Turbulence is a common part of flying, but severe turbulence that causes injuries, or death, is very rare.

That's why the world has reacted in shock after a man died of a heart attack and 30 others were injured when a Singapore Airlines flight from London hit severe turbulence.

The plane was cruising at 37,000 feet when the plane suddenly dropped, and passengers were flung from their seats.

As climate change causes global temperatures to rise, scientists say some of the causes of turbulence are already intensifying.

What is turbulence?

Turbulence is caused by a disruption to the air patterns a plane is travelling through.

If you think of the skies like the ocean, turbulence is similar to a wave, according to Professor Todd Lane, an atmospheric scientist at the University of Melbourne.

"Turbulence that aircraft experience is when the wind in the atmosphere changes from being horizontal to going up and down," Professor Lane explained.

"An aircraft that's flying along smoothly will start to move upwards and downwards quite radically because the wind is moving up and down."

The main causes of turbulence are mountains, storms and jet streams, which makes the task of forecasting and avoiding them straightforward in some situations.

Pilots can plan a route to avoid the air that rises over mountains, or around a storm as much as possible.

Jet streams are strong winds in the upper atmosphere where planes cruise, according to Professor Lane.

YOUTUBEThe jet stream circling the North Pole, reaching down into North America.

"Above and below the jet stream there's what's called strong wind shear, so the wind is changing speed with height quite dramatically. In those strong wind shear regions, you can get a lot of turbulence.

"So above and below these jet stream regions, there's quite a lot of what's typically called clear air turbulence, because there's no clouds involved."

It's not known at this stage what type of turbulence caused the disruption on the Singapore Airlines flight. Tracking service FlightRadar24 told Reuters there were storms — some severe — in the area at the time.

Climate change link to turbulence

As the world continues to burn fossil fuels, global temperatures are rising, and turbulence is just another natural phenomenon that's affected by that warming.

"It's affecting the wind patterns and one of those impacts that is being affected are jet streams," Professor Lane said.

"Those jet streams that are at aircraft flight levels are projected to intensify, which means that those regions will become more turbulent."

A 2017 study predicted that severe turbulence will become two to three times more common over the North Atlantic by 2050-2080 because of climate change.

However, the same study predicted a smaller increase of 50 per cent for severe turbulence over Australia.

"The nature of the jet streams are slightly different in the northern and southern hemisphere because the location of the land masses," Professor Lane said.

"There is a very strong climate change signal in the northern hemisphere, especially around the Arctic."

As well as increasingly intense jet streams, climate scientists have warned that storms are worsening as well.

Professor Lane says most of the turbulence in the tropical regions comes from thunderstorms.

"With a warmer atmosphere, the atmosphere can hold more water, which can lead to those most intense thunderstorms being more intense with climate change. As those thunderstorms become more intense, they can also generate more intense turbulence."

This isn't just a future problem, it's already happening.

Turbulence has increased

A study published last year by researchers in the UK found that climate change has already caused an increase in turbulence in the past 40 years.

"We find clear evidence of large increases around the mid-latitudes at aircraft cruising altitudes," the study from Reading University concluded.

The researchers discovered the biggest increases in clear air turbulence over the United States and the North Atlantic, also some of the world's busiest flight paths.

For any average point over the Atlantic, the research found that "severe-or-greater [clear air turbulence] increased the most, becoming 55 per cent more frequent in 2020 than 1979."

However, the research looks at instances of clear air turbulence in the atmosphere; that doesn't mean there's been the same increase in aircraft hitting that turbulence.

The modelling predicted smaller increases in turbulence in the Southern Hemisphere and over Australia.

"Following a decade of research showing that climate change will increase clear-air turbulence in the future, we now have evidence suggesting that the increase has already begun," said Professor Paul Williams, an atmospheric scientist at the University of Reading, when the study was released.

He called for more work to be done to help predict and prevent aircraft from hitting that turbulence.

"We should be investing in improved turbulence forecasting and detection systems to prevent the rougher air from translating into bumpier flights in the coming decades."