CO2 rise ‘to bring multiple droughts’

A CLIMATE phenomenon in the Indian Ocean linked with dry periods in Australia could nearly triple in frequency, a new paper suggests.

A CLIMATE phenomenon in the Indian Ocean linked with dry periods in Australia, including the drought that helped spark the Black Saturday bushfires of 2009, could nearly triple in frequency under a scenario of CO2-induced climate change, a new paper suggests.

In a study published today in Nature, CSIRO marine and atmospheric science researcher Wenju Cai says extreme Indian Ocean Dipole positive phases, linked to dry weather in Australia, will increase from once every 17.3 years over the 20th century to once every 6.3 years in the 21st century.

Like its cousin El Nino-La Nina pattern in the Pacific Ocean, the Indian Ocean Dipole influences climate over thousands of kilometres.

During a positive phase IOD subsurface sea temperatures around Sumatra cool as strengthening easterly winds push the warm surface water across the ocean towards eastern tropical Africa.

Around the cooler ocean convection is lessened, leading to a decrease in rainfall. Drought and bushfires often follow.

In the paper, Dr Cai says increased atmospheric CO2 leads to stronger easterly winds along the Indian Ocean equator.

Dr Cai said the Black Saturday fires had followed an unprecedented three consecutive positive IOD events in 2006, 2007 and 2008, which had a “cumulative impact’’.

“South-eastern Australia was in drought from 2000 to 2010 and that coincided with a high frequency of positive IODs, taking away the rain and causing the conditions to be more susceptible to be severe,’’ he said.