EL-NINO AND LA-NINA - GEOGRAPHY
News: Explained | El Niño, La Niña and changing weather patterns
What's in the news?
● A
new study projects that climate change will significantly impact El Niño-La
Niña weather patterns approximately by 2030 - a decade before what was earlier
predicted, and around four decades earlier than the suggested timeline without
separating the two regimes.
● This is predicted to result in further global climate disruptions.
Key takeaways:
● El Niño and La Niña are
atmospheric patterns that influence warming and cooling of sea surface
temperatures in the Central and Equatorial Pacific.
● The
two opposing patterns occur in an irregular cycle called the El Niño Southern
Oscillation (ENSO) cycle.
● The study used mathematical models that analyzed sea surface temperature (SST) from 1870 to 2019 to observe ENSO and make predictions.
El Nino:
● El
Niño is a loose translation of “little boy” or even “Christ child” in Spanish.
South American fishermen are believed to have noticed unusually warm water in
the Pacific Ocean in the 1600s. Earlier, it was also called “El Niño de
Navidad,” since it peaks around December.
● El
Niño is the warming of sea waters in the
Central-east Equatorial Pacific that occurs every few years.
● During
El Niño, surface temperatures in the equatorial Pacific rise, and trade winds
(east-west winds) that blow near the Equator - weaken.
● Change in wind direction:
○ Normally,
easterly trade winds blow from the Americas towards Asia.
○ Due
to El Niño, they falter and change direction to turn into westerlies, bringing
warm water from the western Pacific towards the Americas.
● Ceasing of upwelling:
○ Deeper
waters are usually more nutrient-rich, but upwelling (where deeper waters rise
towards the surface) is reduced under El Niño, in turn reducing phytoplankton
off the coast.
○ Fish
that eat phytoplankton are affected, followed by other organisms higher up the
food chain.
○ Warmer
water also carries tropical species towards colder areas, disrupting multiple
ecosystems.
● Heat redistribution on
the surface impacts airflows above the ocean. While easterly winds are dry and
steady, Pacific westerlies are warmer and moistureier.
● Since
the Pacific covers almost one-third of the earth, changes in its temperature
and subsequent alteration of wind patterns disrupt global weather patterns.
● Impacts:
○ El
Niño causes dry, warm winters in
Northern U.S. and Canada and increased flooding risk on the U.S. gulf coast and
southeastern U.S.
○ It also brings drought to Indonesia and Australia.
La Niña:
● La
Niña, or “the girl/little girl”, is the opposite of El Niño.
● La Niña is cooler than average
SST in the equatorial Pacific region.
● Trade
winds are stronger than usual, pushing warmer water towards Asia.
● Increased Upwelling:
○ On
the American west coast, upwelling increases, bringing nutrient-rich water to
the surface.
● Pacific
cold waters close to the Americas push jet streams - narrow bands of strong
winds in the upper atmosphere - northwards.
● This
leads to drier conditions in the Southern U.S., and heavy rainfall in the
northwest and Canada.
● La
Niña also makes winter temperatures warmer in the south and cooler to the north
of the U.S.
● Impacts:
○ La Niña has also been
associated with heavy floods in Australia.
○ Two
successive La Niña events in the last two years caused intense flooding in
Australia, resulting in significant damage.
○ Parts of Australia are battling floods this year for the third year in a row, even as scientists hope La Niña will be relatively shorter in 2022.
El Niño Southern Oscillation:
● The
combination of El Niño, La Niña, and the neutral state between the two opposite
effects is called the El Niño Southern Oscillation (ENSO).
● Southern
oscillations are large-scale changes in
sea level pressure in the tropical Pacific region.
● Discovery:
○ The
phenomenon was discovered by Sir Gilbert
Walker, who was researching the drought in India in the early 20th century
and found an alternating variation in pressure between the eastern and western
Pacific Ocean.
○ He
found that when pressure was high at Darwin,
Australia (western Pacific) it was low at Tahiti
(eastern Pacific), and vice-versa.
○ However, it was only in the late 1960s that Norwegian meteorologist Jacob Bjerknes and others convincingly linked this with El Niño.
Impact on India’s monsoons:
● In
India, El Niño causes weak rainfall and
more heat, while La Niña intensifies rainfall across South Asia,
particularly in India’s northwest and Bangladesh during the monsoon.
● At
present, India too is witnessing an extended triple dip La Niña. As reported by
The Hindu, this, in part, is why India saw surplus rain in September, a month
that usually sees the monsoon retreat, for the third year in a row.
● While
an IMD forecast indicated that Central India and the southern peninsula would
get 6% more than their historical average this year, rainfall far exceeded this
- likely linked to a La Niña.