Changes in surface climate of the tropical Pacific
Based on…….
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
Main climate features of the region
Pacific atmospheric circulation
• Trade winds
• Convergence zones
• Walker and Hadley circulations
Sea surface temperature
El Niño-Southern Oscillation (ENSO)
• Major source year-to-year climate variations
Typical El Niño and La Niña rainfall anomalies
Wetter (green) or drier (orange)
Typical El Niño and La Niña rainfall
Annual rainfall - Apia
Temperature
Effects of El Niño and La Niña on SST
Warmer (red) or cooler (blue)
ENSO shifts SPCZ and tropical cyclones
El Niño
La Niña• Further north El Niño • Further south La Niña
• Fewer cyclones and they are further east El Niño
• More cyclones and they are further west La Niña
Cyclones
Projected changes in climate
Global annual mean energy budget W m-2
Redistributing sun’s energy = climate system
• Without the atmosphere the Earth would be ~30oC cooler• More greenhouse gases trap more energy in climate system
Trenberth et al 2009
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 = 280ppmair bubbles in ice cores
2011= 391ppmMauna Loa
Observed warming of global temperatures
Projecting future climatesEmissions ScenarioIPCC-AR4
(2007)
Temperature (oC) Rainfall
2035 2050 2100 2035 2050 2100
Low (B1)450-500 ppm CO2 0.5-1.0 ? 1.0-1.5 5-15% 10-20% 10-20%
High (A2)750-800 ppm CO2 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
Preparing for TC Jasmine Vanuatu
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
Extremes
• Extremes will become more extreme
• Unclear how ENSO will change – continued influence
Important points to note
•Not just a ‘new climate’ to which we can adapt…….
For foreseeable future, climate will be CHANGING
Summary