El Niño and La Niña are parts of a climate cycle known as the El Niño-Southern Oscillation (ENSO). This cycle involves changes in the temperature of surface waters in the tropical Pacific Ocean, which in turn impact atmospheric pressure and wind patterns worldwide. Though part of the same cycle, El Niño and La Niña represent different phases of ENSO and result in distinct changes in global weather patterns.
El Niño
El Niño results in unusually warm ocean surface temperatures in the central and eastern tropical Pacific Ocean. The name is Spanish for “the boy child” because the event typically occurs around Christmas. El Niño generally causes high air pressure in the western Pacific and low air pressure in the eastern Pacific.
La Niña
La Niña, Spanish for “the girl child”, is the flip side of El Niño. Older names for this side of the cycle were anti-El Niño and El Viejo, which means “the old man.” La Niña features unusually cold ocean surface temperatures in the central and eastern tropical Pacific Ocean. It typically results in high air pressure in the eastern Pacific and low air pressure in the western Pacific.
How do El Niño and La Niña Work?
The mechanisms behind El Niño and La Niña are complex, involving interactions between the ocean and the atmosphere.
During normal (non-ENSO) conditions, steady westward trade winds drive warm surface waters towards the western Pacific, piling it up in the vicinity of Indonesia. The resulting vacuum pulls up colder, nutrient-rich water from the ocean depths that replace the warm surface water in the eastern Pacific. This process is known as upwelling.
During El Niño, the westward trade winds weaken or even reverse. This reduces the upwelling so that warm water flows back towards the east. The warm water essentially suppresses the upwelling of cold, nutrient-rich water.
During La Niña, the trade winds are stronger than normal. This intensifies the normal upwelling of colder water in the eastern Pacific, leading to even cooler than normal surface temperatures.
Frequency and Effects on Global Weather Patterns
El Niño and La Niña events occur irregularly, approximately every 2-7 years, and last anywhere from 9 months to 2 years.
El Niño events often produce warmer winters in the northern United States and cooler, wetter winters in the southern U.S. They frequently cause drier conditions in the western Pacific and increased rainfall in the eastern Pacific.
Conversely, La Niña typically produces colder winters in the northern U.S., warmer, drier winters in the south, wetter conditions in the western Pacific, and drier conditions in the eastern Pacific.
Effects of El Niño and La Niña
Because both El Niño and La Niña have substantial effects on global weather patterns, they impact the lives of people around the world.
Economic Impact
ENSO events have profound economic implications. In particular, they effect agriculture, fisheries, energy, and other weather-dependent industries.
During El Niño, fisheries off the coast of Peru and Ecuador sometimes collapse due to the suppression of nutrient-rich cold water upwelling. Increased precipitation leads to floods in some regions, while others suffer from drought conditions. These events impact agriculture and cause food price fluctuations.
La Niña has the opposite effect, such as a surge in fish populations due to increased nutrients in upwelling water and potential agricultural losses in areas that experience drought.
Ecological Impact
The ecological impacts of ENSO events are equally significant.
For instance, El Niño events reduce primary productivity in the ocean due to a lack of nutrients, affecting the entire food chain, from phytoplankton to top predators. Global coral bleaching events can occur. On land, increased rainfall leads to plant disease outbreaks or provides conditions for invasive species to thrive.
La Niña leads to increased marine productivity due to intensified upwelling but also exacerbates wildfires on land in regions experiencing drought.
Health and Social Impact
ENSO events impacts human health and society.
El Niño, through its influence on weather patterns, contributes to disease outbreaks, particularly vector-borne diseases like malaria or dengue fever, which increase with warmer temperatures and increased rainfall.
Meanwhile, both El Niño and La Niña can disrupt livelihoods, leading to food insecurity and displacement due to extreme weather events like floods and droughts. Sometimes these effects lead to civil conflicts.
Are El Niño and La Niña Linked to Global Warming?
There is ongoing scientific debate regarding the impact of global warming on the El Niño-Southern Oscillation (ENSO) cycle, which includes El Niño and La Niña events.
Some climate models predict that global warming could lead to more frequent and more intense El Niño events because of increased heat in the Pacific Ocean. Other models suggest that while the frequency of El Niño events may not increase, the intensity of individual events could increase, leading to more severe weather disruptions when El Niño does occur.
As for La Niña, it’s also unclear how global warming might impact these events. Some models suggest that warming could make La Niña events more frequent or intense, while others predict that warming might reduce the occurrence of La Niña events.
A key challenge in predicting how global warming affects ENSO is the complexity of the system. The ENSO cycle involves intricate interactions between the ocean and the atmosphere, and many factors come into play. These include wind patterns, ocean currents, and temperature gradients.
Also, it’s important to note that the relationship might not be one-way. While global warming could influence the ENSO cycle, changes in the ENSO cycle can also impact global climate patterns and potentially influence the rate of global warming.
References
- Changnon, Stanley A (2000). El Niño 1997-98 The Climate Event of The Century. New York: Oxford University Press. ISBN 0-19-513552-0.
- Druffel, Ellen R. M.; Griffin, Sheila; Vetter, Desiree; Dunbar, Robert B.; Mucciarone, David M. (2015). “Identification of frequent La Niña events during the early 1800s in the east equatorial Pacific”. Geophysical Research Letters. 42 (5): 1512–1519. doi:10.1002/2014GL062997
- L’Heureux, M.; Collins, D.; Hu, Z.-Z. (2012). “Linear trends in sea surface temperature of the tropical Pacific Ocean and implications for the El Niño-Southern Oscillation”. Climate Dynamics. 40 (5–6): 1–14. doi:10.1007/s00382-012-1331-2
- Power, Scott; Haylock, Malcolm; Colman, Rob; Wang, Xiangdong (2006). “The Predictability of Interdecadal Changes in ENSO Activity and ENSO Teleconnections”. Journal of Climate. 19 (19): 4755–4771. doi:10.1175/JCLI3868.1
- Trenberth, Kevin E. (1997). “The Definition of El Niño”. Bulletin of the American Meteorological Society. 78 (12): 2771–2777. doi:10.1175/1520-0477(1997)078<2771:TDOENO>2.0.CO;2