Title slide

1
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, USA 4
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.
2
Reconstructed global average sea level for the
period 1950 to 2000
Agung 1963
Mt Pinatubo 1991
El Chichon 1982
3
Radiative forcing of climate
From Ramswamy et al., 2001, IPCC TAR
4
Peaks of -5 W m-2 following major explosive
volcanic eruptions
From Ramswamy et al., 2001, IPCC TAR
5
Different stratospheric loading models
6
PCM 20thC ensembles 1890-1999
4 members each with the following forcings
V volcanic S solar G ghg Su sulfates Oz ozone
SOz solarozone VS volcanicsolar VSOz volcan
icsolarozone GS ghgsulfates GOz ghgozone GSu
Oz ghgsulfatesozone SGSuOz solarghgsulfatesoz
one VSGSuOz volcanicsolarghgsulfatesozone
(ALL)
DOE/NCAR Parallel Climate Model DOE/NCAR Parallel Climate Model
Atmosphere CCM3 T42 18L 2.8 degree
Land LSM
Ocean POP 32L 2/3 degree
Sea-ice Dynamic and thermodynamic
7
Observed concentrations and loadings used to
force the model
8
Simulated GMSL with/without volcanic forcing
1890-2000
9
Differences in GMSL between simulations
with/without volcanic forcing1890-2000
10
Volcanic forcing results in a rapid fall in GMSL
of 5 mm
11
Differences in global ocean heat content between
simulations with/without volcanic forcing1890-2000
12
Volcanic forcing results in a fall in global
average heat content of 3 x 1022 J
13
Much of the heat content changes in the upper 200
m but some deeper signals
14
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

15
Differences in global ocean heat content between
simulations with/without volcanic forcing1960-2000
16
Modelled and observed ocean heat content changes
are correlated but the observed signal is larger.

17
Differences in GMSL between simulations
with/without volcanic forcing 1960-2000
18
Modelled and observed GMSL changes are correlated
but the observed signal is larger.
19
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

20
Surface ocean heat fluxes for the Pinatubo
eruption (1991)
21
Surface ocean heat fluxes for the Pinatubo
eruption (1991)
22
Surface ocean heat fluxes for the Pinatubo
eruption (1991)
23
Differences in GMSL between simulations
with/without volcanic forcing for the Pinatubo
eruption
24
Differences in GMSL between simulations
with/without volcanic forcing and Levitus steric
heights for the Pinatubo eruption
25
Differences in global ocean heat content between
simulations with/without volcanic forcing for the
Pinatubo eruption
26
Differences in global ocean heat content between
simulations with/without volcanic forcing and
Levitus heat content for the Pinatubo eruption
27
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

28
Title slide
Mt Pinatubo eruption in the Philippines, June 15,
1991. Gases and solids injected 20 km into the
stratosphere.
29
Reconstructed global average sea level for the
period 1950 to 2000
30
(No Transcript)
31
(No Transcript)