Changes in surface climate of
the tropical Pacific
Presented by
Janice Lough
Authors
This presentation is based on Chapter 2 ‘Observed and
projected changes in surface climate of the tropical Pacific’
in the book Vulnerability of Tropical Pacific Fisheries and
Aquaculture to Climate Change, edited by JD Bell, JE
Johnson and AJ Hobday and published by SPC in 2011.
The authors of Chapter 2 are: Janice Lough, Gerry Meehl
and Jim Salinger
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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•
•
•
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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
NASA
Trenberth et al. (2009) BAMS
• Without the atmosphere, the Earth would be ~30oC cooler
• More greenhouse gases trap more energy the climate system
Pacific atmospheric circulation
• Heat engine
• Ocean dominates island
climates
• Trade winds
• Convergence zones
• Walker & Hadley circulations
Sea surface temperature climate
Seasonal cycles: wind, rainfall, temperature
Winds
Rain
Temperature
Cyclones: destructive weather events
www.ncdc.noaa.gov/oa/ibtracs
TC Jasmine Feb 12 2012
NASA MODIS
www.niwa.co.nz
El Niño-Southern Oscillation (ENSO)
McPhaden (2004)BAMS
• Major source of year-year climate variations
• Centred in tropical Pacific
• Evolves over 12-18 months
• Seasonal forecasts
El Niño and La Niña SST anomalies
Warmer (red) or cooler (blue)
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
www.niwa.co.nz
Climate also varies on decadal timescales
c
3
PDO index
2
1
0
-1
-2
-3
1871
1891
1911
1931
1951
Year
1971
1991
jisao.washington.edu/pdo
• 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
Observed warming of global temperatures
Observed warming of tropical oceans
Projecting future climates (2100)
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
• Future will be WARMER
IPCC AR4 2007
Projected rainfall changes
• Wetter convergence zones
• Drier subtropics
• More extreme wet years
• More intense droughts
IPCC AR4 2007
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)Climatic Change
Preparing for TC Jasmine Vanuatu
Photo: Mohammed Ashiq
Photo: VBTC
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