Why hasn’t Australia declared El Niño despite its expected arrival?

An El Niño event results in an increased chance for dry weather, particularly on the eastern side of Australia. Credit: Shutterstock/ArliftAtoz2205

The world experienced its hottest week ever recorded two weeks ago. Simultaneously, the United Nations’ weather agency officially declared a global El Niño event.

Following the UN’s declaration, both the World Meteorological Organization and the U.S. Government weather agency confirmed the occurrence of the climate event. However, the Australian Bureau of Meteorology has yet to release a statement confirming El Niño.

In explaining the discrepancy in declarations, Associate Professor Andrea Taschetto, a climate scientist from UNSW Science’s Climate Change Research Center, discusses the significance of El Niño for Australia, the different manifestations it can take, and why its official confirmation is still pending.

“After three years of wet La Niña cycles, it appears that we are heading towards a strong El Niño event,” says A/Prof Taschetto. “However, confirming an El Niño event requires consistent measurements of various metrics, which the Australian Bureau of Meteorology is currently monitoring.”

What is El Niño?

Taschetto: El Niño is defined as a warm condition in the tropical Pacific. The El Niño Southern Oscillation (ENSO) is a recurring cycle in the tropical Pacific that occurs every three to seven years. The warm phase of this cycle is called El Niño, while the cool phase is known as La Niña.

What causes El Niño?

Under normal conditions, trade winds blow from South America to Australia in the equatorial Pacific, resulting in warm water accumulation around Australia and cold water upwelling near South America.

During an El Niño event, the east-to-west trade winds weaken, causing less water to be pushed towards Australia and reduced upwelling of cold water near South America. Consequently, the central and eastern Pacific experience more significant warming than usual.

How do these ocean changes impact the atmosphere?

Significantly, changes in the ocean influence the atmosphere, creating a positive feedback loop. When sea surface temperatures in the central and eastern tropical Pacific Ocean become substantially warmer than average, it triggers a shift in atmospheric circulation.

The region of cloud development, thunderstorms, and rainfall associated with Northern Australia moves eastward to the central Pacific, resulting in drier conditions in Australia.

How will an El Niño episode impact Australia?

An El Niño event increases the likelihood of dry weather and below-average rainfall, leading to an increased frequency of droughts, especially in the eastern half of Australia, spanning from the Northern Territory to Victoria and Tasmania.

Additionally, reduced cloud cover during El Niño increases the chance of frost, but the main characteristic of this climate event is the deficit in rainfall.

How does El Niño affect other regions globally?

El Niño causes a shift in the Walker Circulation, the vertical movement of air along the equatorial Pacific, resulting in warm air rising over the Indonesian Seas and descending over the east Pacific. This change in circulation can trigger atmospheric waves that travel towards the poles and impact other global regions. For example, it can affect sea ice cover in Antarctica.

El Niño also affects South America, bringing increased rainfall to countries close to the warming waters such as Ecuador and Peru, while regions like Northeast Brazil experience dry conditions with reduced rainfall.

Is every El Niño event the same?

In the early 2000s, scientists discovered that El Niño can manifest in different ways. Strong El Niño events exhibit maximum warming on the eastern side of the tropical Pacific near South America, but these events may not have the most significant impact on the Australian climate. On the other hand, “moderate” El Niño events, also known as El Niño Modoki events, appear to have a greater effect on Australian rainfall.

Why hasn’t the Bureau of Meteorology declared El Niño yet?

The discrepancies in declaring ENSO events among forecasting agencies stem from the monitoring of various metrics, including subsurface water temperatures and cloud cover in the western Pacific Ocean.

The Australian Bureau of Meteorology (BOM) has not yet declared El Niño because one of the crucial metrics, the difference in atmospheric pressure between Tahiti and Darwin, has not exhibited the expected behavior of a classic El Niño. This pressure difference, which is linked to the weakening of trade winds, is a key indicator of an El Niño event and must persist for weeks before a confirmation can be made.

What is the connection between El Niño and climate change?

ENSO is a natural phenomenon in our climate system and is not directly related to the extreme weather changes observed in the past century due to climate change. ENSO has always occurred and will continue to do so. However, its future manifestations may be slightly different due to background warming.

Several studies suggest that extreme El Niño and La Niña events may become more frequent in the future due to increasing greenhouse gas concentrations.

Provided by
University of New South Wales

If El Niño is expected, why hasn’t it yet been declared in Australia? (2023, July 18)
retrieved 18 July 2023
from https://phys.org/news/2023-07-el-nio-hasnt-declared-australia.html

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