Changes in surface climate of the tropical Pacific

Presented byJanice 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

“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)

History of human influence on climate: 1896

CO2 290 ppm

0.7oC cooler20cm lower sea level0.1 higher ocean pH75% fewer people

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

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 the climate system

Trenberth et al. (2009) BAMS

NASA

•Heat engine

•Ocean dominates island

climates

• Trade winds

• Convergence zones

• Walker & Hadley circulations

Pacific atmospheric circulation

Sea surface temperature climate

Seasonal cycles: wind, rainfall, temperature

Winds Rain Temperature

Cyclones: destructive weather events

TC Jasmine Feb 12 2012

www.ncdc.noaa.gov/oa/ibtracs

www.niwa.co.nzNASA MODIS

El Niño-Southern Oscillation (ENSO)

• Major source of year-year climate variations

• Centred in tropical Pacific

• Evolves over 12-18 months

• Seasonal forecasts

McPhaden (2004)BAMS

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

La Niña• Further north El Niño • Further south La Niña

• Fewer cyclones further east El Niño• More cyclones further west La Niña

www.niwa.co.nz

Climate also varies on decadal timescales

-3

-2

-1

0

1

2

3

1871 1891 1911 1931 1951 1971 1991

Year

PD

O in

dex

c

• Pacific Decadal Oscillation (PDO)• Cooler: SPCZ displaced SW & ENSO variability stronger• Warmer: SPCZ displaced NE & ENSO variability weaker

jisao.washington.edu/pdo

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 = 280ppmair bubbles in ice cores

Observed warming of global temperatures

Observed warming of tropical oceans

Projecting future climates (2100)ScenarioIPCC-AR4 (2007)

Temperature (oC) CO2 (ppm)

Low emissions (B1) +1.8 (1.1-2.9) 450-500 High emissions (A2) +3.4 (2.0-5.4) 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

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)Climatic Change

Extremes

Photo: Mohammed Ashiq Photo: VBTC

Temperature (oC) Now 2035 2050 2100Tarawa 28.2 28.9 29.9 31.4Funafuti 28.0 28.7 29.4 30.9Nadi 25.6 26.3 27.0 28.5Raratonga 23.9 24.6 25.3 26.6Pitcairn 20.9 21.6 22.1 22.8

Rainfall (mm) Now 2035 2025 2100Tarawa 725 780 800 835Funafuti 1,160 1,250 1,340Nadi 785 900Raratonga 425 460 490Pitcairn 380 350 320

Possible new climates

•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

Summary