The impact of climate change on weather variability into the future

1. The impact of climate change on weather variability into the future Kevin Hennessy CSIRO Marine & Atmospheric Research

2. Outline • Communication challenges • Robust findings • Key uncertainties • Victorian projections • Conclusions

3. Communication challenges • Most Australians believe that climate change is real and want to learn more about climate change1 • Information about climate change can be found from a variety of sources, including scientific journals, technical reports, books, media articles and blogs • The messages are not always consistent and the balance is not always appropriate, so it’s hard to know who and what to believe • 1 theconversation.edu.au/what-australians-really-think-about-climate-change-1793

4. The peer-review process • An article without peer-review, such as a newspaper opinion piece, should be treated with caution • Peer-review ensures that published findings are objective and reliable • Without the peer-review system, publication of research findings could be influenced by personal, social or political agendas • Scientific journals have rigorous peer-review and high credibility

5. Reviews based on peer-reviewed literature • The Intergovernmental Panel on Climate Change (2007): Climate Change 2007 Synthesis Report • The Royal Society (2010): Climate Change: A Summary of the Science • The Australian Academy of Science (2010): The Science of Climate Change: Questions and Answers • The Climate Change Commission (2011): The Critical Decade • Vic DSE (2008): Climate change in Victoria – 2008 summary • Vic DSE (in press): Update of climate change science for Victoria

6. Outline • Communication challenges • Robust findings • Key uncertainties • Victorian projections • Conclusions

7. Robust findings • There is clear evidence for global warming and sea level rise

8. Near-surface air temperatures have risen 0.8oC In 2010, global average temperature was 0.53°C above the 1961-90 mean. This is 0.01°C above the value in 2005, and 0.02°C above 1998. 2001-2010 is the warmest decade since the beginning of instrumental climate records http://www.wmo.int/pages/mediacentre/press_releases/pr_906_en.html

9. Global-average sea level has risen 1.7 mm/yr Global averaged sea level from 1880 to 2009 as estimated from coastal and island sea-level data (blue) and from the satellite-altimeter data since 1993 (black). Shading indicates one standard deviation(Church and White, 2011)

10. Robust findings • Ocean acidity has increased due to the uptake of anthropogenic CO2 • Observed changes in many physical and biological systems are consistent with warming IPCC (2007)

11. Robust findings • Climate variability is driven by • Internal processes • Natural cycles, such as the El Nino Southern Oscillation • External factors affect the surface heat balance of the Earth • Natural – variations in solar radiation (orbital wobbles, sunspots), large volcanic eruptions • Anthropogenic (human) – increases in greenhouse gases, aerosols, ozone depletion, land-use change IPCC (2007)

12. Robust findings In the first half of the 20th century, increasing greenhouse gases, increasing solar radiation and a relative lack of volcanic activity all contributed to a rise in globally averaged temperature During the 1950s and 1960s, global temperatures levelled off. This is most likely due to an increase in aerosols from industrialisation after WW2 and the eruption of Mt. Agung in 1963 Since the 1970s, increases in greenhouse gases have dominated over all other factors, and there has been a period of sustained warming Most of the warming since the mid-20th century is very likely (more than 90% confidence) due to anthropogenic increases in greenhouse gases (IPCC, 2007)

13. Robust findings • Discernible human influences: • ocean warming, tropospheric warming and stratospheric cooling, continental-average temperatures, temperature extremes and wind patterns (IPCC, 2007) • less Arctic sea ice, changes in the hydrological cycle, global and regional patterns of precipitation changes, and increases in ocean salinity in the tropical Atlantic (Stott et al., 2010)

14. Robust findings • Global greenhouse gas emissions will continue to grow over the next few decades, leading to further climate change • Anthropogenic warming and sea level rise will continue for centuries even if greenhouse gas emissions were to be reduced sufficiently for atmospheric concentrations to stabilise • Increased frequencies and intensities of some extreme weather events are very likely IPCC (2007)

15. Robust findings • Systems and sectors at greatest risk are ecosystems, low-lying coasts, water resources in some regions, tropical agriculture, and health in areas with low adaptive capacity • The regions at greatest risk are the Arctic, Africa, small islands and Asian and African mega-deltas • Within other regions, even those with high incomes, some people, areas and activities are at risk IPCC (2007)

16. Robust findings • Some adaptation is underway, but more extensive adaptation is needed to reduce vulnerability • Unmitigated climate change would, in the long term, be likely to exceed adaptive capacity • Many impacts can be reduced, delayed or avoided by mitigation • Mitigation over the next two to three decades will have a large impact on opportunities to achieve lower greenhouse gas stabilisation levels IPCC (2007)

17. Outline • Communication challenges • Robust findings • Key uncertainties • Victorian projections • Conclusions

18. Key uncertainties Includes a nice summary of common myths

19. Causes of climate change • Effects of climate changes on human and some natural systems are difficult to detect due to adaptation and non-climatic influences (IPCC, 2007) • Hard to reliably attribute observed climate changes to natural or human causes at smaller than continental scales (Stott et al, 2010)

20. Emission scenarios The IPCC emission scenarios have various assumptions about demographic, economic and technological change IPCC (2007)

21. Climate models • Global climate models have strengths and weaknesses • Confidence in projections is higher for some variables (e.g. temperature) than for others (e.g. rainfall), and it is higher for larger spatial scales and longer averaging periods IPCC (2007)

