The El Niño is a widely discussed phenomenon, particularly in India where it can impact the southwest monsoon. In fact, El Niño events cause serious shifts in weather patterns across the globe. While El Niño is a naturally occurring phenomenon, a key question that scientists frequently ask is: In a continuously warming planet, how will climate change affect the creation of strong El Niño events?
In a new study, researchers have found that because of climate change, extreme El Niño events are likely to become more frequent. The study was done by a team of international climate researchers led by Bin Wang of the University of Hawaii at Manoa International Pacific Research Center (IPRC). It has been published in the journal Proceedings of the National Academy of Science.
What El Niño means
El Niño is a climate phenomenon that takes place over the equatorial Pacific. It is one phase of an alternating cycle known as El Niño Southern Oscillation (ENSO). When there is a warming of the sea surface temperature in the eastern and central equatorial Pacific Ocean, it is known as El Niño. When the opposite cooling phase takes place, it is known as La Niña.
ENSO can cause extreme weather events in many regions of the world, and therefore has very important implications for seasonal climate predictions, including the monsoon in India. While El Niño causes warmer temperatures over the equatorial Pacific, these are known to suppress monsoon rainfall. When La Niña happens, it has been found to be helpful in bringing good rainfall.
The new study
The researchers examined details of 33 El Niño events from 1901 to 2017. For each event, they evaluated the onset location of the warming, its evolution and its ultimate strength. Based on such parameters, the team identified four types of El Niño, each with distinct onset and strengthening patterns.
They found a shift in El Niño behaviour since the late 1970s. All events beginning in the eastern Pacific occurred prior to that time, while all events originating in the western-central Pacific happened since then. The researchers suggested, therefore, that climate change effects have shifted the El Niño onset location from the eastern Pacific to the western Pacific, and caused more frequent extreme El Niño events.
What the findings imply
The team focused on the factors that seemed to be controlling these shifts, including increased surface temperatures in the western Pacific warm pool, and easterly winds in the central Pacific. They found that with continued global warming, those factors may lead to a continued increase in frequency in extreme El Niño events.
“Simulations with global climate models suggest that if the observed background changes continue under future anthropogenic forcing, more frequent extreme El Niño events will induce profound socioeconomic consequences,” Wang said in a statement released by his university.
The classification system in this study provides a tool for climate modelling of El Niño and La Niña. The university said the team plans to explore further how this work may help improve predictions of future El Niño events.