Fewer cyclones, but bigger blows

Researchers from James Cook University in Cairns have confirmed that tropical cyclone activity in both Western Australia and Queensland is at its lowest activity for many centuries.

That’s the good news from research by postgraduate research student Jordahna Haig, published this week in the science journal Nature.

The downside is that the findings are in close agreement with several recent studies that predict that climate change will bring a reduction in the number of tropical cyclones, but an increase in their intensity.

Ms Haig’s findings are based on a study of ancient cyclone records, found in slow-growing stalagmites in limestone caves.

“Stalagmites grow up from the cave floor, as rainwater containing dissolved limestone drips down from the cave ceiling,” Ms Haig’s academic supervisor and co-author Professor Jon Nott said.

“Because tropical cyclone rainwater has a different isotope chemistry compared to other rain, we can distinguish cyclonic events in the growth layers of the stalagmites.

“By analysing the chemistry in each stalagmite layer, which is about one tenth of a millimetre thick, we can assemble records of cyclones going back 1500 to 2000 years ago.”

Working in JCU’s Centre for Tropical Sustainability Sciences, Ms Haig matched the isotope records with the Bureau of Meteorology’s relatively recent records, and generated a Cyclone Activity Index.

“The index shows that current seasonal cyclone activity is at its lowest in Western Australia since 500 AD. In Queensland, this is the quietest period since about 1400 AD.” Professor Nott said.

While that might seem like good news, these results are in close agreement with several recent studies that predict that global change will result in cyclones being less frequent but of greater intensity.

“We can’t be certain that this lull in cyclone activity is due to climate change,” Professor Nott said.

“What we can say is that our results do more than just mirror those forecasts. Our findings suggest that climate change might be influencing cyclone patterns several decades earlier than was previously predicted.”

Professor Nott said the study published in Nature this week also confirmed earlier research indicating that the last 40 to 100 years of cyclone activity in northern Australia represented a relatively quiet period in the longer-term history of cyclones in the region.

“We can see in the stalagmites that this decline began about 40 years ago,” he said.

“These results confirm that Queensland’s coastal development guidelines are based on an unrepresentative period.

“Buildings and infrastructure on low-lying coastal land in northern Queensland face a higher storm-surge risk than our planners and development authorities have allowed for.

“We would encourage planners and authorities to consider the many centuries of records we can extract from the geological record.

“This is data that should be considered very seriously as Queensland is ramping up for more coastal development with fewer safeguards.

“Certainly those proposing to build a $4.2 billion resort casino on very low-lying coastal land on the north side of Cairns would do well to consider a future in which our cyclones are more likely to be category four and five.”

For an extended article on this research on The Conversation : http://theconversation.com/au

Issued January 30, 2014

Media enquiries: E. linden . woodward@jcu.edu.au T. 07 4042 1007