Sydney Morning Herald: IN SYDNEY it is rarely noticed, a silent cloud that most often steals through the city at night. Occasionally, when rain falls, a record of its passing is visible in the morning as reddy-brown splotches on the car bonnet. But fine dust from the hot dry west of the state that is sucked out to sea by vacuum cleaner-like cold fronts is much more than a nuisance for car owners. It plays an important role in climate change, and can contribute to warming and cooling of the …