Are El Niño-La Niña weather patterns changing?

What are the adverse effects of these recurring climate changes? What is the El Niño Southern Oscillation? How have these phenomena affected Indian monsoons?

The story so far:

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. This is bound to result in further global climate disruptions.

What is the El Niño phenomenon?

El Niño is the warming of sea water 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. Due to El Niño, they falter and change direction to turn into westerlies, bringing warm water from the western Pacific towards the Americas. The phenomena of upwelling, where nutrient-rich waters rise towards the surface, is reduced under El Niño. This in turn reduces phytoplankton. Thus, fish that eat phytoplankton are affected, followed by other organisms higher up the food chain. Warm waters also carry tropical species towards colder areas, disrupting multiple ecosystems. Since the Pacific covers almost one-third of the earth, changes in its temperature and subsequent alteration of wind patterns disrupt global weather patterns. El Niño causes dry, warm winter in Northern U.S. and Canada and increases the risk of flooding in the U.S. gulf coast and southeastern U.S. It also brings drought to Indonesia and Australia.

What is La Niña?

La Niña is the opposite of El Niño. La Niña sees cooler than average sea surface temperature (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 upper atmosphere — northwards. This leads to drier conditions in Southern U.S., and heavy rainfall in Canada.

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.

What were the study’s findings?

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.

ENSO’s scale is significant enough to influence global climate. According to the study, published in the Nature Communications 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 (CP) 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 the EP-ENSO rainfall response, leading to increased SST variability.

What is the effect 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, like the rest of the globe, 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.

THE GIST

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.

El Niño is the warming of sea waters in the central-east Equatorial Pacific that occurs every few years. La Niña is the opposite, wherein we see cooler than average sea surface temperature in the equatorial Pacific region. The neutral state between the two opposite effects is called the El Niño Southern Oscillation.

In India, El Niño causes weak rainfall and more heat, while La Niña intensifies rainfall across South Asia.