Just weeks after the worst bushfires in the Australian state of New South Wales in more than a decade, research shows climate change could exacerbate a natural climate phenomena that triggers drought and fires in southern Australia.
Climate in much of Australia is at the mercy of swings in ocean temperature and wind patterns in the tropics, including the El Nino-Southern Oscillation pattern. Cooling of the waters in the western Pacific can trigger drought in parts of Australia and Indonesia. The reverse, La Nina, warms waters in the western Pacific, often triggering heavy rains in parts of Australia.
Another phenomenon, the Indian Ocean Dipole, also triggers a drying out of the weather in southern Australia around spring time, priming large areas for bushfires. The worry is that climate change will exacerbate swings in the Indian Ocean Dipole and threaten more lives and property.
“Over the past 50 years, the dipole has been trending upwards, increasing the number of positive events, occurring an unprecedented 11 times over the past 30 years,” said the study’s lead author Wenju Cai, of Australia’s state-funded Commonwealth Scientific and Industrial Research Organisation’s Wealth from Ocean Flagship.
“For example, there were three consecutive positive dipole events between 2006 and 2008, which preconditioned the catastrophic Black Saturday bushfires in Victoria,” Cai said in a statement.
He was referring to the February 2009 fires around the city of Melbourne that killed more than 170 people in the nation’s deadliest natural disaster. The fires occurred during a record-breaking heatwave.
The study, published in the journal Nature Geoscience on Friday, shows that extreme weather events in Australia such as drought and bushfires are linked to temperature changes in the Indian Ocean.
The Indian Ocean Dipole has been known for some time and farmers are issued with regular updates to allow them to plan crop planting. But Cai’s study shows the dipole frequency is trending upwards and rising temperatures and drought could worsen its impact over time. And not just in Australia.
The dipole influences weather events across the Indian Ocean and fluctuates between ‘positive’, ‘neutral’ and ‘negative’ phases approximately every three to eight years.
During a positive phase, higher-than-average sea-surface temperatures and more rain occur in the western Indian Ocean region. In the east, waters are cooler and the weather becomes drier. This tends to cause droughts in East Asia and Australia but flooding in parts of the Indian subcontinent and East Africa.
Positive dipole activity has, to date, preconditioned major wildfires in southeast Australia, caused coral reef death across western Sumatra, and exacerbated malaria outbreaks in East Africa, scientists say.
Cai’s study underscores how natural cycles play a critical role in the global climate but that loading up the atmosphere with extra greenhouse gases can intensify these natural processes. Scientists are still learning just how global warming can interfere with these natural cycles.
The good news is that the dipole’s impact can be largely predicted four to six months ahead.
“Our major bushfires in summer have been linked with a positive dipole in winter and spring, and therefore the dipole offers a way of predicting summer bushfire conditions. This research enables us to better anticipate drought and increased bushfire risk,” Cai said.
The bad news it may only get worse for Australia.
“In future climate, a decline in spring rainfall and a rise in temperature induced by a dipole event, exacerbated by a long-term drying trend in a warming climate, will greatly increase the risk of major bushfires,” Cai wrote in a commentary in The Conversation news site in Australia.
“The implications are, of course, far broader than Australia. The dipole has, to date, preconditioned wildfires in Indonesia, caused coral reef death across western Sumatra, and exacerbated malaria outbreaks in East Africa. We expect these extreme events to become more intense in the future,” he said.
David Fogarty is a former Reuters correspondent and writes on climate change and the environment. He is a specialist media consultant based in Singapore. You can follow David on Twitter: @FogartyClimate, or contact him at Falling Apples Consultancy.