Turbulent skies: How climate change will impact flights in NZ and around the globe

www.stuff.co.nz | Georgia Forrester | Jan 29 2020

EXPLAINER: During a flight, severe turbulence can tip trolleys and throw passengers from their seats, leaving them shaken and even hurt.

And according to experts, it's something we're going to see a lot more of in the future thanks to our changing climate.

Travellers on an Emirates flight from Auckland to Dubai last year quickly realised just how bumpy a flight can get. Sudden and severe turbulence left passengers shaken - some even vomited.

The same year, passengers travelling from Vancouver to Sydney were left injured after "unforecasted and sudden turbulence" forced the plane to divert to Hawaii.

Thirty people were also injured aboard a Turkish Airlines flight from Istanbul that shook violently and plunged mid-flight before making an emergency landing.

Whether turbulence is caused by bad storms or comes out of the blue, it's something atmospheric scientists say we'll see more of. Here's why:

TYPES OF TURBULENCE

There are various kinds of turbulence that can affect aircraft, including clear-air and convective, while turbulence can also be associated with jetstreams. It can be caused by a variety of factors, including wind speed, changes in wind direction and temperature changes.

In New Zealand, some people would have felt the odd bump or two when flying past the Southern Alps. That's because downdrafts flowing off the mountains can cause turbulent mountain waves - something our pilots are well aware of.

Jetstreams are areas of very strong winds in the upper atmosphere, while clear-air turbulence is often associated with sudden changes in wind speed and direction. Convective turbulence is caused by clouds, like thunderstorms.

Weather-related turbulence is something pilots can prepare for through weather reports and intel, while radar equipment can also detect weather-associated turbulence. However, clear-air turbulence happens in clear skies and can come out of the blue.

Atmospheric scientist Paul Williams from the University of Reading says the hazardous thing about clear-air turbulence is that - unlike turbulence in clouds and storms - it doesn't show up on the cockpit radar.

"So the seatbelt sign can be off and people can be moving around inside the cabin when it strikes without warning."

Clear-air turbulence is one of the largest causes of weather-related aviation incidents. And it's this kind of turbulence that researchers say we're going to see more of as a result of our changing climate.

WHAT RESEARCHERS FOUND

A study published in Nature last year found that human-caused climate change was contributing to bumpier trans-Atlantic flights.

The study was focused on the North Atlantic jetstream - ranging between 26,000 to 49,000 feet.

It found that while the temperature difference between Earth's poles and the equator was narrowing at ground level because of climate change, the opposite was happening further up at flight cruising altitudes.

The jetstream is driven by these temperature differences, and the trend at cruising altitudes is causing an increase in turbulence-causing wind shear.

Wind shear occurs when winds change rapidly in speed or direction with height. It's one of the major causes of clear-air turbulence.

When the study was published, lead author Simon Lee said that temperatures had risen rapidly over the Arctic during the past four decades, however in the stratosphere - around 12km above the surface - they had cooled.

This had created a tug-of-war effect, where surface temperature changes acted to slow the jetstream down, while temperature changes higher up acted to speed it up.

The study showed that those opposing effects currently balanced out as the speed of the jetstream had not changed. But for the first time, this study looked at wind shear and found significant changes.

In a statement to Stuff, Williams, who was another author on the study, said that humans "have altered the climate so much that the jetstream is now 15 per cent more sheared than when satellites first began observing it".

He said at flight cruising altitudes, climate change was warming the tropical regions the fastest, because of the extra heat released when warm, moist air rises and condenses.

"The stronger north-to-south temperature difference across the jetstream is increasing the instability that generates clear-air turbulence," he said.

WHAT IT MEANS FOR TRAVEL

The study found that increasing turbulence would affect aviation in the busy trans-Atlantic flight corridor by creating a more turbulent flying environment for aircraft.

But Williams says more turbulent skies are expected to increase elsewhere.

"We do expect more turbulence in the southern latitudes around New Zealand too," he said. "But fortunately the largest increases are a bit further south over the Southern Ocean."

The University of Reading has previously calculated that the amount of severe turbulence in the atmosphere could double or triple by the period 2050-2080 if drastic action on the climate crisis is not taken.

That study, published in 2017, found strong increases in clear‐air turbulence over the entire globe, particularly the midlatitudes - where the busiest flight routes are.

That paper highlighted the importance of improving turbulence forecasts and flight planning to limit discomfort and injuries to passengers and crew.

"Unless we get better at avoiding clear-air turbulence, for example by forecasting it or detecting it from the cockpit, then a more turbulent atmosphere means the seatbelt sign being on more often, as well as more wear-and-tear on the airframe," Williams told Stuff.

"As long as the climate continues to change because of the CO2 we are putting into the atmosphere, then we expect clear-air turbulence in the jetstreams to continue to increase. We are simply going to have to get better at avoiding it."

A statement from Air New Zealand said that the airline has a dedicated team on duty 24/7 to produce flight plans and to continuously monitor conditions while aircraft are en route.

MetService data and modelling and forecasting tools are used to provide advance warning of areas affected by turbulence, icing or thunderstorms. That information is used to determine the best flight path.

If turbulence is anticipated prior to departure, the flight path will be amended, or the aircraft may carry additional fuel to allow it to avoid turbulent areas.

Once an aircraft has departed, Air NZ flight planners keep a close eye on weather updates and real-time reports from other aircraft and air traffic control. If necessary, operating crew are updated and flight paths adjusted en route to help avoid turbulence.

"Our teams follow the latest research on weather forecasting. We're keeping a close eye on how emerging technology and new forecasting systems could enhance our flight planning process," the statement read.