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

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

NOAA National Climatic Data Center, State of the Climate: Global Analysis for December 2010, published online January 2011, retrieved on February 10, 2011 from

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

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

Average sea surface temperature climate ( ) west to east gradient dominates island temperature maximum >30 o C in WPWP minimum > threshold for coral reef growth small annual range < 2 o C

Seasonal cycle of winds, rainfall and temperatures

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

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

Typical El Niño and La Niña SST anomalies Large area warmerLarge area cooler

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

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

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

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

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

History of human influence on climate: 1896 “A simple calculation shows that the temperature in the arctic regions would rise about 8 o to 9 o C, 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) CO ppm

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

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

Observed warming of global temperatures Top 10 warmest Years Anomaly °C of warmest years since 1998

Rate of warming accelerating warming of Pacific not uniform ( )- ( )

Climate is about averages & includes variability One swallow does not a summer make Aristotle tropical oceans warming ~70% of global average

Projecting future climates Scenario IPCC-AR4 (2007) Temperature ( o C)CO 2 (ppm) B1+1.8 ( ) A2+3.4 ( ) 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

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

Projected Pacific rainfall changes IPCC 2007 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

Temperature ObservedB1A2B1A2 Tarawa Funafuti Nadi Raratonga Pitcairn DJF rainfall ObservedB1A2B1A2 Tarawa > Funafuti1,1641,222-1,2801,280-1,397 Nadi Raratonga Pitcairn Possible new climates

low and high emissions similar in short term but larger differences in long term warming will continue o C warmer by 2035 and o C (low) to o C (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 Summary projected changes

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

Thank you Warming of the climate system is unequivocal... (IPCC 2007) Many aspects of tropical climatic responses remain uncertain Christensen et al. (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) Most of the observed increase...is very likely due to the observed increase in anthropogenic greenhouse gas concentrations” (IPCC 2007)