The Canberra fires of 2003: a pine planataion on the edge of the Brindebella Ranges ignites
Credit: SMH
The fires of 2003, and the ones that struck the Eyre Peninsula of South Australia in January 2005, where nine people died and some 800 km2 of bush was incinerated - were not totally unexpected; much of Australia is hot and dry, and the continent has been like this for millennia.
But Australia may be becoming even hotter and drier and, by all historical comparisons, the intensity of the recent fires is epic. A deep drought has continued for the past decade. Dams serving the city of Canberra and nearby areas have been as low as 35 per cent full. Canberra has recovered steadily since the fire of 2003, but every Australian knows the risk of devastating fires each summer remains high.
A number of climate experts have begun to ask whether the current drought and the recent fire seasons, which have been considered exceptional, are actually the new commonplace.
Answering that question requires consideration of familiar global atmospheric phenomena. The weather system known as El Niño, for instance, has had major effects on Australia's climate for thousands of years. The effects of global warming, atmospheric pollution, and water shortages - for which humanity may bear substantial responsibility - must also be factored in. And even if climatologists can sort out the causes of Australia's suffering, can anything be done to reverse their effects? The answers are not necessarily encouraging.
Conditions in Australia today seem unlike anything on record. Early written accounts, archaeological data, tree rings, cores of ocean sediments, and other indicators are all beginning to paint a picture of the history and prehistory of Australia's climate.
According to David A. Jones, a climatologist at the Bureau of Meteorology in Melbourne, Australia's climate is rapidly warming, and the warming trend is compounding the drought. Another climatologist, Timothy P. Barnett of the Scripps Institution of Oceanography in San Diego, California, agrees. He points out that the centre of Australia - what Australians love to call the 'red centre' - appears to be getting hotter and drier more quickly than the edges of the continent. Such preferential heating, he says, is evidence of a prolonged, permanent climate shift.
And it's not just Australia. Droughts are becoming distressingly common across many of the world's less-watered regions. New research shows that the percentage of the Earth's land area undergoing serious drought has doubled in the past 30 years, according to data presented at a meeting of the American Meteorological Society in January 2005. Aiguo Dai and his colleagues of the U.S. National Centre for Atmospheric Research in Boulder, Colorado, said that almost half the change is due to rising temperatures rather than decreases in rainfall or snowfall. "Global climate models predict increased drying over most land areas during their warm season, as carbon dioxide and other greenhouse gases increase," Dai told reporters. "Our analyses suggest that this drying may have already begun."
Climate experts at the U.S. National Oceanic and Atmospheric Administration envision such a preponderance of prolonged, severe, geographically wide-ranging events in the future that they have coined the term 'mega-drought' to describe them.
From his studies of historical climate patterns recorded in tree rings, Thomas W. Swetnam of the University of Arizona in Tucson - a former firefighter with the U.S. Forest Service - sees a clear link between the worst droughts and the worst fire years. And there are good reasons to think that El Niño, a big factor in Australia's droughts, is becoming more powerful.
For three or four years out of five, on average, ocean temperatures stray very little from their mean. But in that fifth year - the interval itself is a rough one - the sea surface and atmosphere in the tropical regions of the western Pacific Ocean warm dramatically. The warm water and air masses move eastward across the equatorial region, until they reach the west coast of the Americas.
Because it arrives around Christmas, the warm currents and air masses are known as El Niño, literally 'the [Christ] child'. El Niños usually last between one and two years, and cause wet conditions off Peru and in the U.S. southwest. In Australia, an El Niño causes drought, as high-pressure cells, or air masses, develop over the northern half of Australia and create persistent warm, dry conditions.
After an interval of three to seven years, an opposite phenomenon, dubbed La Niña, 'the girl', takes hold, which lasts a similar length of time to El Niño. In La Niña years, Australia becomes wetter.
The cycling between the two extremes encourages the evolution of fire-dominated ecosystems. In wet years, grasses, trees and other vegetation grow abundantly, producing large amounts of fuel to burn during dry periods. The ashes from the fires serve as fertiliser for a new round of explosive growth during the next wet phase.
