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Impossible Research Produces 400-Year El Niño Record, Revealing Startling Changes

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https://eurekalert.org/pub_releases/2019-05/uons-irp050219.php

Melbourne: Australian scientists have developed an innovative method using cores drilled from coral to produce a world first 400-year long seasonal record of El Niño events, a record that many in the field had described as impossible to extract.

The record published today in Nature Geoscience detects different types of El Niño and shows the nature of El Niño events has changed in recent decades.

This understanding of El Niño events is vital because they produce extreme weather across the globe with particularly profound effects on precipitation and temperature extremes in Australia, South East Asia and the Americas.

The 400-year record revealed a clear change in El Niño types, with an increase of Central Pacific El Niño activity in the late 20th Century and suggested future changes to the strength of Eastern Pacific El Niños.

"We are seeing more El Niños forming in the central Pacific Ocean in recent decades, which is unusual across the past 400 years," said lead author Dr Mandy Freund.

"There are even some early hints that the much stronger Eastern Pacific El Niños, like those that occurred in 1997/98 and 2015/16 may be growing in intensity."

This extraordinary result was teased out of information about past climate from coral cores spanning the Pacific Ocean, as part of Dr Freund's PhD research at the University of Melbourne and the Centre of Excellence for Climate Extremes. 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. However, until now, they had not been used to detect the different types of El Niño events.

This meant El Niño researchers were constrained by what they could say about El Niño behaviour because the instrumental record was too short and it was hard to judge whether recent decadal changes were exceptional.

"By understanding the past, we are better equipped to understand the future, especially in the context of climate change," said Dr Freund.

"Prior to this research, we did not know how frequently different types of El Niño occurred in past centuries. Now we do," said co-author from the Centre of Excellence for Climate Extremes Dr Ben Henley.

The key to unlocking the El Niño record was the understanding that coral records contained enough information to identify seasonal changes in the tropical Pacific Ocean. However, using coral records to reconstruct El Niño history at a seasonal timescale had never been done before and many people working in the field considered it impossible.

It was only after Dr Freund took her innovative approach to a team of climate scientists and coral experts: Dr Ben Henley, Prof David Karoly, Assoc Prof Helen Mcgregor, Assoc Prof Nerilie Abram, and Dr Dietmar Dommenget that they were able to proceed with the idea.

While the approach was considered challenging, leading Australian experts on past corals, Dr Mcgregor and Assoc Prof Abram, said that, while the approach might be unconventional, it was worth a shot.

After carefully refining the technique to reconstruct the signature of El Niño in space and time using new machine learning techniques, the scientists were able to compare recent coral results with the instrumental record. Dr Freund found a strong agreement between the coral cores and recorded events. This confirmation allowed the team to extend the record back in time.

Dr Freund and her team found 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.

As a result, Australian researchers have produced a world-first seasonal El Niño record extending 400 years and a new methodology that will likely be the basis for future climate research.

It took three years of hard work to achieve the result and now Dr Freund and her team are excited to see how this work can be built upon. 

"The El Niño phenomenon is one of the most important features of global climate, and changes to its behaviour have very serious implications for weather patterns and extreme events around the world," said Dr Henley.

And that centuries-long record opens a door not just to past changes but changes to El Niños in the future as well.

"This gives us an opportunity to more accurately explore how global warming may change El Niños and what this means for future weather and climate extremes," said Dr Henley.

"Having a better understanding of how different types of El Niños have affected us in the past and present, will mean we are more able to model, predict and plan for future El Niños and their wide-ranging impacts," said Dr Freund.

 

https://theconversation.com/el-nino-has-rapidly-become-stronger-and-stranger-according-to-coral-records-115560

 

The pattern of El Niño has changed dramatically in recent years, according to the first seasonal record distinguishing different types of El Niño events over the last 400 years.

A new category of El Niño 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 Niño events have become more intense. 

This new finding will arguably alter our understanding of the El Niño phenomenon. Changes to El Niño 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 Niño “flavours” could be due to climate change, but until now, long-term observations were limited. 


Read more: Explainer: El Niño and La Niña


Our paper, published in Nature Geoscience today, fills this gap using coral records to reconstruct El Niño event types for the past 400 years.

file-20190503-103057-1brkygg.png?ixlib=r Central Pacific El Niño event frequency relative to Eastern Pacific El Niño event frequency over the past four centuries, expressed as the number of events in 30-year sliding windows. Author provided

What is El Niño?

El Niño 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 Niño 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 Niño events. 

file-20190503-103071-1qbgtx3.png?ixlib=r
 
El Niño and its global impacts. Schematic of idealised atmospheric and sea surface temperature conditions during Central (top left) and Eastern Pacific events (top right). Annual global temperature anomalies (lower panel) show the familiar upward trend due to climate change. Many of the hottest years on record coincide with El Niño events. NOAA National Centers for Environmental information, Climate at a Glance: Global Time Series

The reason for such far-reaching influences on weather is the changes El Niño 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 Niño 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 Niño are located.

The new ‘flavour’ of El Niño

A new “flavour” of El Niño is now recognised in the tropical Pacific. This type of El Niño 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 Niño is clearly observed in recent decades, including in 2014-15 and most recently in 2018-19. Over most of the last 400 years, El Niño events happened roughly at the same rate in the Central and Eastern Pacific. 

Differences between Central and Eastern Pacific El Niño events and their associated drought impacts.

By the end of the 20th century, though, our research shows a sudden change: a sharp increase of Central Pacific El Niño 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.

Using coral to unlock the past

Our understanding of the new Central Pacific flavour of El Niño is hindered by the fact that El Niño 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 Niño, 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 Niño. 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 Niño events in the chemistry of the corals. These patterns tell us which El Niño is which over the last 400 years. It is in this continuous picture of past El Niños obtained from coral archives that we found a clear picture of an unusual recent change in the Pacific’s El Niño flavours.

file-20190503-103060-1uwa9b3.png?ixlib=r Underwater drilling of corals off Christmas Island (underwater team: Jennie Mallela, Oscar Branson; surface team: Jessica Hargreaves, Nerilie Abram). Jason Turl, Nerilie Abram

Why do we care?

This extraordinary change in El Niño behaviour has serious implications for societies and ecosystems around the world. For example, the most recent Eastern-Pacific El Niño 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 Niño events.


Read more: Australia moves to El Niño alert and the drought is likely to continue


What’s more, the Pacific Ocean is currently lingering in an El Niño 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 Niño, with implications for the future too. Knowing how the different types of El Niño have unfolded in the past will mean we are better able to model, predict and plan for future El Niños and their widespread impacts.

 

 

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As we see in our temp record big Nino's lead to a temporary surge in Global temps.

With us sailing so close to so many potential tipping points in our climate system we need worry each time we see a moderate ( or above?) Nino in the making.....

Once that Djin is out of the bottle there's no putting it back in!!!

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