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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 » » » » » 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