Global Warming: EL NIÑO

& LA NIÑA

Dr. Manish Semwal

Niño“Christ Child” “The Boy” “The Little One” Cf: La Niña “The Girl”

:2009/10 El Nino

Base period: 1971-2000, Data source: NCEP, EMC

Anomalous SST (Jan-Mar 2010)

NINO4 region NINO3 region

Tahiti

Darwin

• Mean pressure is lower at Darwin than Tahiti• The term “Southern Oscillation” was also coined by Gilbert Walker• The SOI measures the strength of the Pacific Walker circulation

The Southern Oscillation Index

x

• Thus, “EL NIÑO” is a condition in the central and eastern equatorial Pacific Ocean where unusual warming is occurring. (Note that the formation/development of El Niño is very far from the country.. )Then, why is it affecting the philippines..

The phenomenon is called SOUTHERN OSCILLATION…

What is El Niño

• Warming of sea surface waters in the central and eastern tropical Pacific Ocean.

• El Niño: the ocean part: Warm phase of ENSO:

El Niño - Southern Oscillation• Southern Oscillation: the atmospheric part;

a global wave pattern• La Niña: is the cold phase of ENSO:

Cool sea temperatures in tropical Pacific

• EN events occur about every 3-7 years

During El Niño Episode During La Niña Episode 

·  

Drier weather conditions Wetter weather conditions

Initial results of diagnostic and statistical studies on general influences of ENSO on Philippine climate

Weak monsoon activity

Weak tropical cyclones activity

Below normal rainfall

Above normal air temperatures

- occurrence of isolated heavy rainfall in short duration

- delayed onset of the rainy season- early termination of the rainy season

- tropical cyclones follow tracks further off the Philippines

- less number of tropical cyclones entering the Philippine Area of Responsibility (PAR)

Above normal rainfallNear-to-below normal air temperatures

Moderate to Strong tropical cyclones activity

Moderate to strong monsoon activity

- increased cloudiness and widespread rains

- near normal cyclone tracks (near and/or crossing the country)

- near normal to early onset of the rainy season

- near-to-above normal cyclone occurrences in the PAR- rain-effective cyclones

Top: normal Bottom: El Niño condition

Open University, 1998

Normal

El Nino

Eastern boundary

•Shallow thermocline•Cold, nutrient-rich water•Mixing depth shallower than critical depth•High NPP

•Deep thermocline •Warm, nutrient-poor water•Mixing depth not as much shallower than critical depth•Lower NPP

El Niño La Niña

Equatorial upwelling

Much weaker Much stronger

California Current upwelling

Weaker Stronger

California Current temperature

Warmer Cooler

California Current thermocline

Deeper Shallower

West Pacific warm pool

Spreads east across equator

Compressed in western Pacific

Region Period ImpactIndonesia Life of event Drier

Northeast Brazil March-May DrierCentral America

/MexicoMay-October Drier

West Coast South America

March-May Wetter

Central South America

June-December Wetter

Southeast Africa December-February Drier

Understand EL Nino & La Nina

Rainfall in thunderstorms and organized convection gives rise to latent heat release in the atmosphere, which determines atmospheric heating patterns.

The heating patterns set up low level convergence and upper level divergence that drives Rossby waves in the atmosphere.

These propagate to other regions (teleconnections) and determine the atmospheric circulation locally.

Different flavors of El NiñoEvents come in different “flavors”

El Niño refers to a warming of the tropical Pacific but this doesnot take account of surrounding areas and character of event.

Tropical winds and rainfallrespond to total SSTs andso depend on time of yearand details. Surface windconvergence is in vicinityof warmest water, notanomaly.

Small changes in SST canchange region of warmestwater by 1000 km or more!

El Niño and Global warming

1998 warmest year on record, 2001 second warmestEl Niño contributes to global warming

There is a pattern of more and bigger El Niños in past 20 years

El Niño years

La Niña years

Is global warming contributing to changes in El Niño?Likely, yes, to some extent.Which part is natural variability?

Global warming

Heating

Temperature & Evaporation

water holding capacity

atmospheric moisture

greenhouse effect & rain intensity

Droughts & Flood

How will El Niño events change with global warming?

El Niño involves a build up and depletion of heat as well as major redistribution of heat in the ocean and the atmosphere during the course of events.• Because GHGs trap heat, they interfere.• Possibly expand the Pacific Warm Pool.• Enhance rate of recharge of heat losses.• More warming at surface: enhanced thermocline enhanced swings• More frequent El Niños?• Some models more El Niño-like with increased GHGs.• But models do not simulate El Niño well• Nor do they agreeThe hydrological cycle is expected to speed up with increased GHGs. Increased evaporation enhances the moisture content of the atmosphere which makes more moisture available for rainfall. ENSO-related droughts are apt to be more severe and last longer, while floods are likely to be enhanced.

Main effects of climate oscillations on pelagic species

• Changes in temperature/nutrients affect primary production and food web

• Higher trophic levels affected by changes in food availability

• Changes in temperature affect rates of growth/survival

• Fish/nekton with limited temperature range can move to water of preferred temperature, leading to range shifts

Central Case: Rising Temperatures and Seas May Take the Maldives Under

• 80% of this island nation’s land is <1 m above water.• Globally warming temperatures are causing sea levels

to rise worldwide, endangering many island nations.• The 2004 tsunami (tidal wave) hit the Maldives hard.

Some Reading

Bibliography

• http://www.realclimate.org/index.php/archives/2006/05/el-nino-global-warming/

• http://www.aurumscience.com/environmental/8_climatechange/lecture.html

• http://www.ucmp.berkeley.edu/education/dynamic/session4/sess4_hydroatmo3.htm