1. Changes in surface climate of the tropical Pacific

2. Based on…….

3. Outline and key messages
Main features of region’s climate system
We are affecting the climate system - climate is already changing
Future will be warmer
Extreme weather likely to be more extreme
Our climate will be changing for foreseeable future

4. Main climate features of the region

5. Pacific atmospheric circulation
Trade winds
Convergence zones
Walker and Hadley circulations

6. Sea surface temperature

7. El Niño-Southern Oscillation (ENSO)
Major source of year-to-year climate variations

8. Typical El Niño and La Niña rainfall patterns
Wetter (green) or drier (orange)

9. Typical El Niño and La Niña rainfall
Annual rainfall – Pehnryn

10. Typical El Niño and La Niña temperature
Annual temperature – Rarotonga

11. Effects of El Niño and La Niña on SST
Warmer (red) or cooler (blue)

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. Cyclones in Cook Islands
Number of cyclones passing within 400 km of Rarotonga

14. Projected changes in climate

15. Redistributing sun’s energy = climate system
ADD digram
Without the atmosphere the Earth would be ~30oC cooler
More greenhouse gases trap more energy in climate system

16. 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

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

18. Observed warming of global temperatures

19. Projecting future climates
Emissions Scenario
IPCC-AR4
(2007)
Temperature (oC)
Rainfall
2035
2050
2100
Low (B1)
ppm CO2 ?
5-15%
10-20%
High (A2)
ppm CO2
5-20%
Predicting future forcing – how much more greenhouse gases?
Range of possible futures but the future will be WARMER

20. Spatial variation in warming

21. Cook Island’s temperature projections
Northern Group - increase in temperature of 0.5 – 0.9oC
Southern Group - increase in temperature of 0.4 –1.0oC
More hot days and warm nights
Decline in cooler weather.

22. Spatial variation in rainfall

23. Cook Island’s rainfall projections
Uncertainty around rainfall because model results are not consistent but generally projected to increase
For the Southern Group, average rainfall during the wet season is expected to increase due to intensification of SPCZ
Droughts are projected to become less frequent throughout this century
Reasons for moderate (bordering on high) confidence in wet season rainfall increase:
Positive: An increase in wet season rainfall is consistent with the projected likely increase in the intensity of the South Pacific Convergence Zone (SPCZ), which lies over Vanuatu in this season (the majority of CMIP3 models show a stronger SPCZ)
Positive: Models get SPCZ in the correct location relative to Vanuatu
Negative: Models aren’t as good at rainfall as they are at temperature
Reason for moderate confidence in dry season rainfall increase:
Positive: Approximately half of the CMIP3 models agree on this direction of change by 2090 (depending on exactly which emission scenario you look at)
Negative: In simulations of the current climate, some CMIP3 models have an SPCZ that extends too far east during the dry season, with too much rainfall over Vanuatu (Brown et al., 2011).
Reason for low confidence in annual rainfall increase:
Projections of annual mean rainfall tend to be equally divided between an increase (>5%) and little change (-5% to 5%) by 2090, with only a few models simulating a decrease (<-5%).
There is only moderate and low confidence in the range and distribution of wet and dry season rainfall projections respectively, as discussed above.
Reasons for high confidence in extreme rainfall increase:
An increase in the frequency and intensity of extreme rainfall is consistent with larger-scale projections, based on the physical argument that the atmosphere is able to hold more water vapour in a warmer climate (Allen and Ingram, 2002; IPCC, 2007). It is also consistent with the projected likely increase in the intensity of the SPCZ (Volume 1, Section 6.4.5).
Reasons for low confidence in drought projections:
There is only low confidence in the range of dry season rainfall projections (Section ), which directly influences projections of future drought conditions.

24. 02/03/11
02/03/11
Cyclones
Cook Islands projections indicate there is likely to be a decrease in the number of tropical cyclones by the end of the 21st century
But there is likely to be an increase in average maximum wind speed of cyclones by between 2% and 11%
A list of the projections being delivered in the PCCSP. 24

25. 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

26. Important points to note
Extremes will become more extreme
Unclear how ENSO will change – continued influence

27. For foreseeable future, climate will be CHANGING
Summary
Not just a ‘new climate’ to which we can adapt…….
For foreseeable future, climate will be CHANGING