7th SPC HOF meeting

Observed and projected changes to Pacific surface climate

Janice Lough (AIMS)Jerry Meehl (NCAR) and Jim Salinger (NZ)

OUTLINE

• climate – type of weather we expect

• surface climate of the Pacific

• climate change not a future event

• projecting the future and uncertainties

• summary

AIMS: Australia’s tropical marine research agency

NOAA National Climatic Data Center, State of the Climate: Global Analysis for December 2010, published online January 2011, retrieved on February 10, 2011 from www.ncdc.noaa.gov.sotc

Complexity of global climate

Global annual mean energy budget (2000-2004) W m-2

• all about movement of energy

• more energy trapped in climate system

Trenberth et al 2009

Tropical Pacific• heat engine of atmosphere• vast ocean dominates island climates

• trade winds• convergence zones• Walker and Hadley circulations

Average sea surface temperature climate (1950-2007)

• west to east gradient• dominates island temperature• maximum >30oC in WPWP• minimum > threshold for coral reef growth• small annual range < 2oC

Seasonal cycle of winds, rainfall and temperatures

Tropical cyclones major destructive weather events

• rare within 5-10o of equator• main influence in summer months• average maximum ~ Vanuatu

TC Yasi February 2011

El Niño-Southern Oscillation (ENSO)

• major source of inter-annual climate variability• centred in tropical Pacific• evolves over 12-18 months

-3

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1871 1891 1911 1931 1951 1971 1991

Year

std

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T a

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McPhaden 2004

Typical El Niño and La Niña SST anomalies

Large area warmer Large area cooler

Typical El Niño and La Niña rainfall anomalies

Wetter or drier depending on location

• SPCZ average (black)• SPCZ further north El Niño (red)• SPCZ further south La Niña (blue)

ENSO shifts in SPCZ and tropical cyclones

El Niño

La Niña

• fewer TCs and further east El Niño• more TCs and further west La Niña

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1871 1891 1911 1931 1951 1971 1991

Year

PD

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Decadal modulation of Pacific surface climate (PDO)

• cooler phase SPCZ displaced SW & ENSO variability stronger• warmer phase SPCZ displaced NE & ENSO variability weaker

1951-1980 monthly temperature and rainfall

averages (data source: NIWA)

Results in average seasonal climate and variabilityi.e. what we expect at given place and time of year

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

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

NATURAL greenhouse effect sustained life on earth

– without it ~30oC cooler!

More greenhouse gases trap more energy and

warm planet

• Mauna Loa and Kiribati• 2010 390ppm• + 40% since 18th century

• possible increase by 2100• tracking high emissions

Sources: World Data Centre for Greenhouse Gases; Meehl et al 2007

Observed and projected increases in carbon dioxide

y = 0.0044x - 0.5243

R2 = 0.6402-0.6

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1850 1880 1910 1940 1970 2000

year

oC

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e Annual global land & sea temperatures: 1850-2009

(1980-2009)-(1850-1879)= +0.58oC

Data source: HadCRU

Observed warming of global temperatures

Top 10 warmest

Years Anomaly °C

2010 0.62

2005 0.62

1998 0.60

2003 0.58

2002 0.58

2009 0.56

2006 0.56

2007 0.55

2004 0.54

2001 0.52

• 10 of warmest years since 1998

Rate of warming accelerating

• warming of Pacific not uniform

(1988-2007)- (1950-1969)

Climate is about averages & includes variability One swallow does not a summer make Aristotle

• tropical oceans warming ~70% of global average

Projecting future climates

ScenarioIPCC-AR4 (2007)

Temperature (oC) CO2 (ppm)

B1 +1.8 (1.1-2.9) 450-500 A2 +3.4 (2.0-5.4) 750-800

NEED • high quality observations of climate and forcing factors• understanding of complex physics of global climate system• reliable modelling of climate• projecting future trajectories of greenhouse gases• “downscaling” to relevant spatial scales

“Explosion” of Uncertainties

Projected Pacific surface temperature warming

IPCC 2007

• multi-model averages• similar magnitude in short term• larger differences in magnitude in long term• the future will be WARMER

Projected Pacific rainfall changes

IPCC 2007

• more uncertainty• similar short term• wetter convergence zones (blue)• drier subtropics (orange)• ± 5% but does not mean no change (grey)

• warmer = stronger hydrological cycle• more extreme wet years• more intense droughts

Temperature 1951-1980 2035 2100Observed B1 A2 B1 A2

Tarawa 28.2 29.0-29.2 28.7-29.0 29.7-30.0 31.2-31.5Funafuti 28.0 28.5-28.8 28.5-28.8 29.3-29.5 30.8-31.0Nadi 25.6 26.1-26.4 26.1-26.4 26.9-27.1 28.4-28.6Raratonga 23.9 24.4-24.7 24.4-24.7 25.2-25.4 26.4-26.7Pitcairn 20.9 21.4-21.7 21.4-21.7 21.9-22.2 22.6-22.9

DJF rainfall 1951-1980 2035 2100Observed B1 A2 B1 A2

Tarawa 725 761-798 761-798 >870 798-870Funafuti 1,164 1,222-1,280 1,280-1,397Nadi 785 864-942Raratonga 426 447-469 469-511Pitcairn 377 339-358 339-358 302-339

Possible new climates

• low and high emissions similar in short term but larger differences in long term

• warming will continue 0.5-1.0oC warmer by 2035 and 1-1.5oC (low) to 2.5-3oC

(higher) by 2100• rainfall more uncertain but likely in

convergence zones & in subtropics• BUT warmer oceans = stronger

hydrological cycle• more extreme rainfall events• warmer air temperatures = more intense

droughts• maybe fewer TCs but those that occur

more intense• UNCLEAR how ENSO might change

Summary projected changes

SUMMARY

• future will be warmer

• some islands wetter & some drier

• more frequent and more intense extreme weather events

• importance of RATE of change

• not just new climate regime

• for foreseeable future climate will be CHANGING

Thank youWarming of the climate system is unequivocal... (IPCC 2007)

Many aspects of tropical climatic responses remain uncertain Christensen et al. (2007)

...volume of literature in refereed international journals relating to small islands and climate change since publication of the TAR is rather less than that between the Second Assessment Report in 1995 and the TAR in 2001 Mimura et al (2007)

Most of the observed increase...is very likely due to the observed increase in anthropogenic greenhouse gas concentrations” (IPCC 2007)

j.lough@aims.gov.au