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ENSO: El Niño & La Niña


Everything in our world is interconnected. Humans and other organisms have gotten themselves stuck in a cycle of dependency in which we rely on other plants and animals to survive on a day-to-day basis. We certainly see these relationships in the biotic world, but where do we see them in the abiotic world?


Just as organisms are dependent upon each other to survive, ocean currents are reliant upon wind patterns, temperature variations, topography, and so much more. ENSO, the El Niño-Southern Oscillation, is an example of a periodic weather phenomenon that results from shifts in the direction of wind flow and other environmental conditions. This recurring event can have a dramatic impact upon the lives of humans and animals alike in the Southern Pacific region, as will be discussed throughout this article.


 

Normal Conditions/The Neutral Phase


Most people have heard of the Coriolis Effect at some point in their lives. Whether those people actually understand it is up for debate. The Coriolis Effect is the force responsible for wind pattern variations across Earth at different latitudes. Because the Earth is spherical, wind travels faster at the equator than it does at the poles. This difference in wind speeds causes deflection of winds to the east in the Northern Hemisphere and to the west in the Southern Hemisphere.


Global ocean currents and the formation of gyers, large systems of circulating ocean currents, can be attributed to prevailing winds across Earth. Without these winds, circulation patterns that we see today would be unrecognizable and completely different than anything we’ve ever observed before.


The dominant ocean circulation pattern in the Southern Pacific region between Australia and South America favors the movement of warm ocean surface waters toward Australia. Trade winds push these warm waters from the east to the west as a result of the Coriolis Effect, causing cold waters to rise from the depths of the ocean near the South American coast, a phenomenon known as upwelling.


Upwelling can have serious ecological and economic consequences. Colder waters generally hold large quantities of dissolved oxygen because gases are more soluble at lower temperatures. As upwelling occurs, more dissolved oxygen is brought to the surface near the west coast of South America along with nutrient-rich sediment from the bottom of the ocean. These conditions are ideal for the breeding and survival of many fish species, increasing fishing industry profits and revenue from tourism during periods of normal conditions.


ENSO: El Niño-Southern Oscillations

ENSO is an irregular oceanic event that occurs irregularly every 2–7 years in the Southern Pacific Ocean between Australia and South America. This event consists of an El Niño phase, a La Niña phase, and the neutral phase discussed above.


El Niño


El Niño refers to a reversal of the direction of trade winds in the Southern Pacific Ocean due to the periodic weakening of the easterly trade winds. Winds blow from west to east instead of east to west, as they do during normal conditions. When this occurs, warm surface waters move from the west to the east toward South America instead of Australia. This has major implications on climate, precipitation levels, and coastal ecosystems of both continents.


In South America, warm ocean waters evaporate to form low pressure zones on the coast, resulting in higher average temperatures and precipitation levels. Flooding is more common in South America during El Niño, which can harm indigenous communities living in coastal areas and destroy infrastructure. Warmer waters also hold less dissolved oxygen which can cause some fish species with narrower ranges of tolerance to suffocate or migrate to new areas, upsetting the delicate balance of coastal ecosystems.


In Australia, upwelling occurs, contrary to the normal oceanic conditions in the region, and supports more aquatic species. Australian fishermen reap the benefits of El Niño as more fish migrate to the Australian coast, attracted by an abundance of rich nutrients and dissolved oxygen. However, coastal areas often experience drought in the absence of heavy rainfall that usually accompanies the neutral phase. This can have major consequences for water management and irrigation in agriculture.


La Niña


La Niña refers to the strengthening of the easterly trade winds in the Southern Pacific Ocean in the east to west direction. This weather event is extremely similar to the neutral phase, however all conditions during the neutral phase are amplified significantly. Warm ocean water is pushed forcefully in the direction of Australia, away from South America. This results in upwellings that are much larger than normal along the coast of South America, further supporting the fishing industry.


But, there are trade-offs that accompany La Niña. Although some South Americans may profit from this favorable turn in weather events, climate will shift to yield colder winters and milder summers. Plants that bloom early are more susceptible to freezing and farmers risk losing entire fields of crops to the cold, putting their annual profits on the line. Also, as discussed earlier, drought conditions present in Australia during El Niño arise in South America during La Niña.


La Niña in Australia is often associated with more intense and unforgiving monsoon seasons. Australians experience severe flooding and other natural disasters on a more frequent basis and the government must expend more money and resources on rebuilding.


Current Day

We are currently in the midst of ENSO! The Southern Pacific region is currently in an El Niño season and is expected to transition to La Niña during summer 2024. This shift from El Niño to La Niña represents a drastic change in weather patterns in the Southern Hemisphere that will impact humans and other organisms living in coastal regions of Australia and South America.


Climate Change

Flooding & Drought

As ocean temperatures rise, more evaporation occurs which creates areas of high moisture in either South America or Australia depending on what phase of ENSO the Earth is currently in. Eventually, this contributes to high levels of rainfall which often cause devastating floods. Severe flooding affects both humans and animals alike. Humans suffer from loss of infrastructure, water logging of crop fields, and millions of dollars in reconstruction. Animals suffer from loss of habitat, ecosystem instability, and bottleneck events in which a large portion of their population dies out.


On the other hand, climate change can also exacerbate drought-like conditions in cooler areas of oceanic upwelling. Wildfires, irrigation issues, and habitat loss have become more prevalent in these areas because of the one and only culprit, climate change.


A New Perspective

It’s important to keep in mind that Australia and South America are not as well equipped to handle the aftermath of large flooding or drought events as more developed countries such as the United States, Britain, and Russia. Unfortunately, these weather events happen more often in areas where developing countries are located.


Climate change is increasing the intensity in which El Niño and La Niña events occur. Each time we cycle through ENSO, the environmental consequences we observe become significantly larger in scope. As greenhouse gas emissions remain unchecked, climate change is becoming an increasingly important issue in today’s world, not only because of rising global temperatures, but because of the impacts it has on global weather patterns.


 

Recap

El Niño and La Niña are equally interesting oceanic weather phenomena that have significant effects on the environment. Although they have the potential to wreak havoc and destruction in the Southern Pacific region, there is beauty to how these events complement each other. Environmental conditions in South America during El Niño are almost identical to those in Australia during La Niña. These phenomena are just one example of the interconnectedness of different sectors of the environment.


Stay updated and active by following the Environmental Defense Initiative on Medium and our social media platforms!






Author & Editor: Emma Mazzotta


Resources

  1. Bloomberg

  2. Met Office

  3. NOAA

  4. NASA

  5. University of Washington

  6. DW

  7. SBS

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