Using Global Ocean Models to Project Sea Level Rise Robert Hallberg NOAA / GFDL.

Using Global Ocean Modelsto Project Sea Level Rise

Robert Hallberg

NOAA / GFDL

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iseSources of uncertainty in 2100 global mean sea level projections:

Forcing scenario (~20 cm range at 2100 for GFDL-CM2.1)Ocean heat storage (steric rise) (13 to 32 cm in IPCC AR4)Land ice (except ice sheets) (4 to 19 cm in IPCC AR4)Ice sheet surface mass balance (-10 to 4 cm in IPCC AR4)Dams & land water ±3 cm/century? (Lettenmaier & Milly, Nature Geo. 2009)

Antarctic & Greenland Ice sheet dynamics changes – ? Plausible range 20 to 110 cm by 2100 (Pfeffer et al., Science 2008)

Projected Global Mean Sea Level Rise

Reservoir sizes in Sea Level Rise equivalent: Mountain glaciers & ice caps – 0.3 m Greenland Ice Sheet – 7.3 m West Antarctic Ice Sheet (marine) – 5 m East Antarctic Ice Sheet (land) – 51.6 m(Uniform warming of ocean ~0.5 m °C-1)

“Observed” and ModeledDecadal Mean Sea Surface Height

10-Year average inferred from observations, 1992-2002

A GFDL coupled climate model with 1990 atmospheric CO2

Global SLR from Ocean Thermal Expansion in IPCC 4th Assessment Report (AR4) Models (2007)

Note: Models have no ice-sheet dynamics!

21st Century Ocean Dynamics SLR Anomalies from the Global Mean in 12 IPCC AR4 Coupled Models

Yin, Griffies & Stouffer, J. Climate 2010

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Hatching = Signal exceeds 1.5 standard deviations of ensemble

Sea Level Trends in GFDL’s CM2.1 Coupled Model

Yin, Griffies & Stouffer, J. Climate 2010

Note: CM2.1 has no ice-sheet dynamics!

Sea Level Trends in GFDL’s CM2.1 Coupled Model

Yin, Griffies & Stouffer, J. Climate 2010

Note: CM2.1 has no ice-sheet dynamics!

21st Century Thermosteric and HalostericSea Level Rise Anomalies in GFDL’s CM2.1

Yin, Griffies & Stouffer, J. Climate 2010

Local Anomalies of SLR due toOcean Temperature Changes

Local Anomalies of SLR due toOcean Salinity Changes

1° Coupled ModelJune SSH

Annual Mean SSHInferred from Obs.

1/8° Global Ocean ModelJune SSH

Ocean Influence on Jakobshavn Glacier, Greenland

Holland et al., 2008, Nature Geoscience.

50 km

Satellite Image from NASA

Regional Sea Level Change from Geoid Changes• Gravitational attraction by the Ocean, Ice-sheets, and Soil-moisture mass distributions help shape

the Earth’s geoid (resting sea-level).

• Geoid changes will be an important part of regional sea level rise.

<0 1 1.40.2 1.20.4 0.6 0.8

Sea-level rise per meter equivalent Greenland melt (m)

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Kopp et al., 2009 (sub.)

What is needed to model ice-sheet dynamics contributions to global mean sea level rise?

Bamber et al., Science 2000; C. Rapley, British Antarctic Survey

1. Ice sheet dynamics model, including the ability to simulate the rapidly flowing ice streams.

2. Ice shelf model, including calving of ice-bergs and collapse.

3. Model of the ocean circulation in the ice-shelf cavity.

4. Parameterizations or resolution of the eddy- and tidal- delivery of warm ocean water to the ice shelf cavity.

Ocean-weather heat transport

Ice Shelf

Cold-fresh

Warm-salty

melts

Higher resolution coupled models are coming, but …Higher resolutions are much more expensive to run: 1/8° ≈ 512x 1°

New algorithms are needed for the simulations to be acceptable for climate runs.

Spurious diapycnal mixing in coupled climate models?