Transcript Southern Hemisphere Climate Change Professor Matthew England

Southern Hemisphere Climate Change
Professor Matthew England
Climate and Environmental Dynamics Laboratory
School of Mathematics, Faculty of Science
The University of New South Wales
Outline
• Observed 20th Century changes in the
Southern Hemisphere climate system
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Temperature
Rainfall
Land ice, ice shelves, and sea-ice
Ocean properties
Winds and extratropical weather systems
• Projected changes
Increase in Atmospheric CO2 Since the Beginning
of the Industrial Era
CO2 Concentration is Rising
2004
1000
290
190
1200
1400
1600
1800
2000
1959
Radiative forcing in year 2000 relative to pre-industrial
NH air temperatures since 1000 A.D.
Is the Southern Ocean changing?
… observations
Larsson-B Ice Shelf Collapse 31 January to 7 March 2002
http://nsidc.org/iceshelves/larsenb2002/animation.html
West Antarctic Ice Sheet
Oppenheimer (Nature 1998)
Twentieth Century Land-Ice Changes
Davis et al., Vaughan; Science, 2005
Melting of the Greenland Ice-sheet
Arctic Sea-ice melting
1990
2000
~10% decrease in sea-ice per decade
Ice Age Climate
Today’s Climate
Antarctic Bottom Water
Rintoul 2006
115E, 61S to 63.3S
1995
2005
0.1
0
THETA
-0.1
-0.2
.27
8
2
-0.3
-0.4
35
28 .
.30
8
2
-0.5
0.017 psu
34.655 34.66 34.665 34.67 34.675 34.68 34.685 34.69 34.695
Rintoul 2006
SALINITY
115E, 56.5S to 61S
1
1970
1995
2005
0.5
THETA
.008
.015
.009
0
.27
8
2
35
28 .
.30
8
2
-0.5
34.64 34.65 34.66 34.67 34.68 34.69 34.7
SALINITY
34.71 34.72 34.73 34.74
Rintoul 2006
Causes of fresher shelf water
• Increased glacial ice
melt?
• More precipitation?
• Less sea ice
formation?
• Change in winds and
ocean circulation?
Davis et al., Vaughan; Science, 2005
Intermediate depth waters in both hemispheres
have become cooler and fresher in recent decades.
Wong et al., 1999
Observations of temperature at intermediate depths
show a greater than expected warming at high
latitudes and a cooling at mid-latitudes of the
Southern Ocean over the last 50 years (Gille 2002).
Figure 3 from Gille, S. T., 2002.
Warming of the Southern Ocean
since the 1950s. Science, 295,
1275-1277.
Temperature trends between
700 and 1100 m depth from
ALACE floats.
Australian rainfall trend, 1950 – present day
Australian temperature trend, 1950 – present day
Changing Southern Hemisphere climate:
the Southern Annular Mode
Sen Gupta & England 2006
Southern Annular Mode
Roaring Forties / Furious Fifties
Southern Annular Mode
Southern Annular Mode
… trend due to ozone delpletion & greenhouse gas increases
Northern Annular Mode
Regression of the Southern Annular Mode
onto rainfall
Model
‘Observed’
Sen Gupta & England 2006
July Zonal Wind (200 hPa)
1949-1968
1975-1994
difference
Pandora Hope IOCI
How much will the Southern
Hemisphere change in the future?
… models
Climate Modelling
Governing equations
Forcing
conditions
Initial conditions
Model output
Models of the ocean and
atmosphere
• Solve governing equations over a discrete
grid
• Use (sparse) observations in forcing functions
• Integrate solutions forward in time
• Assess simulation vs. observed fields
5.8
The Past and the Future



Instrumental Data
Proxy Reconstructions
Model Simulations
IPCC high
and low
projection
Spörer
minimum
1.4
Maunder Dalton
minimum minimum
∆T
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
Year
500
1000
1500
2000 2100
Climate change appears to be buffered by the Southern Ocean THC
Annual-mean temperature change predicted for ~ the year 2050 in
the GFDL coupled climate model experiment (Manabe et al. 1989).
Annual-mean temperature change predicted for 2070-2100
in IPCC Third Assessment Report models
Annual mean change in temperature (colour shading) and its range (isolines) (Unit: °C) for the SRES
scenario A2, showing the period 2071 to 2100 relative to the period 1961 to 1990.
Climate Change simulation to year 2054
CONTROL
2050
Figure 1. Model Simulation of Trend in Hurricanes
(from Knutson et al, 2004)
CONCLUSIONS
• The Southern Hemisphere, like the antipodes,
have undergone substantial climate change in the
past century
• A manifestation of climate change can be easily
found in Southern Hemisphere air temperatures,
rainfall, ocean properties, land-ice, sea-level,
winds, and storm tracks
• Models suggest these changes will continue for
centuries even with relatively aggressive response
strategies
Southern Hemisphere Climate Change
Professor Matthew England
Climate and Environmental Dynamics Laboratory
School of Mathematics, Faculty of Science
The University of New South Wales