Where is Our SWWA Climate Headed?

1. Where is Our SWWA Climate Headed? Bryson C. Bates Director, CSIRO CLIMATE

2. Talk Outline • Background • GHG emissions • Time scale and context • Planning for climate change • Scenarios • Global climate models (GCMs) • Climate change scenarios for SWWA • Concluding remarks

3. GHG Emissions • CO2 concentrations have grown from 280 ppm in 1750 to 375 ppm in 2003 • Half of CO2 emitted by human activities absorbed by oceans & biosphere, leaving half in atmosphere where it has a lifetime of 50 to 100 years • Impossible to stabilise GHG concentrations at current level • Stabilization at 450 ppm requires reductions of 40% by 2050 & 60% by 2090, limiting global warming to 1.2 to 2.3 ºC by 2100 • Regardless of reductions in GHG emissions, some climate change is inevitable

4. Time Scale & Context • Super-greenhouse conditions have existed before – well before advent of humans • Estimates of arrival time for next ice age vary from 100s to 20,000 years • Population: 5M@35,000BC; 1.2B@1850; 2.5B @1950; 5.3B@1990; 6.3B@2000; 10B by 2050? • In 200 years, world's urban population has grown from 2% to nearly 50% • Megacities: 4@1975, 19@2000, 23@2015? • Infrastructure designed on assumption of a stationary climate

5. Planning for Climate Change • Rather than extrapolating observed trends, we use computer models of climate system driven by scenarios of GHG & aerosol emissions, & ozone depletion • Future GHG emissions will depend on demographic, economic, technological, & political factors that are likely to evolve discontinuouslyin coming decades • Reliable prediction of Australia’s climate over next few decades is impossible • Better not to select one future & hope it comes to pass, nor to find the most probable future & adapt to it

6. Scenarios • Series of events that could lead from the present to plausible but not assured future situations • Exemplify what might happen with/without actions to reduce GHG emissions • Provide baseline against which need for, and effectiveness of, adaptation measures & emission reductions can be measured • Not the same as predictions or forecasts! • Usually consider at most 6 to 7 scenarios (e.g. likely, pessimistic, optimistic) • Acknowledge presence of uncertainty

7. IPCC SRES Scenarios • A2 – population growth to 15 billion by 2100; rather slow economic and technological development • B2 – population growth to 10.4 billion by 2100; more rapidly evolving economy and more emphasis on environmental protection There are also 5 IPCC CO2 stabilisation scenarios (450-1000 ppm)

8. Global Warming Scenarios 5.8 2.9 2.3 1.5 1.4 1.2 50% of uncertainty due to GCMs; 50% to emission scenarios

9. Global Climate Models • Main components: atmosphere, land surface, biosphere, oceans, and polar ice • Simulate water & energy fluxes at 30-minute time steps over 3-D computational grid

10. A Perspective on GCMs • Current GCMs do good job at simulating most of essential climate-forming processes in atmosphere & oceans, & behaviour of total climate system at global scale • Best GCMs not yet sophisticated enough to capture all of the processes that influence climate at regional scales • We have several well-tested technologies for inferring climatic information at local & regional scales from GCM simulations

11. IPCC SRES Scenarios Scenarios used: A2, A1B & B1

12. May to October SRES 450 ppm 550 ppm 2030 2070 November to April Mean Temp: 9 GCMs

13. May to October SRES 550 ppm 450 ppm 2030 2070 November to April Precipitation: 9 GCMs

14. May to October SRES 550 ppm 450 ppm 2030 2070 November to April Potential Evaporation: 7 GCMs

15. L 1012 1016 1020 1016 1012 H Some Weather Types L 1012 .2 .4 .6 .8 1 3 1016 H H Type 1016 1012 1004 1000 1008 5 .2 .4 .6 .8 1 Type

16. Probabilities 1958 - 2003

17. Coupled GCM Runs • CSIRO Mk 3 AGCM: T63 (1.875o x 1.875o approx); 18 vertical levels • OGCM: 1.875o longitude x 0.9375o latitude; 31 vertical levels • Transient run (380 years): observed GHG forcing 1871-present; A2 SRES scenario to 2100; stable GHG 2100-2250 • Control run (323 years): 330 ppm equivalent CO2 for 1871-2193; no other historical forcing

20. Margaret River Current rainfall decrease, as recorded by speleothem P, is well-outside range of natural rainfall variability of last 200 years

21. A New Way of Thinking! • Climate is non-stationary: changed rapidly in the past; changing now; & will change in the future • Future climate will exhibit wet and dry periods due to natural variability – this variability will be superimposed upon continued warming & changes in mean rainfall • We cannot wait for full scientific certainty: it may never come, or it may be too late! • We must take a balance of evidence approach for the time being (just like medical science)

22. A New Way of Thinking! • Mitigation & adaptation are necessary & complementary • Developing policies & plans that are robust across a range of plausible futures will improve environmental, food & water security • Planning for the future can lead to beneficial outcomes in the present • We need to find fair & cost-effective measures to minimise adverse impacts & maximise benefits (must consider communities, not just economics)

23. Awareness Adaptation Abatement Action 13-17 November 2005, Melbourne www.greenhouse2005.com

24. The End