El Niño to double down: Ancient plankton reveals climate clues

Extreme phenomena may appear twice as often in the near future as they do now. This is the conclusion from the study of single-celled foraminifera shells that lived on our planet about 21,000 years ago, during the last ice age. The study indicates that the climate models currently in use are accurate, significantly reinforcing concerns that El Niño will become increasingly intense.

El Niño, also known as the El Niño-Southern Oscillation (ENSO), is a recurring climate pattern related to water temperatures in the Pacific Ocean, particularly in its central and eastern tropical parts. The phenomenon is closely linked with elevated sea surface temperatures in the equatorial zone.

Warm ocean waters are low in nutrients, directly affecting fish catches. The weakening of trade winds halts the upwelling ocean current. This current typically provides cold, nutrient-rich water from ocean depths, which is replaced by warmer surface waters. The name "El Niño" is derived from the Spanish term for "child." It has a direct connection with the Christmas season when this phenomenon often intensifies. The opposite of El Niño is La Niña, during which ocean waters cool.

Research indicates that El Niño has a significant impact on the global climate because it leads to an increase in average temperatures and causes more frequent extreme weather events worldwide. Climate models employed by specialists suggest that global warming, resulting from greenhouse gas emissions, leads to greater variability in the El Niño cycle and more frequent occurrences of this phenomenon.

However, one of the major challenges for climate researchers is that precise observations of El Niño have only been conducted for several decades, and the climate models themselves are not perfect. This creates difficulties in determining the direct impact of global warming on this phenomenon. Professor Kaustubh Thirumalai of the University of Arizona and his colleagues aim to solve this problem by developing a record of changes in El Niño from 21,000 years ago, a period when the Earth's climate was much cooler than it is today. The results of this research were published in a scientific paper.

Researchers obtained climate data by analyzing the chemical composition of foraminifera shells—microscopic organisms living near the sea surface. The sea water temperature influences the chemical content of these organisms' shells, which, upon death, settle to the ocean floor, forming layers of marine sediments. These sediments provide researchers with historical data that have been found to be consistent with the results of climate models currently in use.

Confirming these models suggests an increased likelihood that El Niño will occur much more frequently in the future. This could result in more frequent occurrences of extreme weather conditions on Earth.

During the last ice age, when the climate was cooler, El Niño occurred less frequently. Scientists suggest that this phenomenon results from feedback between the winds in the Pacific Ocean and the warm water layer on its surface.

As global warming progresses, this layer becomes thinner, making it easier for winds and ocean currents to move warm water eastward and trigger intense El Niño events. Scientists predict that El Niño could occur once every 10 years rather than once every two decades, as it did in the past.