Southern Hemisphere Climate Change Professor Matthew England Climate

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 20 th Century changes in the Southern Hemisphere climate system » » » Temperature Rainfall Land ice, ice shelves, and sea-ice Ocean properties Winds and extratropical weather systems • Projected changes

Increase in Atmospheric CO 2 Since the Beginning of the Industrial Era

CO 2 Concentration is Rising 2004 1000 290 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/larsenb 2002/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

0. 017 psu Rintoul 2006

. 008 . 015. 009 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 1950 s. 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 h. Pa) 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 p Proxy Reconstructions p Model Simulations p IPCC high and low projection Spörer minimum 1. 4 Maunder Dalton 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 A 2, 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