ENSO
El Nino Southern Oscillation
and
La Nina

Key Info.
• It is when ocean surface temperature fluctuates
significantly from the norm
• El Nino = higher than normal, La Nina = lower;
sustained anomalies of greater than 0,5 ºC are
required
• It occurs in the eastern Pacific Ocean off the coast
of S. America
• It usually takes place around Christmas time
• The recurrence interval is 2-7 years
• ENSO is associated with floods, drought and other
disturbances; its impact can be global
• The most recent occurrence started in September
2006 and lasted until early 2007

The Walker Cell - Normal

South Pacific Gyre

El Nino Conditions

El Nino
Temperature
Anomaly

La Nina – What’s the difference?

La Nina Temperature Anomaly

Normal
El Nino
But what actually
causes these
fluctuations from the
norm?
La Nina

Impacts of El Nino
• The impact of El Nino is felt most significantly and directly
along the western coast of S. America (Peru, Ecuador); in
particular increased thunderstorm activity and heavy
rainfall leading to flooding and landslides.
• El Nino can have far reaching impacts due to
teleconnections – e.g. drier and hotter conditions over
Amazon Basin, drought in Australia and Southeast Asia,
wetter and colder winters in southern California and
northern Mexico.
• El Nino does not only affect climate, other significant
impacts include changes in sea nutrient levels as warm
nutrient poor waters flow in from the eastern Pacific
replacing the nutrient rich upwelling usually found along
the western coast of South America.
• La Nina generally leads to the opposite impacts of El Nino.

Major Episodes
• 1982-3 and 1997-8 stand out in recent
history as major El Nino events
• During the ’97-8 episode air temperature
increased by 1.5 ºC compared to the usual
increase of 0.25 ºC
• Extensive flooding took place in Peru and
Ecuador with significant impacts on life,
property and economies