BRIAN WILLIAMS THE COURIER-MAIL The Australian 26 Sep 15;
IT’S hard to imagine a more pervasive weather event than an El Nino.
This global phenomenon is a climate wildcard, fluctuating from relatively benign to a thumping drought-bearing occurrence that rattles government budgets and has emergency services stretched.
In fact, you can follow cyclic El Ninos by watching the size of Australia’s $2.3 billion wheat crop rise and fall.
El Ninos also can cause coral bleaching events on the Great Barrier Reef – part of the reason for the current decline in coral quality – and can have deadly impacts when bushfires rage across a hot and dried-out landscape.
An El Nino is a periodic warming in sea surface temperatures in the central and equatorial Pacific Ocean. La Nina, its opposite, is the cooling of those temperatures.
These changes affect weather patterns on a global scale.
Peruvian fishermen first noticed the phenomenon – El Nino is Spanish for boy-child – hundreds of years ago, with warmer water and low fish catches.
The CSIRO says that in “normal’’ years water near South America is blown west, warming as it goes. When this water reaches Australia it warms the air, making it rise and creating clouds that bring summer rain.
In an El Nino year circulation weakens and the warm water stops before it gets to Australia and we mostly end up with drought.
Large areas of Indonesia, India and Africa also have dry conditions but Peru gets floods and parts of North America warm up.
This year, with a bit of luck, Australia may dodge an El Nino bullet because its impacts here are being ameliorated by record warm temperatures in the Indian Ocean, which have been pushing moisture across the continent.
Some scientists think that El Nino conditions might be intensifying due to global warming but there is insufficient evidence for this to be conclusive.
If El Ninos are growing stronger, for whatever reason, there is plenty to be concerned about.
The US National Oceanic and Atmospheric Administration funded Benjamin Giese of the Texas A & M University to look at El Nino issues and their impacts.
One of his findings was that the 1918-19 El Nino was one of the strongest of the 20th century and that there was a possible link between it and the then flu pandemic.
That El Nino led to drought in India, which led to famine that likely contributed to about 17 million flu deaths.
A further indication of just how pervasive El Ninos are is under way in Hawaii, where University of Queensland marine biologists are studying potentially damaging effects of rapidly rising temperatures on coral reefs.
Coral bleaching and premature death is the most common effect of rising sea temperatures.
The phenomenon was observed last year when Hawaii recorded its first-ever mass bleaching event due to an unusually warm body of water in the eastern Pacific.
University of Queensland Global Change Institute director Professor Ove Hoegh-Guldberg says the combination of a strengthening El Nino and the hottest July on record means the outlook for the region’s coral is bleak.
“The coral bleaching we are uncovering in Hawaii is just the tip of the iceberg in terms of what we expect to unfold,” says Hoegh-Guldberg.
“Ocean heat has not fully dissipated since last year’s bleaching event, adding stress to corals that haven’t fully recovered and which may not be strong enough to survive another bleaching.’’
Hoegh-Guldberg also has fears for Australia’s Great Barrier Reef this summer.
The Reef is under the pump, having already lost half its coral. Because of this and extensive development, UNESCO has threatened to list the World Heritage area in danger.
Hoegh-Guldberg’s concerns are shared by Terry Hughes, a coral expert who sits on federal and state government scientific panels overseeing World Heritage area repair work.
He has warned that El Nino conditions could cause a big bleaching event like those that occurred in 1998 and 2002, subsequently setting back Reef repair work.
Weather bureau climatologist Dr Andrew Watkins says there is only one bigger weather phenomenon kicking around than the El Nino-La Nina cycle and that is climate change.
“El Nino is the main driver of variability in many parts of the world,’’ he says. “It’s the biggest driver in global temperatures.’’
The events rotate roughly on a four-yearly cycle.
Given the current El Nino is the strongest in 17 years and 17 of the 26 El Ninos since 1900 have resulted in widespread drought, that would suggest Australia faces severe drought.
But because of the extremely unusual Indian Ocean conditions, climatologists are trying to nut out a big problem: will the Indian or Pacific Ocean win out in determining weather conditions this summer?
Watkins says because the events under way are so unusual, international computer models do not have enough statistical inputs for a firm decision.
“None are really going strongly for drought,’’ Watkins says. “We hope the Indian Ocean will have a moderating influence.’’
Anyway, he points out that there has never been a year in which a cyclone did not cross the coast so, El Nino or not, someone will be flooded or suffer some sort of damage in Queensland this summer.
Although El Ninos generally reduce the number of cyclones, Watkins says a quirk is that for some reason they do not reduce the number that brew in the Gulf of Carpentaria.
This is good news for graziers in the drought-hit lower Gulf and areas stretching south into central western Queensland such as Longreach and Barcaldine in that often it takes only one good cyclone heading south from the Gulf to bring desperately needed drought-breaking rain to these areas.
