1. Changes in surface climate of the tropical Pacific
Janice Lough

2. 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

3. 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

4. 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

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

6. Sea surface temperature climate

7. Seasonal cycles: wind, rainfall, temperature
Winds
Rain
Temperature

8. Tropical cyclones: destructive weather events
TC Jasmine Feb

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

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

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

12. 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

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

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

15. 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

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

17. Observed warming of global temperatures
PCCSP 2011
Suva

18. Observed warming of tropical oceans

19. Range of possible futures
Projecting future climates
Scenario
IPCC-AR4 (2007)
Temperature (oC)
CO2 (ppm)
Low emissions (B1)
+1.8 ( )
High emissions (A2)
+3.4 ( )
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

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

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

22. 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

23. 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

24. 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

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

26. Thank you