The pattern of El Nino has changed dramatically in recent years, according to the first seasonal record distinguishing different types of El Nino events over the last 400 years. A new category of El Nino has become far more prevalent in the last few decades than at any time in the past four centuries. Over the same period, traditional El Nino events have become more intense. This new finding will arguably alter our understanding of the El Nino phenomenon. Changes to El Nino will influence patterns of precipitation and temperature extremes in Australia, Southeast Asia and the Americas. Some climate model studies suggest this recent change in El Nino "flavours" could be due to climate change, but until now, long-term observations were limited. Read more: Explainer: El Nino and La Nina Our paper , published in Nature Geoscience today, fills this gap using coral records to reconstruct El Nino event types for the past 400 years. El Nino describes an almost year-long warming of the surface ocean in the tropical Pacific. These warming events are so extreme and powerful that their impacts are felt around the globe. During strong El Nino events, Australia and parts of Asia often receive much less rainfall than during normal years. The opposite applies to the western parts of the Americas, where the stronger rising motion over unusually warm ocean waters often results in heavy rainfall, causing massive floods. At the same time many of the hottest years on record across the globe coincide with El Nino events. The reason for such far-reaching influences on weather is the changes El Nino causes in atmospheric circulation. In normal years, a massive circulation cell, called the Walker circulation, moves air along the equator across the tropical Pacific. Read more: 500 years of drought and flood: trees and corals reveal Australia's climate history Warmer waters during El Nino events disrupt or even reverse this circulation pattern. The type of atmospheric disruption and the climate impacts this causes depend in particular on where the warm waters of El Nino are located. A new "flavour" of El Nino is now recognised in the tropical Pacific. This type of El Nino is characterised by warm ocean temperatures in the Central Pacific, rather than the more typical warming in the far Eastern Pacific near the South American coast, some 10,000km away. Although not as strong as the Eastern Pacific version, the Central Pacific El Nino is clearly observed in recent decades, including in 2014-15 and most recently in 2018-19. Over most of the last 400 years, El Nino events happened roughly at the same rate in the Central and Eastern Pacific. By the end of the 20th century, though, our research shows a sudden change: a sharp increase of Central Pacific El Nino events becomes evident. At the same time, the number of conventional Eastern Pacific events stayed relatively low, but the three most recent Eastern-type events (in 1982-83, 1997-98 and 2015-16) were unusually strong. Our understanding of the new Central Pacific flavour of El Nino is hindered by the fact that El Nino events happen only every 2-7 years. So during our lifetime we can observe only a handful of events. This isn't enough to really understand Central Pacific El Nino, and whether they are becoming more common. That's why we look at corals from the tropical Pacific. The corals started growing decades to centuries before we began routinely measuring the climate with instruments. The corals are an excellent archive of changes in water conditions they experience as they grow, including ocean changes related to El Nino. We combined the information from a network of coral records that preserve seasonal histories. At a seasonal timescale, we can see the characteristic patterns of past El Nino events in the chemistry of the corals. These patterns tell us which El Nino is which over the last 400 years. It is in this continuous picture of past El Ninos obtained from coral archives that we found a clear picture of an unusual recent change in the Pacific's El Nino flavours. This extraordinary change in El Nino behaviour has serious implications for societies and ecosystems around the world. For example, the most recent Eastern-Pacific El Nino event in 2015-2016 triggered disease outbreaks across the globe . With the impacts of climate change continuing to unfold, many of the hottest years on record also coincide with El Nino events. Read more: Australia moves to El Nino alert and the drought is likely to continue What's more, the Pacific Ocean is currently lingering in an El Nino state. With these confounding events, many people around the world are wondering what extreme weather will be inflicted upon them in the months and years to come. Our new record opens a door to understanding past changes of El Nino, with implications for the future too. Knowing how the different types of El Nino have unfolded in the past will mean we are better able to model, predict and plan for future El Ninos and their widespread impacts.