The growing invisible threat to airline passengers.

It seems the inflight seatbelt sign will be left on a lot more while in the air, with new research showing that clear-air turbulence is set to double by 2050, giving travellers another good reason to have a comprehensive travel insurance cover.

The research published in the journal Nature Climate Change, suggests that global warming will have a severe effect on the jet streams that pass around the planet at the same altitude as jetliners. And the bad news for travellers is that this is expected to lead to a high increase of clear-air turbulence, reports the UK's Guardian newspaper.

The study found that air turbulence will increase as much as 10 - 40 percent on flights between Europe and North America. Evidence suggests that clear-air turbulence has already increased between 40 - 90 percent on this route since 1958.

"Air turbulence does more than just interrupt the service of in-flight drinks. It injures hundreds of passengers and aircrew every year. It also causes delays and damages planes, with the total cost to society being almost $150 million each year," says Paul Williams of the University of Reading who led the research.

According to Mr Williams, most turbulence injuries occur when passengers aren't wearing their seat-belts and end up hitting their head on the aircraft ceiling. Mr Williams also admitted that the research has had an impact on his own behaviour.

"I certainly always keep my seatbelt fastened now, which I didn't used to do," he said.

Whether everybody will now choose to keep their seatbelt on for the duration of their flight is unlikely. According to the Department of Foreign Affairs and Trading, all Australians should have a comprehensive travel insurance when heading overseas to minimise the risk of unexpected events such as being injured from in flight turbulence.

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