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Changes in surface climate of the tropical Pacific

Changes in surface climate of the tropical Pacific. Presented by Janice Lough. Authors.

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Changes in surface climate of the tropical Pacific

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  1. Changes in surface climate of the tropical Pacific Presented by Janice Lough

  2. Authors This presentation is based on Chapter 2 ‘Observed and projected changes in surface climate of the tropical Pacific’ in the book Vulnerability of Tropical Pacific Fisheries and Aquaculture to Climate Change, edited by JD Bell, JE Johnson and AJ Hobday and published by SPC in 2011. The authors of Chapter 2 are: Janice Lough, Gerry Meehl and Jim Salinger

  3. History of human influence on climate: 1896 “A simple calculation shows that the temperature in the arctic regions would rise about 8o to 9oC, if the carbonic acid increased to 2.5 or 3 times its present value” S. Arrhenius Philosophical Magazine and Journal of Science 1896 (1903 Nobel Prize winner) CO2290 ppm 0.7oC cooler20cm lower sea level0.1 higher ocean pH75% fewer people

  4. Key messages • We are all used to current climate and seasons • Humans affecting climate system • Climate is already changing • Models imperfect but provide possible futures • Future will be warmer • Some places will be wetter and some drier • Extreme weather likely to be more extreme Our climate will be changing for foreseeable future

  5. Redistributing sun’s energy = climate system Global annual mean energy budget W m-2 NASA Trenberth et al. (2009) BAMS • Without the atmosphere, the Earth would be ~30oC cooler • More greenhouse gases trap more energy the climate system

  6. Pacific atmospheric circulation • Heat engine • Ocean dominates island climates • Trade winds • Convergence zones • Walker & Hadley circulations

  7. Sea surface temperature climate

  8. Seasonal cycles: wind, rainfall, temperature Winds Rain Temperature

  9. Cyclones: destructive weather events www.ncdc.noaa.gov/oa/ibtracs TC Jasmine Feb 12 2012 NASA MODIS www.niwa.co.nz

  10. El Niño-Southern Oscillation (ENSO) McPhaden (2004)BAMS • Major source of year-year climate variations • Centred in tropical Pacific • Evolves over 12-18 months • Seasonal forecasts

  11. El Niño and La Niña SST anomalies Warmer (red) or cooler (blue)

  12. El Niño and La Niña rainfall anomalies Wetter (green) or drier (orange)

  13. ENSO shifts SPCZ and tropical cyclones El Niño La Niña • Further north El Niño • Further south La Niña • Fewer cyclones further east El Niño • More cyclones further west La Niña www.niwa.co.nz

  14. Climate also varies on decadal timescales jisao.washington.edu/pdo • Pacific Decadal Oscillation (PDO) • Cooler: SPCZ displaced SW & ENSO variability stronger • Warmer: SPCZ displaced NE & ENSO variability weaker

  15. Results in average seasonal climate • What we expect = climate • Includes variability (range) • What we get = weather

  16. Why are climate scientists so sure climate is changing due to human activities? • Theory • Modelling • Evidence: • instrumental measurements • changes in the physical world • changes in the biological world • paleoclimate archives The climate system appears to be changing faster than earlier thought likely (Steffen 2009)

  17. Measured increase in carbon dioxide 18th century = 280ppm air bubbles in ice cores

  18. Observed warming of global temperatures

  19. Observed warming of tropical oceans

  20. Projecting future climates (2100) • Good observations • Understanding of climate system • Realistic models • Predict future forcing – how much more greenhouse gases? • “Downscaling” to scales that matter to us Range of possible futures

  21. Projected surface temperature warming • Averages from several models • Spatial difference in magnitude • Future will be WARMER IPCC AR4 2007

  22. Projected rainfall changes • Wetter convergence zones • Drier subtropics • More extreme wet years • More intense droughts IPCC AR4 2007

  23. Extremes The answer to the oft-asked question of whether an event is caused by climate change is that it is the wrong question All weather events are affected by climate change because the environment in which they occur is warmer and moister than it used to be Trenberth (2012)Climatic Change Preparing for TC Jasmine Vanuatu Photo: VBTC Photo: Mohammed Ashiq

  24. Possible new climates

  25. Summary • Future will be warmer • Some islands wetter and some drier • Maybe fewer but stronger tropical cyclones • More frequent and stronger extreme weather events • Unclear how ENSO will change – continued influence • Importance of RATE of change • Not just a “new climate” to which we can adapt • For foreseeable future climate will be CHANGING

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