Global Warming: EL NIÑO & LA NIÑA Dr. Manish Semwal Niño“Christ Child” “The Boy” “The Little One” Cf: La Niña “The Girl”

NINO4 region NINO3 region :2009/10 El Nino Anomalous SST (Jan-Mar 2010) Base period: 1971-2000, Data source: NCEP, EMC

The Southern Oscillation Index Darwin Tahiti 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 phenomenon is called SOUTHERN OSCILLATION… 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..

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

Initial results of diagnostic and statistical studies on general influences of ENSO on Philippine climate During El Niño Episode During La Niña Episode   ·               Weak monsoon activity   Moderate to strong monsoon activity - delayed onset of the rainy season - early termination of the rainy season - increased cloudiness and widespread rains - occurrence of isolated heavy rainfall in short duration - near normal to early onset of the rainy season Weak tropical cyclones activity Moderate to Strong tropical cyclones activity - tropical cyclones follow tracks further off the Philippines - near normal cyclone tracks (near and/or crossing the country) - less number of tropical cyclones entering the Philippine Area of Responsibility (PAR) - near-to-above normal cyclone occurrences in the PAR - rain-effective cyclones Below normal rainfall Above normal rainfall Above normal air temperatures Near-to-below normal air temperatures Drier weather conditions Wetter weather conditions

Top: normal Bottom: El Niño condition 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 Normal El Nino Open University, 1998

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

Central America /Mexico Region Period Impact Indonesia Life of event Drier Northeast Brazil March-May Central America /Mexico May-October West Coast South America Wetter Central South America June-December Southeast Africa December-February

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 Niño Events come in different “flavors” El Niño refers to a warming of the tropical Pacific but this does not take account of surrounding areas and character of event. Tropical winds and rainfall respond to total SSTs and so depend on time of year and details. Surface wind convergence is in vicinity of warmest water, not anomaly. Small changes in SST can change region of warmest water by 1000 km or more!

El Niño and Global warming 1998 warmest year on record, 2001 second warmest El 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 agree The 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