What’s the go with ENSO?

The Bureau of Meteorology recently upgraded their El Niño Watch to an El Niño Alert, meaning that there is 70%, or triple the normal likelihood of an El Niño developing in the remainder of this year. It made quite a bit of news, especially as the IPCC (Intergovernmental Panel on Climate Change) released their 1.5°C report at a similar time. Since then, however, the Royals’ visit has had everyone’s attention, and we’ve all forgotten about the looming possibility of an El Niño.

But what is El Niño and why should we care?

The El Niño Southern Oscillation (ENSO) (pronounced El Neen-yo) is one of the major global climate drivers, influencing regions that surround the Pacific Ocean. It is a system involving changes in the ocean and the atmosphere, and is one of the strongest influences on Australian year-to-year sea surface temperatures and rainfall. According to the CSIRO and the Bureau of Meteorology, El Niño and La Niña events occur every 4 to 7 years, meaning that the impacts on the climate of Australia can be seen on ten-year timescales. ENSO events are generally led by changes in the amount of heat in the tropical oceans.

ENSO has three phases: neutral, El Niño, and La Niña.

A neutral phase means there is neither an El Niño, nor a La Niña event. The trade winds that blow from East to West across the Pacific bring warm, moist air across the tropics to Australia, causing average rainfall. The waters off the coast of eastern Australia are warmer than the waters off the coast of western South America, and the temperature of the central Pacific is in between.

The neutral phase of ENSO. // Reproduced with the permission of the Bureau of Meteorology.

La Niña
A La Niña event occurs when the trade winds strengthen, forcing the pool of warmer water near Australia to be confined near the far-western tropical Pacific. This causes the temperature of the water to increase further – which helps rainclouds to form – and there is above average rainfall over eastern and northern Australia.

A typical La Niña phase. The trade winds force the warm pool more into the tropics, making it even warmer. // Reproduced with the permission of the Bureau of Meteorology.

El Niño
An El Niño event is the opposite of a La Niña; the trade winds weaken (and can sometimes reverse!), leading to warmer waters in the eastern Pacific near South America, and cooler waters near Australia. There is then lower-than-average rainfall over eastern Australia, making for dry, drought-like conditions.

A typical El Niño phase. Dry conditions in Australia are brought about through weakened trade winds. // Reproduced with the permission of the Bureau of Meteorology.

What does that mean for us?

An El Niño Alert is big news – it isn’t a guarantee of an El Niño forming, but most criteria have been ticked for one to develop. Model outlooks suggest further warming is likely – as it could affect how this summer plays out, putting questions to fire season preparedness, drought, agriculture, and health.

From the Bureau of Meteorology’s website, the effects of an El Niño can include:

  • Reduced rainfall
  • Warmer temperatures
  • Shift in temperature extremes
  • Increased frost risk
  • Reduced tropical cyclone numbers
  • Later monsoon onset
  • Increased fire danger in southeast Australia
  • Decreased alpine snow depths

This summer, we may also be affected by a positive Indian Ocean Dipole event, as well. This works in a similar way to ENSO – a positive event is where there are cool waters off the coast of western Australia, meaning less rainfall over central and eastern Australia.

When combined, the two systems can amplify each other, increasing the chances for heatwaves, droughts, and bushfire weather.

Unfortunately, this means that our drought-affected regions of NSW and QLD probably won’t get relief any time soon.

To keep an eye on what our scientists predict will happen with ENSO, go to the Bureau of Meteorology’s ENSO Outlook website.