Tropics changes mean bad news for eastern Australia
Tropical cyclones are forming further from the equator as the planet warms, bringing new regions into the zone of the intense storms including parts of eastern Australia, new research has found.
The findings are based on data from 1980-2014 analysed by Melbourne University scientists trying to understand how the expanding tropics are already affecting the development of cyclones.
‘‘In most of the ocean basins, there appears to be a decrease in tropical cyclone formation closer to the equator, accompanied by an increase in formation further away from the equator,’’ said Kevin Walsh, a professor at the university’s School of Earth Sciences, and a joint author of the paper published yesterday in Nature Climate Change.
The South Pacific is one basin where the increased southward formation and tracking is already evident, while the North Atlantic has so far seen little evidence of a shift.
‘‘With projections indicating continued tropical expansion [with climate change], these results indicate that tropical cyclone genesis will also continue to shift poleward, potentially increasing tropical cyclonerelated hazards in higher-latitude regions,’’ the paper said.
Walsh said climate models have so far had ‘‘difficulty in picking up this trend’’ now identified in the paper.
Stephen Turton, a cyclone researcher and adjunct professor at Central Queensland University, said the researchers had used ‘‘nifty’’ analysis that stripped out climate variability, such as the El Nino Southern Oscillation, to identify the poleward shift in cyclones.
The expansion of the tropics, as much as 111km a decade, had the potential to push the dry subtropics much further from the poles if greenhouse gas emissions continued to rise.
‘‘It could be Brisbane to Sydney, Rome to London, by the end of the century,’’ Professor Turton said.
He said areas such as the Gold Coast could be ‘‘a ticking time bomb’’ as cyclone tracks shifted southwards. ‘‘It’s quite alarming – policymakers need to be made aware’’ of the risks, and start considering taking adaptive steps such as tightening building codes, Turton said.
Although cyclones typically needed sea-surface temperatures of about 27 degrees, warming oceans with climate change did not necessarily increase the number of cyclones.
For instance, regions ‘‘in the deep tropics’’ close to the equator are likely to see fewer such storms as atmospheric conditions stabilise, Walsh said. That would make it harder for thunderstorms – ‘‘the seeds of cyclones’’ – to get going.
The increase in stability in those areas would come as the expected increase in rainfall transfers latent heat into the upper troposphere, decreasing the temperature differential with lower parts of the atmosphere even as the land warms.
‘‘An increase in tropical stability is one of the predictions of climate science,’’ Walsh said.
That stability, though, may be little consolation for mega-cities near the equator such as Kinshasha, the capital of the Democratic Republic of Congo, or Lagos in Nigeria, where temperature and humidity levels are expected to rise in a warming world.
Such cities ‘‘are moving into a climate regime where we can’t draw on analogues’’, Professor Turton said.
The paper did not examine how storm strength will change but Walsh said ‘‘there’s plenty of evidence to suggest the maximum intensity of cyclones is likely to increase’’ with climate change. Fairfax