7 th SPC HOF meeting

1. 7th SPC HOF meeting Observed and projected changes to Pacific surface climate Janice Lough (AIMS) Jerry Meehl (NCAR) and Jim Salinger (NZ)

2. OUTLINE • climate – type of weather we expect • surface climate of the Pacific • climate change not a future event • projecting the future and uncertainties • summary AIMS: Australia’s tropical marine research agency

3. NOAA National Climatic Data Center, State of the Climate: Global Analysis for December 2010, published online January 2011, retrieved on February 10, 2011 from www.ncdc.noaa.gov.sotc

4. Complexity of global climate Global annual mean energy budget (2000-2004) W m-2 • all about movement of energy • more energy trapped in climate system Trenberth et al 2009

5. Tropical Pacific • heat engine of atmosphere • vast ocean dominates island climates • trade winds • convergence zones • Walker and Hadley circulations

6. Average sea surface temperature climate (1950-2007) • west to east gradient • dominates island temperature • maximum >30oC in WPWP • minimum > threshold for coral reef growth • small annual range < 2oC

7. Seasonal cycle of winds, rainfall and temperatures

8. Tropical cyclones major destructive weather events • rare within 5-10o of equator • main influence in summer months • average maximum ~ Vanuatu TC Yasi February 2011

9. El Niño-Southern Oscillation (ENSO) McPhaden 2004 • major source of inter-annual climate variability • centred in tropical Pacific • evolves over 12-18 months

10. Typical El Niño and La Niña SST anomalies Large area warmer Large area cooler

11. Typical El Niño and La Niña rainfall anomalies Wetter or drier depending on location

12. ENSO shifts in SPCZ and tropical cyclones El Niño • SPCZ average (black) • SPCZ further north El Niño (red) • SPCZ further south La Niña (blue) La Niña • fewer TCs and further east El Niño • more TCs and further west La Niña

13. Decadal modulation of Pacific surface climate (PDO) • cooler phase SPCZ displaced SW & ENSO variability stronger • warmer phase SPCZ displaced NE & ENSO variability weaker

14. Results in average seasonal climate and variability i.e. what we expect at given place and time of year 1951-1980 monthly temperature and rainfall averages (data source: NIWA)

15. 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

16. 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

17. NATURAL greenhouse effect sustained life on earth – without it ~30oC cooler! More greenhouse gases trap more energy and warm planet

18. Observed and projected increases in carbon dioxide • Mauna Loa and Kiribati • 2010 390ppm • + 40% since 18th century • possible increase by 2100 • tracking high emissions Sources: World Data Centre for Greenhouse Gases; Meehl et al 2007

19. Observed warming of global temperatures • 10 of warmest years since 1998

20. Rate of warming accelerating (1988-2007)- (1950-1969) • warming of Pacific not uniform

21. Climate is about averages & includes variability One swallow does not a summer makeAristotle • tropical oceans warming ~70% of global average

22. Projecting future climates • NEED • high quality observations of climate and forcing factors • understanding of complex physics of global climate system • reliable modelling of climate • projecting future trajectories of greenhouse gases • “downscaling” to relevant spatial scales “Explosion” of Uncertainties

23. Projected Pacific surface temperature warming • multi-model averages • similar magnitude in short term • larger differences in magnitude in long term • the future will be WARMER IPCC 2007

24. Projected Pacific rainfall changes • more uncertainty • similar short term • wetter convergence zones (blue) • drier subtropics (orange) • ± 5% but does not mean no change (grey) • warmer = stronger hydrological cycle • more extreme wet years • more intense droughts IPCC 2007

25. Possible new climates

26. Summary projected changes • low and high emissions similar in short term but larger differences in long term • warming will continue 0.5-1.0oC warmer by 2035 and 1-1.5oC (low) to 2.5-3oC(higher) by 2100 • rainfall more uncertain but likely  in convergence zones &  in subtropics • BUT warmer oceans = stronger hydrological cycle • more extreme rainfall events • warmer air temperatures = more intense droughts • maybe fewer TCs but those that occur more intense • UNCLEAR how ENSO might change

27. SUMMARY • future will be warmer • some islands wetter & some drier • more frequent and more intense extreme weather events • importance of RATE of change • not just new climate regime • for foreseeable future climate will be CHANGING

28. Thank you Warming of the climate system is unequivocal... (IPCC 2007) Most of the observed increase...is very likely due to the observed increase in anthropogenic greenhouse gas concentrations” (IPCC 2007) ...volume of literature in refereed international journals relating to small islands and climate change since publication of the TAR is rather less than that between the Second Assessment Report in 1995 and the TAR in 2001 Mimura et al (2007) Many aspects of tropical climatic responses remain uncertain Christensen et al. (2007) j.lough@aims.gov.au