Changes in surface climate of the tropical Pacific

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Changes in surface climate of the tropical
Pacific
Janice Lough
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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
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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

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Redistributing suns 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

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Pacific atmospheric circulation

• heat engine
• ocean dominates island climates

• trade winds
• convergence zones
• Fiji sensitive to SPCZ position
• Walker and Hadley circulations

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Sea surface temperature climate
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Seasonal cycles wind, rainfall, temperature
Winds
Rain
Temperature
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Tropical cyclones destructive weather events
TC Jasmine Feb 12 2012
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El Niño-Southern Oscillation (ENSO)

• major source year-year climate variations
• centred in tropical Pacific
• evolves over 12-18 months
• seasonal forecasts

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Typical El Niño and La Niña SST anomalies
Warmer (red) or cooler (blue)
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Typical El Niño and La Niña rainfall anomalies
Wetter (green) or drier (orange)
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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

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Climate also varies on decadal timescales

• Pacific Decadal Oscillation (PDO)
• cooler SPCZ displaced SW ENSO variability
  stronger
• warmer SPCZ displaced NE ENSO variability
  weaker

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Results in average seasonal climate

• what we expect climate
• includes variability (range)
• what we get weather

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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
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Measured increase in carbon dioxide
18th century 280ppm air bubbles in ice cores
2011 391ppm Mauna Loa
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Observed warming of global temperatures
PCCSP 2011
Suva
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Observed warming of tropical oceans
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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
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Projected surface temperature warming

• averages from several models
• spatial difference in magnitude
• the future will be WARMER

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Projected rainfall changes

• wetter convergence zones
• drier subtropics
• more extreme wet years
• more intense droughts

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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
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Possible new climates
Temperature oC Now 2035 2050 2100
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
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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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Challenge of staying below 2oC warming!
Peters et al 2012
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Thank you
j.lough_at_aims.gov.au