Changes in surface climate of
the tropical Pacific
Janice Lough
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
Key messages
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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
• fewer cyclones further east El Niño
• more cyclones further west La Niña
La Niña
Climate also varies on decadal timescales
c
3
PDO index
2
1
0
-1
-2
-3
1871
1891
1911
1931
1951
1971
1991
Year
• 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
Projecting future climates
Scenario
IPCC-AR4 (2007)
Low emissions (B1)
High emissions (A2)
Temperature (oC)
CO2 (ppm)
+1.8 (1.1-2.9)
+3.4 (2.0-5.4)
450-500
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
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
28.2
28.0
25.6
23.9
20.9
28.9
28.7
26.3
24.6
21.6
29.9
29.4
27.0
25.3
22.1
31.4
30.9
28.5
26.6
22.8
Rainfall mm
Now
2035
2025
2100
Tarawa
Funafuti
Nadi
Raratonga
Pitcairn
725
1,160
785
425
380
780
800
1,250
835
1,340
900
490
320
Tarawa
Funafuti
Nadi
Raratonga
Pitcairn
460
350
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