Title slide

Volcanic eruptions: their impact on sea level and oceanic heat content

John A. Church1,2*, Neil J. White1,2 and Julie M. Arblaster3,4

1 CSIRO Marine Research, GPO Box 1538, Hobart Tasmania. 7001. Australia. 2 ACE CRC, Hobart, Tasmania, Australia

3 National Center for Atmospheric Research, Boulder, Colorado, USA4 Bureau of Meteorology Research Centre, Melbourne, Victoria, Australia

Mt Pinatubo eruption in the Philippines, June 15, 1991.

Gases and solids injected 20 km into the stratosphere.

Reconstructed global average sea level for the period 1950 to 2000

Agung 1963

El Chichon 1982

Mt Pinatubo 1991

Radiative forcing of climate

From Ramswamy et al., 2001, IPCC TAR

Peaks of -5 W m-2 following major explosive volcanic eruptions

From Ramswamy et al., 2001, IPCC TAR

Different stratospheric loading models

PCM 20thC ensembles: 1890-1999

V volcanicS solarG ghgSu sulfatesOz ozoneSOz solar+ozoneVS volcanic+solarVSOz volcanic+solar+ozoneGS ghg+sulfatesGOz ghg+ozoneGSuOz ghg+sulfates+ozoneSGSuOz solar+ghg+sulfates+ozoneVSGSuOz volcanic+solar+ghg+sulfates+ozone (ALL)

4 members each with the following forcings:

DOE/NCAR Parallel Climate ModelAtmosphere CCM3 T42 18L ~ 2.8 degree

Land LSM

Ocean POP 32L ~2/3 degree

Sea-ice Dynamic and thermodynamic

Observed concentrations and loadings used to force the model

Simulated GMSL with/without volcanic forcing 1890-2000

Differences in GMSL between simulations with/without volcanic

forcing1890-2000

Volcanic forcing results in a rapid fall in GMSL of ~5 mm

Differences in global ocean heat content between simulations with/without

volcanic forcing1890-2000

Volcanic forcing results in a fall in global average heat content of ~3 x 1022 J

Much of the heat content changes in the upper 200 m but some deeper signals

Can we detect the signal in observations?

• In models can– Isolate forcing– Use ensembles to average variability

• Observations – many signals – natural variability– Inadequate observations

• Implies may be difficult to detect signal

Differences in global ocean heat content between simulations

with/without volcanic forcing1960-2000

Modelled and observed ocean heat content changes are correlated but the observed

signal is larger.

Differences in GMSL between simulations with/without volcanic

forcing 1960-2000

Modelled and observed GMSL changes are correlated but the observed signal is larger.

What are the mechanisms involved?

• Examine Pinatubo response in the model– Best agreement with observations– Best observations

• Look at global ocean heat budgets

• Ensemble averages

Surface ocean heat fluxes for the Pinatubo eruption (1991)

Surface ocean heat fluxes for the Pinatubo eruption (1991)

Surface ocean heat fluxes for the Pinatubo eruption (1991)

Differences in GMSL between simulations with/without volcanic forcing for the Pinatubo eruption

Differences in GMSL between simulations with/without volcanic forcing and Levitus’ steric heights for the Pinatubo eruption

Differences in global ocean heat content between simulations with/without volcanic

forcing for the Pinatubo eruption

Differences in global ocean heat content between simulations with/without volcanic forcing and Levitus’ heat content for the

Pinatubo eruption

Conclusions• Large heat content variations

– order 3 x 1022 J in models, same order but smaller than previous controversial estimates of ocean heat content variability

• Sea level falls of order 5 mm (potentially larger) following volcanic eruptions

• Evaporation changes – same order as interannual variations in global land precipitation

• Small deceleration of heat-content increase and sea-level rise

• Post Pinatubo recovery in sea level occurs during modern satellite record

• Longer term impacts (deeper signals)• T/S signals in ocean and their impact

Title slide

Mt Pinatubo eruption in the Philippines, June 15, 1991.

Gases and solids injected 20 km into the stratosphere.

Reconstructed global average sea level for the period 1950 to 2000