El Niño

Context: El Niños have become stronger and their pattern too has been changing, the world’s first 400-year-long seasonal record of El Niño created by Australian scientists has revealed. Traditional El Niño events have also become more intense in nature.

What revealed this?

The El Niño trends of the past have been studied on the basis of coral cores spanning the Pacific Ocean.

It was made possible because coral cores — like tree rings — have centuries-long growth patterns and contain isotopes that can tell us a lot about the climate of the past. Hence, the key to unlocking the El Niño record was understanding that coral records contained enough information to identify seasonal changes in the tropical Pacific Ocean.

Key findings:

• The trend of El Niño in the last four centuries shows a variation in El Niño types. There has been a simultaneous increase in central Pacific events and a decrease in eastern Pacific ones since the late twentieth century.
• This leads to a ratio of central to eastern Pacific events that is unusual in a multi-century context. Compared to the past four centuries, the most recent 30-year period includes fewer, but more intense, eastern Pacific El Niño events.
• There has been an unprecedented increase in the number of El Niños forming in the central Pacific over the past 30 years, compared to all 30-year periods in the past 400 years.
• At the same time, the stronger eastern Pacific El Niños were the most intense El Niño events ever recorded, according to both, the 100-year-long instrumental record and the 400-year-long coral record.

Significance:

An understanding of El Niños in the past and present based on this four-century-old trend needs to be explored further by India for modelling, predicting and planning for future El Niños and their wide-ranging impacts.

What is ENSO?

ENSO is nothing but El Nino Southern Oscillation. As the name suggests, it is an irregular periodic variation of wind and sea surface temperature that occurs over the tropical eastern Pacific Ocean. ENSO affects the tropics (the regions surrounding the equator) and the subtropics (the regions adjacent to or bordering the tropics). The warming phase of ENSO is called El Nino, while the cooling phase is known as La Nina.

What is El Nino?

El Nino is a climatic cycle characterised by high air pressure in the Western Pacific and low air pressure in the eastern. In normal conditions, strong trade winds travel from east to west across the tropical Pacific, pushing the warm surface waters towards the western Pacific. The surface temperature could witness an increase of 8 degrees Celsius in Asian waters. At the same time, cooler waters rise up towards the surface in the eastern Pacific on the coasts of Ecuador, Peru, and Chile. This process called upwelling aids in the development of a rich ecosystem.

What causes El Nino?

El Nino sets in when there is anomaly in the pattern. The westward-blowing trade winds weaken along the Equator and due to changes in air pressure, the surface water moves eastwards to the coast of northern South America. The central and eastern Pacific regions warm up for over six months and result in an El Nino condition. The temperature of the water could rise up to 10 degrees Fahrenheit above normal. Warmer surface waters increase precipitation and bring above-normal rainfall in South America, and droughts to Indonesia and Australia.