Changes in surface climate of
the tropical Pacific
Based on…….
Outline and key messages
• Main features of region’s climate system
• Human influence on 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
Main climate features of the region
Pacific atmospheric circulation
• Trade winds
• Convergence zones
• Walker and Hadley circulations
El Niño-Southern Oscillation (ENSO)
• Major source of year-to-year climate variations
Sea surface temperature & ENSO
Effects of El Niño and La Niña on SST
Warmer (red) or cooler (blue)
Typical El Niño and La Niña rainfall patterns
Wetter (green) or drier (orange)
Typical El Niño and La Niña rainfall
Annual rainfall – Port Vila
Typical El Niño and La Niña temperature
Annual temperature – Port Vila
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
Cyclones in Vanuatu
Number of cyclones passing within 400 km of Port Vila
Tropical Cyclones
Vanuatu 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 the
average maximum wind speed of cyclones by
between 2% and 11% and an increase in
rainfall intensity of about 20% within
100 km of the cyclone centre.
Unclear how ENSO will
change in CC context –
continued influence
CLOUD NASARA
Animation Project, Launch in June/July 2013!
Projected changes in
Vanuatu’s climate
Redistributing sun’s energy = climate system
• Without the atmosphere the Earth would be ~30oC cooler
• More greenhouse gases trap more energy in climate system
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
Projecting future climates
Emissions
Scenario
IPCC-AR4
(2007)
Low (B1)
450-500 ppm CO2
High (A2)
750-800 ppm CO2
Temperature (oC)
2035
2050
0.5-1.0
?
2100
Rainfall
2035
2050
2100
1.0-1.5 5-15% 10-20% 10-20%
0.5-1.0 1.0-1.5 2.5-3.0
5-20% 10-20% 10-20%
• Predicting future forcing – how much more greenhouse
gases?
• Range of possible futures but the future will be WARMER
Spatial variation in warming
Spatial variation in rainfall
Vanuatu’s Rainfall projections
 Wet season rainfall is projected to increase
(moderate confidence)
 Dry season rainfall is projected to decrease
(moderate confidence)
 Annual mean rainfall is projected to
increase (low confidence)
 Rainfall over Vanuatu is strongly influenced
by ENSO
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
Whitegrass
Declining Cool Days and Increasing Warm Days
Warm Days: Percentage of
days when TX>90th percentile
35
35
30
30
25
y = -0.2883x + 14.484
R² = 0.3654
25
20
15
15
10
10
5
5
0
0
1969
1971
1973
1975
1977
1979
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
2003
2005
2007
20
y = 0.4415x + 2.7889
R² = 0.4587
1969
1971
1973
1975
1977
1979
1981
1983
1985
1987
1989
1991
1993
1995
1997
1999
2001
2003
2005
2007
Cool Days: Percentage of days
when TX<10th percentile
Extremes of Vanuatu Temperature & Rainfall
 The intensity and frequency of days of
extreme heat are projected to increase
(very high confidence)
Increase in the number of hot days and
warm nights and a decline in cooler weather.
The intensity and frequency of days of
extreme rainfall are projected to increase
(high confidence)
Little change is projected in the incidence of
drought (low confidence)
Important points to note
• ENSO and climate variability are KEY PART of
Vanuatu’s Climate System
• Human influence on the climate system already
being measured in Vanuatu
• Future will be warmer
• Extreme weather likely to be more extreme
•Not just a ‘new climate’ to which we can adapt…….
For foreseeable future, climate will be
CHANGING
For More Information....
Vanuatu
Meteorology &
Geo-hazards
Department
Tel: 24686