Add bumpier transatlantic flights to the list of consequences from global warming. Clear air turbulence, the type of turbulence that comes when wind changes direction in the middle of a clear blue sky, can sneak up on a pilot.
"Turbulence is a problem not because it's uncomfortable, but it causes injuries," said researcher Paul Williams of the University of Reading in the UK. "The thing about clear air turbulence is that the pilot can't see it." So when a plane hits it, passengers and crew might not be strapped in or they may be walking about the cabin. That makes it pretty easy to suffer broken bones and even fractured skulls.
So you'd think that anything that might increase clear air turbulence would be the focus of a lot of research, right?
"I was surprised. I looked through the academic databases and I found nothing," said Williams. The reason, he said, is that it's an area of research that crosses two very different fields -- those who study climate and others who study aviation weather forecasting. Williams is one of the very few people who has a foot in both of those fields.
So Williams ran a climate model that looked at the atmosphere over the Atlantic Ocean, which currently sees about 600 flights per day. He factored in the sort of doubled carbon dioxide, warmer climate conditions that are expected in coming decades. What he looked for, in particular, were changes in the stratosphere's jet stream that could lead to more areas of turbulence.
One of the biggest signs of more turbulence is more wind shear, which is where fast-moving air is roaring right alongside a layer of slower moving air. That sort of situation creates unstable air and turbulence.
"Climate change is increasing the destabilizing influence," said Williams, whose work is published in the April 8 issue of the journal Nature Climate Change.
Long-term climate models and even daily aviation weather models can't predict the turbulence itself, but they can predict the conditions that are known to be associated with clear air turbulence, explained John Knox, a clear air turbulence forecast researcher at the University of Georgia. It's the same thing that's done in forecasting tornadoes.
"Do we actually model tornadoes in forecast models? No," said Knox. But the larger scale conditions that lead to tornadoes can be forecast. This is the approach Williams took for the clear air turbulence.
"That's the right way to do it," Knox commented.