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  1. 1. Climate science overview Kevin Hennessy Melbourne, 5 June 2006 www.csiro.au
  2. 2. Outline • Evidence for climate change Projections for the 21st century • • Potential impacts • Conclusions
  3. 3. Outline • Evidence for climate change Projections for the 21st century • • Potential impacts • Conclusions
  4. 4. Climate has always been variable. Ice ages occur every 100,000 years due to wobbles in the Earth’s orbit. Greenhouse gases and ice sheets enhance the orbital effect on temperature by about 50% Carbon dioxide and temperature last 420, 000 years 350 20 temperature ( C) 300 o CO2 (ppm) ? 250 10 200 0 150 -10 100 400,000 300,000 200,000 100,000 0 years before present The present CO2 level of 380 ppm is unprecedented in at least the past 420,000 years and it is expected to rise to 550-950 ppm by the year 2100 Temperatures may rise by 1.4-5.8oC by 2100
  5. 5. In the past 200 years, concentrations of greenhouse gases have continued to increase, and the Earth has warmed. This is the enhanced greenhouse effect The main greenhouse gases are water vapour, carbon dioxide, methane, nitrous oxide, ozone and CFCs Carbon dioxide and temperature last 1000 years Cape Grim and South Pole 350 temperature ( C) Law Dome ice cores 1.0 temperature change o CO2 (ppm ) 300 0.5 250 0.0 -0.5 200 1000 800 600 400 200 0 years before 2000 AD Since 1750, carbon dioxide has risen 35%, methane 151%, nitrous oxide 17%, tropospheric ozone 36% The temperature of the late 20th century is the highest in at least the past 1000 years
  6. 6. In the past 100 years, global average surface temperatures have risen 0.7ºC Difference from 1961-1990 average (oC) 1860 1880 1900 1920 1940 1960 1980 2000 The 12 warmest years on record have occurred since 1990 (WMO, 2005)
  7. 7. Over the past 50 years, global average sea-level has risen 9 cm (1.85 mm/year) Source: Church et al (2004)
  8. 8. Other evidence • Warming of the upper 300 m of ocean • Warming in the lowest 8 km of atmosphere • Increase in extremely high temperatures, decrease in extremely low temperatures • More-intense rainfall and cyclones in many places • Oceans are becoming more acidic due to higher CO2 • Snow cover and ice extent have decreased • Shifts in plant and animal locations and behaviour In Australia • Warming of 0.9oC since 1910, mostly since 1950 • Min temps rising faster than max temps • More heatwaves and fewer frosts • More rain in the north-west, less in south and east since 1950 • Less extreme rainfall in the south and east since 1950
  9. 9. GHGs, aerosols, Solar & volcanic ozone depletion Most of the observed warming over the last 50 years is attributable to www.csiro.au human activities that have increased greenhouse gas concentrations
  10. 10. Causes of Australian climate change • Most of the warming is due to human activities • There is uncertainty about the causes of Australian rainfall trends Increases in the northwest may be due to natural variability and a shift in weather patterns due to increases in northern hemisphere aerosols Decreases in the south may be due to natural variability, increases in greenhouse gases and ozone depletion Decreases in the east are due to an increase in El Niños since 1975, the cause of which is unknown
  11. 11. Outline • Evidence for climate change • Projections for the 21st century • Potential impacts • Conclusions
  12. 12. Climate change projections • Rather than simply extrapolating observed trends, we use computer models of the climate system driven by scenarios of greenhouse gas and aerosol emissions, and ozone depletion • Emission scenarios have various assumptions about demographic, economic and technological change
  13. 13. Climate change projections • Global warming of 0.5-1.2oC by 2030 and 1.2-3.8oC by 2070 • Sea level rise of 3-17 cm by 2030 and 7-50 cm by 2070 In Australia • Warming of 0.5-2oC by 2030 and 1-6oC by 2070 • Less frost and snow, more heatwaves and fires • Less annual total rainfall over southern and eastern mainland Australia, with increases over Tasmania • More frequent and intense droughts • Increases in intensity of rain, floods, tropical cyclones and storm surges
