Air turbulence is a serious subject, and it might surprise you to know that turbulence is the leading cause of injuries to passengers and flight attendants. It costs U.S. airlines nearly $500 million a year in medical costs, injuries, delays, and physical damage.

The number of turbulence incidents is increasing, and scientists attribute this to global warming and climate change. We’re talking about CAT — or clear air turbulence — which cockpit instruments can’t detect.

Some of the most turbulent routes in the world? Between Chile and Bolivia, Milan and Geneva, and one short flight between two cities in Kazakhstan.

But remember, severe turbulence can happen on any route. So when the captain turns off the seatbelt sign, do the smart thing, be a contrarian, and keep it fastened.