigating SLR requires substantial global cooling, as the balance temperature is near pre-industrial levels.