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 CO 2 concentrations have grown from 280 ppm in 1750 to 375 ppm in 2003 Half of CO 2 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 discontinuously in 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 CO 2 stabilisation scenarios (450-1000 ppm)

8. Global Warming Scenarios 1.2 1.4 1.5 2.3 2.9 5.8 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. Mean Temp: 9 GCMs SRES 550 ppm 450 ppm May to October November to April 2030 2070

13. Precipitation: 9 GCMs SRES550 ppm450 ppm May to October November to April 2030 2070

14. Potential Evaporation: 7 GCMs SRES550 ppm450 ppm May to October November to April 2030 2070

15. Some Weather Types 1016 1000 1012 1008 1016 1004 1012 Type 5 3.2.41.8.6.2.4.61.8 H H L

16. Probabilities 1958 - 2003

17. Coupled GCM Runs CSIRO Mk 3 AGCM: T63 (1.875 o x 1.875 o approx); 18 vertical levels OGCM: 1.875 o longitude x 0.9375 o 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 CO 2 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. 13-17 November 2005, Melbourne www.greenhouse2005.com AwarenessAdaptationAbatementAction

24. The End