Changing weather patterns

(MainsGS1:Important Geophysical phenomena such as earthquakes, Tsunami, Volcanic activity, cyclone etc.)

Context:

• A new study projects that climate change will significantly impact El Niño-La Niña weather patterns approximately by 2030.
• The study used mathematical models that analyzed sea surface temperature (SST) from 1870 to 2019 to observe ENSO and make predictions.
• The World Meteorological Organisation also predicted the first “triple dip” La Niña of the century, spread over three consecutive northern hemisphere winters.

El Niño and its impact:

• 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.
• Normally, easterly trade winds blow from the Americas towards Asia but due to El Niño , they falter and change direction to turn into westerlies, bringing warm water from the western Pacific towards the Americas.
• 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.
• Warmer water also carries tropical species towards colder areas, disrupting multiple ecosystems.
• Heat redistribution on the surface impacts airflows above the ocean as 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.

La Niña and its impact:

• La Niña, or “the girl/little girl”, is the opposite of El Niño. La Niña sees cooler than average SST in the equatorial Pacific region.
• Trade winds are stronger than usual, pushing warmer water towards Asia.
• 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 upperatmosphere — 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.

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.
• 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.

Study’s findings:

• According to the study, published in NatureCommunications journal, increased SST variability from ENSO in the eastern Equatorial Pacific (EP) will emerge around 2030 ( error margin of +/- 6 years), more than a decade earlier than that of the central Pacific ENSO. 
• If CP and EP are not separated, SST variability from ENSO will occur almost four decades earlier than previously suggested. 
• Changes in the equatorial Pacific will be visible first due to a stronger increase in EP-ENSO rainfall response, leading to increased SST variability.
• The study noted a significant increase in the amplitude of both EP-ENSO AND CP-ENSO under greenhouse warming, substantiated by strong inter-model agreement.

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 that 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 which is likely linked to a La Niña.