Originally published at Scimex

The Bureau of Meteorology has declared Australia remains on an El Niño Alert. When El Niño Alert criteria have been met in the past, an El Niño event has developed around 70% of the time. The World Meteorological Organization declared El Niño nearly a month ago, reflecting differences in the metrics the two organisations use.

Organisation/s: Australian Science Media Centre

Funder: N/A

Expert Reaction

These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.

Dr Andréa Taschetto is an Associate Professor at the Climate Change Research Centre at the University of New South Wales and the ARC Centre of Excellence for Climate Extremes

“The tropical Pacific has been warming in the past couple of months with an emerging El Niño signature, but the atmosphere has been slower to respond to the ocean warming. The atmospheric pressure difference between the central and west Pacific is one of the key metrics used to monitor the coupled response between the atmosphere and ocean during El Niño events. In the past few weeks, this metric has shifted back and forth. The bureau not declaring an El Niño today means that we are still waiting for the atmosphere to respond to the ocean warming. El Niño is generally associated with below-average rainfall and increased chances of droughts and heatwaves over east/southeast Australia.”

Last updated: 01 Aug 2023 3:53pm

Declared conflicts of interest:

None declared.

Professor Janette Lindesay is a climatologist in the Fenner School of Environment & Society at The Australian National University (ANU)

“Each national weather service has its own criteria for declaring El Niño (or La Niña) events, based on key factors physically associated with the impacts of these events on weather there – particularly rainfall. The BoM uses four inter-related indicators, three of which have met El Niño thresholds. But the Southern Oscillation Index (SOI), although it has been negative in several individual recent months, has not been consistently negative to the extent required to indicate an El Niño. In 2023 this could be linked to above-average sea surface temperatures around north-eastern Australia (note current concern about Great Barrier Reef SSTs); this anomaly is likely related to ongoing ocean warming due to global heating.

Similar inconclusive behaviour of the SOI occurred in the 1930s, early and late 1940s, 1978-1981 and 1984-1986 (among others), when no El Niño event developed. It is possible that the apparently developing 2023 El Niño event may fizzle out. Whether it does or not, it remains highly likely that spring and summer temperatures will be above average across eastern and south-eastern Australia, and the scales are weighted towards a drier spring/summer than has been our recent experience. These conditions are cause for concern regarding the coming bushfire season in the east, south and south-east (which could start earlier than usual), where recent wetter years have contributed to considerable vegetation growth and a potentially dangerous fuel load in hot dry weather.”

Last updated: 01 Aug 2023 3:52pm

Declared conflicts of interest:

None declared.

Dr Milton Speer is a Visiting Fellow from the School of Mathematical and Physical Sciences at The University of Technology, Sydney

“Even though the BoM has not yet declared an El Nino it is very likely to be called in the coming weeks when the atmosphere and ocean become fully coupled. Ocean thresholds have already been reached but the atmosphere is responding only slowly. Sea-surface temperatures (SSTs) off the northwest coast of Australia have decreased to mostly neutral but they are still anomalously high in the tropics northeast of the continent. A sign of increased coupling to the atmosphere around will be if they decrease to anonymously below average in both areas around tropical Australia.

The declaration of an El Niño would mean spring and summer rainfall in eastern Australia should be mostly less than average, and in some areas, likely well below average.

Extreme maximum temperatures would likely to occur, particularly through inland northeast Australia where, clear skies would aid daytime evaporation from both the land surface and vegetation.

That will increase the bushfire danger, particularly moving through spring into summer, because of the large amount of grassland produced inland from the recent La Niña phase rainfall.

The IOD will not help with rainfall through spring because it is currently neutral with the prospect of moving to a positive phase.

It will be interesting to track the state of the Southern Annular Mode. Periods of negative SAM are conducive to dry, warm westerly winds affecting the east coast thereby leading to extreme coastal maximum temperatures. The SAM typically varies on time scales of a few weeks but has trended positive in summers during recent decades. That implies humid onshore breezes increasing the discomfort factor which is dangerous for human health.”

Last updated: 01 Aug 2023 4:01pm

Declared conflicts of interest:

None declared.