Changes in surface climate of the tropical Pacific Janice Lough

S. Arrhenius Philosophical Magazine and Journal of Science 1896 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) CO2 290 ppm 0.7oC cooler20cm lower sea level0.1 higher ocean pH75% fewer people

Our climate will be changing for foreseeable future 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

Redistributing sun’s energy = climate system Global annual mean energy budget W m-2 Trenberth et al 2009 without atmosphere Earth ~30oC cooler more greenhouse gases trap more energy in climate system

Pacific atmospheric circulation heat engine ocean dominates island climates trade winds convergence zones Fiji sensitive to SPCZ position Walker and Hadley circulations

Sea surface temperature climate

Seasonal cycles: wind, rainfall, temperature Winds Rain Temperature

Tropical cyclones: destructive weather events TC Jasmine Feb 12 2012

El Niño-Southern Oscillation (ENSO) major source year-year climate variations centred in tropical Pacific evolves over 12-18 months seasonal forecasts

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

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

ENSO shifts SPCZ and tropical cyclones El Niño further north El Niño further south La Niña La Niña fewer cyclones further east El Niño more cyclones further west La Niña

Climate also varies on decadal timescales Pacific Decadal Oscillation (PDO) cooler: SPCZ displaced SW & ENSO variability stronger warmer: SPCZ displaced NE & ENSO variability weaker

Results in average seasonal climate what we expect = climate includes variability (range) what we get = weather

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

Measured increase in carbon dioxide 18th century = 280ppm air bubbles in ice cores 2011= 391ppm Mauna Loa

Observed warming of global temperatures PCCSP 2011 Suva

Observed warming of tropical oceans

Range of possible futures Projecting future climates Scenario IPCC-AR4 (2007) Temperature (oC) CO2 (ppm) Low emissions (B1) +1.8 (1.1-2.9) 450-500 High emissions (A2) +3.4 (2.0-5.4) 750-800 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

Projected surface temperature warming averages from several models spatial difference in magnitude the future will be WARMER

Projected rainfall changes wetter convergence zones drier subtropics more extreme wet years more intense droughts

Preparing for TC Jasmine Vanuatu 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 Preparing for TC Jasmine Vanuatu

Possible new climates Temperature oC Now 2035 2050 2100 Rainfall mm Tarawa 28.2 28.9 29.9 31.4 Funafuti 28.0 28.7 29.4 30.9 Nadi 25.6 26.3 27.0 28.5 Raratonga 23.9 24.6 25.3 26.6 Pitcairn 20.9 21.6 22.1 22.8 Rainfall mm Now 2035 2025 2100 Tarawa 725 780 800 835 Funafuti 1,160 1,250 1,340 Nadi 785 900 Raratonga 425 460 490 Pitcairn 380 350 320

For foreseeable future climate will be CHANGING 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

Challenge of staying below +2oC warming! Peters et al 2012

Thank you j.lough@aims.gov.au