  14. 14. 2030 projections for Victoria Feature Low Global Warming High Global Warming Estimate of Uncertainty Estimate of Uncertainty Change change Annual average temperature +0.5 °C ±0.2°C +1.1°C ±0.4°C Average sea level +3 cm +17 cm Annual average rainfall -1.5% ±5% -3.5 % ±11% Seasonal average rainfall Summer 0 ±6.5% - 0% ±15% Autumn 1.5% ±5% -3.5% ±11% Winter -1.5% ±5% -3.5% ±11% Spring -5% ±5% -11% ±11% Annual average potential evaporation +2.2% ±1.1% +5.0% ±2.5% Annual average number of hot days +1 day +10 days (near coast) (>35°C) + 20 days (inland) Annual average number cold nights -1 day -10 days (inland) (<0°C) - 20 days (highlands) Annual average number of very high +1 day +11 days b & extreme forest fire danger days Extreme daily rainfall intensity (1 in +5% +70% c 20 year event) Carbon dioxide concentration +73ppm +102ppm b Results for 2020 C Results for 2050 For risk assessment, it is important to consider extreme scenarios, even though they may have low probability (this is why we have insurance). Note the high global warming including the uncertainty, e.g. annual average rainfall may decline by almost 15% and evaporation may rise by 7.5%
  15. 15. Outline • Evidence for climate change • Projections for the 21st century • Potential impacts • Conclusions
  16. 16. Potential impacts without adaptation Key conclusions for Australia • Most vulnerable ecosystems are wet tropics, Kakadu, alpine areas, coral reefs, freshwater wetlands, and heathlands in south-western Australia • Generally less stream flow in southern and eastern Australia • Crops may benefit from warmer conditions and higher CO2 but this may be offset by reduced rainfall • Greater exposure of infrastructure to extreme weather events and sea-level rise • Greater exposure to heat-related deaths and dengue fever A few examples follow for Victoria
  17. 17. Water Water resources are likely to be further stressed due to projected growth in demand and climate-driven changes in supply for irrigation, cities, industry and environmental flows A decrease in annual rainfall with higher evaporative demand leads to a decrease in run-off into rivers, i.e. a decline of 0-45% by 2030 in 29 Victorian catchments. For Melbourne, average stream-flow is likely to drop 3-11% by 2020 and 7-35% by 2050 Droughts are likely to become more frequent and more severe, with increased fire risk affecting water yield and quality in fire-affected catchments A 10-40% reduction in snow cover is likely by 2020
  18. 18. Heat Victoria is likely to become warmer, with more hot days and fewer cold nights For example, the number of days above 35ºC could average 10-16 in Melbourne (now 9) and 36-50 in Mildura (now 33), while the number of days below 0ºC in Mildura could average 1-4 (now 6) Increased peak summer energy demand for cooling is likely, with reduced energy demand in winter for heating Warming and population growth may increase annual heat- related deaths in those aged over 65, e.g. from 289 deaths at present in Melbourne to 582-604 by 2020 and 980-1318 by 2050 Higher temperatures may also contribute to the spread of vector- borne, water-borne and food-borne diseases
  19. 19. Agriculture Controlled experiments have shown grain yield increases under elevated atmospheric carbon dioxide concentrations. However, it is not known whether this will translate to field conditions in Australia due to nutrient limitations and elevated temperatures. Low to moderate warming may also help plant growth especially frost sensitive crops such as wheat, but more hot days and a decline in rainfall or irrigation could reduce yields. Warmer winters can reduce the yield of stone fruits and apples that require winter chilling. Grape quality is likely to decline. Livestock would be adversely affected by greater heat stress. In forestry, the CO2 benefits may be offset by increased bushfires and changes in pests.
  20. 20. Cities Changes in average climate and sea-level will affect building design, standards and performance, energy and water demand, and coastal planning Increases in extreme weather events are likely to lead to increased flash flooding, strains on sewerage and drainage systems, greater insurance losses, possible black-outs, more fires and challenges for emergency services.
  21. 21. Conclusions Climate change is real and underway Most of the warming of the past 50 years is due to human activities Climate change will continue in the 21st century Warmer and drier conditions are expected, with more extreme events Significant impacts are likely Risk management requires consideration of low probability, high impact scenarios
  22. 22. Thank you