EIGHT years of drought, and record temperatures that have baked outback soils dry, were blamed for yesterday' s dust storm that turned Sydney's sky red, and the sun blue.
Scientists estimated 75,000 tonnes of dust were being blown across NSW every hour in what may have been the most severe dust storm Sydney has seen since the droughts of the 1940s.
NSW, said John Leys, a scientist with the Department of Environment and Climate Change, was now experiencing "something like 10 times more dust storms than normal".
''In the last two months we have been getting a major dust storm once a week,'' said the scientist who helps manage DustWatch, which has a network of 32 monitoring stations across the state. ''We have been getting more and more of them [dust storms] over the last seven years.''
Dr Leys was reluctant to say it was the result of climate change. But he noted, ''we are getting the hottest summers we have ever had. We have had droughts for eight years.''
On average, Wentworth, in south-western NSW, had 270 millimetres of rain a year. ''Since 2001 only one year has achieved that,'' said Dr Leys, adding that in the past eight years the town had run up a 400mm ''rainfall deficit''.
Barry Hanstrum, the weather bureau's NSW regional director, said rain during the past six months over the border region covering far north-west NSW, north-east South Australia and south-west Queensland was in the lowest 10 per cent on record.
With soil so dry, said Mr Hanstrum, whenever strong winds blew ''you would have a dust storm, any time''.
Stephen Cattle, a University of Sydney soil scientist, estimated yesterday's dust storm stripped several millimetres of top soil from hundreds of square kilometres of NSW farms. ''This will reduce the productivity of their soil, certainly,'' said Dr Cattle, adding that the top layer was where most of the soil's valuable organic matter was stored.
Yesterday's dust storm was the third in a week to rise from the salt lakes of South Australia, that include Lake Eyre and Lake Frome.
The first, last week, blew dust over Hobart and towards New Zealand. A second, whipped up on Monday, sent a long plume of dust billowing over NSW and Canberra on Tuesday, before heading out over the Tasman.
Sydney's dust cloud stemmed from the third storm, triggered on Tuesday over the South Australian salt lakes. It was fuelled by gales of 90 to 100km/h that howled into western NSW. Aircraft reported seeing dust 2500 metres high.
Yesterday morning, Mr Hanstrum said, the cloud covered from ''Nowra to Dubbo and Orange, and up to Moree''. By midday fresh satellite imagery showed dust stretching from the Victorian border, north to Goondiwindi and Bundaberg.
Mr Hanstrum said Sydney airport visibility had been reduced to 400 metres. ''We have to go back to the 1940 when we had visibility as low'' because of dust. At Whitecliffs on Tuesday visibility fell to 20 metres.
Scientists are already studying telltale red dust that fell over New Zealand's snowfields last week.
Nigel Tapper, a Monash University atmosphere scientist, said dust kicked up over the Lake Eyre basin on September 12 had crossed the Tasman on September 14 and fallen near Mount Hutt, New Zealand.
''You could see the redness on the alpine snow,'' Professor Tapper said. By studying the dust's mineral composition they hope to confirm its origin.
The scientists also hope to identify any micro-organisms in the dust that could provide clues to how dust storms may transport agricultural diseases from continent to continent.
Professor Tapper said Chinese dust storms had reached North America, while nutrients in African dust storms helped feed the Amazon forests of South America.
Weather bureau records show big dust storms swept over Sydney in 1994, 1968, 1957, and 1942. While scientists are still calculating the total mass of yesterday's occurrence, another that swept eastern Australia on October 23, 2002, carried somewhere between 3.35 million to 4.85 million tonnes of dust.
Email a friend