La Niña

The term La Niña typically refers to atmospheric as well as oceanic patterns, as with El Niño. It often lasts longer than El Niño, sometimes persisting or recurring for two or more years. The term El Niño/Southern Oscillation, or ENSO, refers to the combination of atmospheric and oceanic effects associated with both El Niño and La Niña. As counterpart to El Niño, La Niña is defined as cooler-than-normal sea-surface temperatures (SST) in the central and eastern tropical parts of the Pacific Ocean.  

What is the difference between La Niña and El Niño?

El Niño and La Niña are extreme phases of a naturally occurring climate cycle. Both terms refer to large-scale changes in SST across the eastern tropical Pacific. When sea surface temperatures are near normal, the phase is termed ‘neutral’. To qualify as an El Niño event, according to the US National Oceanic and Atmospheric Administration (NOAA), SSTs must remain at or above 0.5°C (about 1°F) for at least three months . For La Niña, the SSTs are below average rather than above. In part, because La Niña more closely resembles the neutral state of the Pacific, it is somewhat easier for a La Niña event to last longer (up to 2–3 years) than an El Niño, which rarely persists for more than a year at a time.

How do El Niño and La Niña occur?

El Niño and La Niña events are natural occurrences in the global climate system resulting from variations in ocean temperatures in the Equatorial Pacific. In turn, changes in the atmosphere impact the ocean temperatures and currents. The system oscillates between warm (El Niño) to neutral or cold (La Niña) conditions.

How often do El Niño and La Niña occur?

El Niño and La Niña occur on average every 3 to 5 years. However, in the historical record the interval between events has varied from 2 to 7 years.

Does a La Niña always follow an El Niño?

A La Niña episode may, but does not always, follow El Niño.

How do we predict El Niño/La Niña?

The first model-based ENSO predictions started in the late 1980s. Today, a number of computer models around the world use current ocean temperatures and atmospheric conditions to project the state of ENSO, looking a year or more into the future. Forecasters examine multi-model ensembles, scrutinizing where these models agree or disagree in order to issue El Niño and La Niña forecasts. Among the leading sources of regular ENSO forecasts are NOAA’s Climate Prediction Center, the International Research Institute for Climate and Society at Columbia University (working with NOAA), and the Australian Bureau of Meteorology. (Note that the Australian BOM uses a higher threshold for El Niño development than the US definition; see above).

The World Meteorological Organization (WMO) facilitates development of a consensus-based El Niño/La Niña Update that is issued on a quasi-regular basis (approximately once every three months) through a collaborative effort with the International Research Institute for Climate and Society (IRI) and based on contributions from all the leading centres around the world. 

Key forecasts
WMO
NOAA 
Australia BOM
IRI

Generally, the strongest ENSO events are predicted more accurately than weaker ones. A 2012 analysis in the Bulletin of the American Meteorological Society evaluated ENSO forecasts from 20 different prediction models for the period 2002 to 2011. The study found that the predictive skill of these models actually declined in the 2000s as compared to the 1980s and 1990s—not because of any loss in model quality (the models themselves had actually improved), but because the weaker, more variable ENSO events during this period made forecasting a far greater challenge.

What is the relationship between El Niño/La Niña and global warming?

The jury is still out on this. Are we likely to see more El Niño’s because of global warming? If so, will they be more intense? These are the main research questions facing the science community today. So far, there is no evidence suggesting that climate change is increasing the frequency of El Niño and La Niña events. However, it is likely to increase the impacts, especially of El Niño, in terms of more intense heat, drought, and heavier precipitation. Further research will help separate the natural climate variability from any trends due to human activities.

What are the global impacts of La Niña?

While El Niño and La Niña do impact global climate patterns; however, they neither affect all regions nor do are their impacts in a given region the same. In many locations, especially in the tropics, La Niña (or cold episodes) produces roughly the opposite climate variations from El Niño. For instance, parts of Australia and Indonesia are prone to drought during El Niño but are typically wetter than normal during La Niña. For the most accurate information at national or local level, it is important to consult National Meteorological and Hydrological Services. WMO Regional Climate Centres may also provide more particular information at national and regional levels.

The impacts of each La Niña event are never exactly the same. They depend on the intensity of the event, the time of year when it develops and the interaction with other climate patterns. La Niña is often associated with wet conditions in eastern Australia, and with heavy rainfall in Indonesia, the Philippines and Thailand. La Niña usually leads to increased rainfall in North Eastern Brazil, Colombia and other northern parts of South America and is associated with rainfall deficiency in Uruguay and parts of Argentina. Drier-than-normal conditions are generally observed along coastal Ecuador and North Western Peru. La Niña episodes feature a very wave-like jet stream flow over the United States and Canada in the northern winter, with colder and stormier than average conditions across the North, and warmer and less stormy conditions across the South. La Niña events are generally associated with increased rainfall in southern Africa, although they are not the only contributing factors. La Niña is associated with rainfall deficiency in equatorial eastern Africa – for instance Somalia and eastern Kenya.

It is important to stress that such factors as the Indian Ocean Dipole, the North Atlantic Oscillation/Arctic Oscillation can also have an important influence on seasonal climate.