Extreme El Nino events to stay

By: Harrison Hunkin, Photography by: kristianbell/RooM/Getty Images

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El Niño weather events are set to increase regardless of whether the global temperature stabilises.

A graph from the BOM depicting Australian Rainfall Deciles
Courtesy of the Bureau of Meteorology

Research published in Nature Climate Change by a team headed by CSIRO researcher Dr Guojian Wang predicts El Nino events will double by the year 2050, and continue on this path for a further century after the global mean temperature is stabilised to the Paris agreement target of 1.5°C above pre-industrial levels.

"Currently the risk of extreme El Niño events is around five events per 100 years," Wang says. "This doubles to approximately 10 events per 100 years by 2050, when our modelled emissions scenario (RCP 2.6) reaches a peak of 1.5C warming."

The models were run using the Intergovernmental Panel on Climate Change’s lowest emissions scenario (RCP2.6) which requires negative emissions late in the century.

"After this, as faster warming in the eastern equatorial Pacific persists, the risk of extreme El Niño continues upwards to about 14 events per 100 years by 2150," Wang says.

"This result is unexpected and shows that future generations will experience greater climate risks associated with extreme El Niño events than seen at 1.5°C warming."

BOM BLAST

The BoM (Bureau of Meteorology) says an El Niño occurs when sea surface temperatures in the central and eastern tropical Pacific Ocean become substantially warmer than average, and this causes a shift in atmospheric circulation.

"Typically, the equatorial trade winds blow from east to west across the Pacific Ocean," said BoM. "El Niño events are associated with a weakening, or even reversal, of the prevailing trade winds.

"Warming of ocean temperatures in the central and eastern Pacific causes this area to become more favourable for tropical rainfall and cloud development. As a result, the heavy rainfall that usually occurs to the north of Australia moves to the central and eastern parts of the Pacific basin."

 

DROUGHT MAKER

Australia’s agricultural sector suffers severely during El Niño episodes as they often lead to drier conditions that transition into drought, the body says. El Niño episodes last for a year with the greatest affects happening during winter and spring.

The El Niño event of 2002-03 is a good example of how the weather pattern can impact Australian agriculture. That El Niño brought a drought which ranks alongside the extreme droughts of 1902 and 1982-83 as one of the country’s worst in terms of severity.

A series of dry years in the southern areas intensified the effects on the entire country, the BoM says.

The extreme dryness seen during the 2002-03 El Niño mixed with record-breaking heat led to the severe bushfires in eastern NSW, Canberra and the mountains of southeast NSW and eastern Victoria. Widespread water shortages were also seen, highlighting the impact El Niño patterns can have Down Under.

 

The Southern Oscillation Index
Courtesy of the Bureau of Meteorology

RECENT EXTREMES

Centre for Southern Hemisphere Oceans research director and report co-author Dr Wenju Cai, says the three most extreme El Niño patterns have occurred in the last 35 years.

"The most severe previous extreme El Niño events occurred in 1982/83, 1997/98 and 2015/16, years associated with worldwide climate extremes," said Cai.

"Extreme El Niño events occur when the usual El Niño Pacific rainfall centre is pushed eastward toward South America, sometimes up to 16,000km, causing massive changes in the climate. The further east the centre moves, the more extreme the El Niño.

"This pulls rainfall away from Australia bringing conditions that have commonly resulted in intense droughts across the nation," Cai adds. "During such events, other countries like India, Ecuador, and China have experienced extreme events with serious socio-economic consequences."

It’s not all doom and gloom, though. While previous research suggests that extreme La Niña (opposite of El Niño) events would double under a 4.5°C warming scenario, findings indicate that under a scenario of climate stabilisation of 1.5°C warming, there would be little to no change to La Niña events, Cai says.

The research was conducted by researchers at the Hobart-based Centre for Southern Hemisphere Oceans Research, an international collaboration between the CSIRO, Qingdao National Laboratory for Marine Science and Technology, the University of New South Wales, and the University of Tasmania.

The Bureau of Meteorology routinely monitors for EL Niño episodes. Forecasts take into account the surface and sub-surface temperature patterns across the tropical Pacific Ocean, variations in trade wind strength and atmospheric pressure, and ocean currents.

The BoM also analyses the atmospheric and oceanic conditions through climate models designed for long-range seasonal outlooks. The occurrence of an El Niño requires ocean and atmospheric anomalies to come together and become self-reinforcing, it says.

For the most recent information on the likelihood of El Niño or La Niña events, visit the Bureau's ENSO Wrap-Up and ENSO tracker web pages, both updated every fortnight

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