Southern Hemisphere Climate Change: Observations and Projections

1. Southern Hemisphere Climate Change Professor Matthew England Climate and Environmental Dynamics Laboratory School of Mathematics, Faculty of Science The University of New South Wales

2. 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

3. Increase in Atmospheric CO2 Since the Beginning of the Industrial Era

4. 2004 1959 290 190 CO2 Concentration is Rising 2000 1000 1200 1600 1800 1400

5. Radiative forcing in year 2000 relative to pre-industrial

6. NH air temperatures since 1000 A.D.

9. Is the Southern Ocean changing? … observations Larsson-B Ice Shelf Collapse 31 January to 7 March 2002 http://nsidc.org/iceshelves/larsenb2002/animation.html

10. West Antarctic Ice Sheet Oppenheimer (Nature 1998)

11. Twentieth Century Land-Ice Changes Davis et al., Vaughan; Science, 2005

12. Melting of the Greenland Ice-sheet

13. Arctic Sea-ice melting ~10% decrease in sea-ice per decade 1990 2000

14. Ice Age Climate Today’s Climate

15. Antarctic Bottom Water

16. Rintoul 2006

17. 0.017 psu Rintoul 2006

18. .015 .008 .009 Rintoul 2006

19. 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

20. Intermediate depth waters in both hemispheres have become cooler and fresher in recent decades. Wong et al., 1999

21. 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. 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).

22. Australian rainfall trend, 1950 – present day

23. Australian temperature trend, 1950 – present day

24. Southern Hemisphere Jet Stream

25. Changing Southern Hemisphere climate: the Southern Annular Mode Sen Gupta & England 2006

26. Southern Annular Mode

27. Roaring Forties / Furious Fifties

28. Southern Annular Mode

29. Southern Annular Mode … trend due to ozone delpletion & greenhouse gas increases

30. Northern Annular Mode

31. Regression of the Southern Annular Mode onto rainfall ‘Observed’ Model Sen Gupta & England 2006

32. July Zonal Wind (200 hPa) 1949-1968 1975-1994 difference Pandora Hope IOCI

33. How much will the Southern Hemisphere change in the future? … models

34. Climate Modelling Governing equations Forcing conditions Initial conditions Model output

35. 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

40. 5.8 IPCC high and low projection 1.4 Spörer minimum Maunder minimum Dalton minimum 2100 The Past and the Future • Instrumental Data • Proxy Reconstructions • Model Simulations ∆T 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 Year 1500 2000 500 1000

41. 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).

42. 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.

43. Climate Change simulation to year 2054

44. CONTROL 2050 Figure 1. Model Simulation of Trend in Hurricanes (from Knutson et al, 2004)

46. 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

47. Southern Hemisphere Climate Change Professor Matthew England Climate and Environmental Dynamics Laboratory School of Mathematics, Faculty of Science The University of New South Wales