22. Feedbacks • Models differ in their estimates of the strength of different feedbacks in the climate system, particularly cloud feedbacks, oceanic heat uptake and carbon cycle feedbacks • Positive water vapour feedback well understood, positive feedback from high clouds in all models, low cloud feedback uncertain IPCC (2007)

23. Projected global warming Grey bars include an estimate of the effect of carbon cycle feedback IPCC 2007 Different models give different projections for a given emission scenario

24. Aerosols Change from the year 1750 Direct and indirect aerosol impacts on the magnitude of the temperature response, clouds and precipitation remain uncertain IPCC (2007)

25. Sea level rise Significant uncertainty about contribution from ice-sheets by the year 2100 (Rahmstorf, 2010)

26. Outline • Communication challenges • Robust findings • Key uncertainties • Victorian projections • Conclusions

27. Victorian warming in 2030, 2050, 2070 Ranges represent the lowest 10% and highest 10% of climate model results 2030: 0.6-1.2oC (mid-range emissions) Greater dependence on emissions after 2030 2050: 0.6-1.5oC (low emissions), 1.0-2.5oC (high emissions) 2070: 0.9 to 2.0oC (low emissions), 1.8 to 3.8oC(high emissions) Greater rise in maximum temperature than minimum temperature Slightly more warming in spring and summer than autumn and winter Vic DSE (2008)

28. Extreme daily temperatures in 2030 and 2070 Annual average number of days over 35oC Annual average number of days below 2oC Vic DSE (2008) 5-40% more extreme fire-weather days by 2020 15-50% more extreme fire weather days by 2050 for low emissions 80-230% more extreme fire weather days by 2050 for high emissions Lucas et al (2007)

29. Victorian rainfall change in 2030, 2050, 2070 A tendency for less rainfall 2030: annual average -9 to +1% (mid-range emissions) Greater dependence on emissions after 2030 2050: annual average -10 to +2% (low emissions), -20 to +2% (high emissions) 2070: annual average -14 to +2% (low emissions), -25 to +3% (high emissions) Less rain is likely in winter & spring, with uncertainty about changes in summer & autumn Vic DSE (2008)

30. Exceptionally hot / dry years We defined exceptionally hot / dry low years as occurring once every 20 years on average from 1900-2007 In Vic and Tas, over the period 2010-2040, exceptionally hot years may occur annually, while exceptionally dry years mayoccur once every 12 years on average The area affected may increase from 5% during 1900-2007 to around 75% during 2010-2040 The area affected may increase from 5% during 1900-2007 to around 10% during 2010-2040 Hennessy et al., 2008

31. Heavy daily rainfall projections Heavy rainfall intensity is likely to increase in summer and autumn, with little change in winter and spring Large uncertainty due to differences between climate model results Vic DSE (2008)

32. Other projections for Victoria • Windspeed little change by 2030 • Relative humidity little change by 2030 • Solar radiation increases 0-2% by 2030 • Potential evaporation increases 1-5% by 2030 • Runoff decreases 5-20% by 2030 • Snow decreases 10-40% by 2020 Vic DSE (2008)

33. Impacts, adaptation & mitigation • Impact assessment is hampered by uncertainties surrounding regional climate projections, particularly rainfall • Understanding of low-probability/high-impact events is generally limited • Barriers, limits and costs of adaptation are not fully understood • Estimates of mitigation costs and potentials depend on uncertain assumptions about future socio-economic growth, technological change and consumption patterns IPCC (2007)

34. Outline • Communication challenges • Robust findings • Key uncertainties • Victorian projections • Conclusions

35. Conclusions Navigating the maze of information about climate change science is challenging. Recent assessments of the peer-reviewed literature put this into perspective There are many robust findings about the science. These provide a basis for action through mitigation of greenhouse gases as well as adaptation to reduce our vulnerability to climate change impacts There are also scientific uncertainties. These are quantified where possible and need to be considered in risk management

36. Thank you Kevin Hennessy CSIRO Marine and Atmospheric Research PB 1 Aspendale Victoria, 3195 Phone: +61 3 9239 4536 Email: Kevin.Hennessy@csiro.au

37. Causes of global warming: past 60 yrs The hiatus in warming from 1998-2008 coincides with a period of little increase in the sum of anthropogenic and natural forcings. Declining solar insolation as part of a normal eleven-year cycle, and a cyclical change from an El Nino to a La Nina, dominate our measure of anthropogenic effects because rapid growth in short-lived sulfur emissions partially offsets rising greenhouse gas concentrations. Therefore, recent global temperature records are consistent with the existing understanding of the relationship among global surface temperature, internal variability, and radiative forcing, which includes anthropogenic factors with well known warming and cooling effects. Kaufmann et al (2011: PNAS)

38. The peer review process • Not all scientific books are peer-reviewed. Even though the help of many scientists may be acknowledged, the quality cannot be guaranteed • Major reports are normally peer-reviewed • For example, the Intergovernmental Panel on Climate Change (IPCC) assesses the peer-reviewed literature • About 1250 authors were involved • Comments from over 2,500 scientific expert reviewers and hundreds of government reviewers • Authors addressed every comment to the satisfaction of independent Review Editors • Summary for Policymakers was approved line-by-line by officials from 113 governments