‘Tropical shift’ could mean fewer cyclones in region’s oceans

SEVERE storms like Tropical Cyclone Marcus which tore through Darwin in March may be becoming fewer in frequency in the region’s oceans due to the “poleward shift” of the Earth’s tropics.

New research to be published in scientific journal Nature Climate Change today, shows the number of tropical cyclones forming along Darwin’s line of latitude has been decreasing during the past 35 years.

Study co-author and University of Melbourne tropical meteorology expert professor Kevin Walsh said the southward movement of the tropics was dragging high pressure systems over Top End deserts southward, which affected the likelihood of cyclones forming.

But Professor Walsh said it was unclear from the research whether or not the number of cyclones to actually hit Darwin was also decreasing.

“The jury’s a little bit out on that at present, there’s certainly indications that that’s been occurring over the past 35 years based upon the analysis that we’re seeing here but having said that there’s a fair amount of variability by location,” he said.

“We didn’t actually look at specific locations, we’re looking at huge areas of the ocean because were trying to figure out the relationship with the very big atmospheric changes the very big ocean changes.

“What we can say is that over the larger region which is associated with large atmospheric circulations they have been decreasing in the southern hemisphere region closer to the equator.”

Prof Walsh said according to the research, the trend of the past 35 years which saw fewer cyclones forming was likely to continue.

“That’s our hypothesis because that’s kind of what the climate models are predicting for the 21st century,” he said.

But Prof Walsh said it was still too early to say whether climate change was the driving force behind the changes.

“Whether this is actually caused by climate change is a bit hard to say because the climate models at present are not projecting enough of a shift in the tropics to say whether this is caused by climate change or not,” he said.

Cyclone Marcus was the most destructive tropical storm to hit Darwin since Tracy in 1974.