Australians should prepare for a summer of heatwaves even if an El Niño does not take hold this year, a senior climate scientist at the Bureau of Meteorology has said.
Dr Karl Braganza, the bureau’s national manager for climate services, said this year “could be significant in terms of heatwaves and fires”, but was unlikely to repeat the horrors of the 2019-20 black summer bushfires.
He said the current record breaking heat in the world’s oceans could be one reason behind the failure of El Niño to form so far.
“Historically we have not seen a situation like this before going into an El Niño event with record global ocean temperatures,” he said.
El Niño is characterised by high ocean temperatures in the equatorial Pacific that weaken the east to west trade winds that blow over the ocean. This climate pattern can drive droughts and heat in Australia, and can push up global temperatures.
While the World Meteorological Organization and the US National Oceanic and Atmospheric Administration have already said an El Niño is in place, the bureau said this week the atmosphere was still not giving a consistent signal – mainly the changes in the trade winds – that were typical of an El Nińo.
According to the bureau’s latest long range outlook, released on Thursday, most of the country is likely to see warmer than average temperatures out to October, and lower than average rainfall.
Braganza said that forecast stood, regardless of whether an El Niño did develop. He said if El Niño was declared, it would give the bureau more confidence that beyond October the outlook would remain mostly warm and dry throughout the rest of the summer.
Looking at El Niños of the past, Braganza said typically you would see a tongue of warm ocean water extending from the west coast of central America across the equatorial Pacific.
This would usually have a horseshoe-shaped area of cooler water surrounding it off Australia’s northeast that sets up a reversal of the trade winds, locking the El Niño in place.
“This does not look like that canonical El Niño,” said Braganza. “The western Pacific and the Indian Ocean are quite warm and the tropical Atlantic is extremely warm at the moment.”
Differences in temperature across different parts of the ocean can drive large scale weather patterns like El Niño, but right now it was warm across most of the ocean.
Braganza said it was a “point of conjecture” that these widespread record ocean temperatures “could be making it harder for the El Niño to get going in the atmosphere”.
“The bottom line is that we are adding heat to the ocean and that has to be modulating the ocean’s natural variability to some degree, but we don’t have a clear scientific understanding of that at the moment.”
Braganza said as the world’s climate had been changed, the ability to forecast based on past events had been compromised.
The bureau still considers there to be a 70% chance of an El Niño developing later this year.
Braganza said forecasts were also showing that another phenomenon in the Indian Ocean that can reduce rainfall was likely to develop over spring. If that happens and an El Niño also locks into place “we will likely strengthen our forecast advice”, Braganza said.
Some climate scientists and bushfire experts have expressed concern that after three consecutive years of very wet La Niña summers, there is now a lot of grass and vegetation that could become fuel for fires.
“The fuel growth is remarkable and in our new climate system, how quickly can we dry out that fuel?” Braganza said.
“You would say it won’t be like a 2019 event, but our message is to prepare for a summer where it could be significant in terms of heatwaves and fires. But I’m less worried than I would be if we had had two years of drought.”
And Braganza said meteorologists were also watching closely for any climate impacts from a significant loss of Antarctic sea ice this year compared with previous years.
Less sea ice had the potential to contribute to changes in wind and weather patterns, he said.
“What we are seeing now due to the lack of growth is that instead of sea ice extending into the mid-latitudes, you now have dark ocean. That changes the solar radiation balance in the southern hemisphere.”
