After three soggy years in a row of La Nina, Australia has endured record floods with the Kimberley in Western Australia and north and central Queensland the latest regions to be inundated.
Although the rains were a relief after the heat, drought and fires that came before, they have long outstayed their welcome.
The latest update from the Bureau of Meteorology points to a continuing weakening of La Nina – but points to the possibility of El Nino emerging by the autumn.
You can think of El Nino as being the opposite of La Nina.
La Nina is known for bringing cooler, rainy weather, while El Nino brings hot, dry conditions. This means it’s often associated with drought, heatwaves and bushfires.
The world’s hottest year on record in 2016 was an El Nino year.
Let’s take a closer look at BoM’s forecast and what Australians can expect in the coming months.
The difference between El Nino, La Nina and climate change
La Nina and El Nino events are “climate drivers”, which means they are part of the natural oscillations of the Earth’s climate.
Human-caused climate change, on the other hand, acts over a longer term, steadily bringing up the planet’s average temperature and exacerbating some of the impacts of these events.
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La Nina is characterised by cooler waters than normal in the tropical eastern Pacific near Peru and Ecuador and warmer waters in the west Pacific, including around northern Australia.
When we have La Nina we have an increased chance of wet conditions over northern and eastern Australia, especially in spring. The past three years with consecutive La Nina events have followed this pattern.
In contrast, El Nino is associated with warmer waters over the central and eastern Pacific Ocean and cooler waters in the west. These conditions bring an increased chance of warmer and drier conditions in Australia.
For now we have a dissipating La Nina, and there is strong confidence it will continue to weaken over the coming weeks. We expect it to be properly finished by the end of summer.
The likelihood of El Nino forming
As we look further ahead, our confidence in what will happen next reduces.
BoM’s outlook suggests El Nino conditions could arrive by late autumn, but other forecast models point to a lower chance of one emerging at all.
Forecasts of El Nino are challenging several months in advance, but particularly at this time of year when they have to overcome the “autumn predictability barrier”.
In autumn, there is less variation in the Pacific Ocean’s temperature and it’s harder to forecast if an El Nino or La Nina will emerge by winter.
We are by no means guaranteed a switch to El Nino, but there is a higher probability of one forming in the next few months than we’ve seen for several years.
Australia is also affected by other natural climate drivers, such as the Indian Ocean Dipole, which has a strong effect on winter weather.
This climate driver is brought about by interactions between ocean currents and the atmosphere, and influences rainfall patterns around the Indian Ocean, including Australia.
It’s currently forecast to move into a “positive phase” by early winter, which would favour a drier winter over most of Australia as well, but this is also still uncertain.
From floods to drought?
With indications of a shift to El Nino and positive Indian Ocean Dipole, should we expect to swing from floods to drought?
Drought occurs on different time scales, but Australia’s most devastating droughts, which result in major agricultural losses and water restrictions, require several years of dry conditions.
With our dams full, it’s unlikely we’ll see a major drought for a while. If we have an extended period without La Nina or negative Indian Ocean Dipole conditions, then drought may start to appear again.
However, the drier weather would also raise the risks of other hazards such as heatwaves and bushfires.
The horror 2019-20 fire season came off the back of a weak El Niño and a strongly positive Indian Ocean Dipole. Indeed, Australia’s hottest summer on record was during the El Niño of 2018-19.
This time, our three consecutive La Nina events have resulted in more vegetation growth. This means next summer, there will be more fuel for fires to burn.
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New heights for global temperatures
El Nino doesn’t just affect Australia.
For example, during El Nino events we typically see a weaker Indian monsoon and drier conditions over southern Africa.
East Africa, which has suffered greatly from drought in recent times, is usually wetter during El Nino.
As these events involve the warming of a large area of the Pacific Ocean, they tend to raise the global average surface temperature by about one-tenth of a degree. That might not sound like very much, but it could push the global average surface temperature to record highs, particularly in the year after an El Nino forms.
Given the planet is rapidly warming due to our continuing high greenhouse gas emissions, and the fact we haven’t had a big El Nino for a while, even a moderate El Nino could mean the world experiences a new record hot year.
There is even the possibility the global average temperature could surpass 1.5 degrees Celsius above pre-industrial levels for the first time.
Although we’re aiming to keep global warming under 1.5 degrees to meet the Paris Agreement, an individual year above this mark does not mean we have failed. Still, it’s not a good sign if we start to hit that mark.
Is climate change altering El Nino?
It’s not yet clear exactly how climate change may be altering El Nino.
However, there are indications climate change may be moving El Nino events towards the central Pacific nearer the international dateline.
Climate change could also possibly strengthen rainfall responses to El Nino and La Nina over the Pacific and elsewhere.
This may worsen both our floods and droughts in Australia, but more research is needed.
Unfortunately, in terms of global temperatures and Australian heatwaves, it’s clear the combination of human-caused climate change and a major El Nino event increases the likelihood of record-breaking events.
An El Nino may not be a welcome reprieve from the past few soggy years.
Andrew King is senior lecturer in climate science at The University of Melbourne.
This article is republished from The Conversation under a Creative Commons licence. Read the original article.
