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More unpredictable effects of climate change


 
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Dr Neville Nicholls, from Monash University’s School of Geography and Environmental Science, has a long interest in drought and looks at our abilities to predict them and their causes.     
The term El Nino was known by scientists for a long term before the media spotlight began to glow some years ago. Dr Nicholls published a paper in 1973 that linked drought in Papua New Guinea to the El Nino phenomenon and, although received quietly it was later used in the late 1980s by geographers at the Australian National University to predict rainfall. This allows international aid into the country when it is clear that there will be a long drought like the one in 1997.

Strangely it was known in the 1920s and 1930s that El Nino may well be linked to droughts in Australia but the scientific community lost interest. It wasn’t until the late 1970s that Dr Nicholls, using the early research, together with the ongoing records of drought for Australia, confirmed this link could be used to predict drought in Australia. He eventually convinced the Bureau of Meteorology to introduce a seasonal forecast service which still operates today. One of the difficulties for current El Nino predictions is that climate change is altering the relationships that are used to make the forecasts, so the predictions are less accurate than they once were.

El Nino is the main cause of droughts in Australia, Indonesia, New Guinea and parts of China and Africa, as well as being the cause of very heavy rain in parts of South America. El Nino is also responsible for a reduction in tropical cyclones in northern Australia and can be used to forecast cyclone activity. For Australia, El Nino has been the major cause of drought and causes those droughts to be different to those in Europe and North America. The strong droughts tend to be a year long, usually starting in April or May and peaking in December. They are also very wide spread, so if there is drought in Victoria there will often be drought in Queensland.

 
This strong patterning has its effect on native flora and fauna who have adapted to live under the conditions of drought and flooding rains.    
Many of our birds, for instance, do not breed on an annual cycle but will breed quickly when the La Nina rains come.
Breeding in red kangaroos happens the same way, a clear adaptation to the El Nino and La Nina effects. This has been happening for thousands of years, as have the El Nino cycles.
Red kangaroo image from Allan Fox

 
One of the current problems with drought is the effects of humans on the climate. Last year was the thirteenth in a row that Melbourne received below average rainfall. In 150 years of record keeping the longest previous stretch of dry years was six years in a row, so the new record has more than doubled that stretch. This dryness is mirrored from Perth to the east coast and is a sign that something other than El Nino is taking effect. Perth, in fact, has had below average rainfall for over 30 years, something that wouldn’t happen under the El Nino cycles.

Indeed, the storm tracks for the atmospheric lows have shifted south over the last few decades, something that was expected to happen under increased greenhouse emissions. Though not completely proven, there is a concern that the baseline has shifted more or less permanently and that less rain will mark the future. Unfortunately there are no models currently capable of predicting how global warming will affect El Nino and La Nina but it is certain that there will be some effects of having temperatures rise. El Nino and La Nina will most likely still operate but if there are longer dry periods caused by global warming then El Nino will continue to make matters worse.

It is ironic that, just as we have the means to make predictions about drought and rainfall, we interfere with those predictions by causing global warming. That is certainly a drought on our thinking.

Text: V.B. June 2010

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