Nervous flyers are easily triggered by turbulence, and despite its apparent harmlessness, this up-on-air phenomenon can get quite scary. Although turbulence often manifests as minor instances of innocuous bumping, it can also be the cause of structural damage or injuries for passengers.

As we ramble on through the planet's warmest season yet, scientists may have found a correlation between increased heat levels and turbulence that is worth reading. 

A study published in Geophysical Research Letters in June details the finding that clear-air turbulence (CAT) has shown a rising prevalence across the globe from 1979 to 2020.

According to the World Meteorological Organization, CAT refers to medium or high-level atmospheric turbulence that occurs in areas with significant wind shear. 

The term "clear air" indicates that this turbulence typically happens without the presence of clouds, and it can become challenging as it is difficult to visually detect.

The analysis, authored by researchers from the University of Reading, revealed this significant increases in CAT are projected to intensify in response to higher heat levels in our climate.

"Our study represents the best evidence yet that CAT has increased over the past four decades, consistent with the expected effects of climate change.” wrote the authors.

The study shows moderate turbulence has been rising from 70.0 to 96.1 hours, and light turbulence, reaching 546.8 hours compared to the previous 466.5 hours.

“At a typical point over the North Atlantic — one of the world’s busiest flight routes — the total annual duration of severe turbulence increased by 55% from 17.7 hours in 1979 to 27.4 hours in 2020,” read the report.

Mark Prosser, doctoral researcher in the Department of Meteorology and one of the paper's co-authors, talked to NBC6 in an exclusive interview, and said this finding only confirms the expected trends predicted in previous work by researcher Luke N. Storer back in 2017.

"[The study] found that climate models indicated that clear-air turbulence could double/triple in the midlatitudes by the period 2050-2080 (compared with the pre-industrial period) if we keep on emitting large amount of greenhouse gases (CO2, methane etc)” he said.

Prosser reflected on the fact 2020 is decades away from the study’s predicted period of increased CAT levels, and how “[it is] interesting to know (as demonstrated by our study) that some of this increase has already manifested”.

Turbulence as a consequence of heat

The definition of turbulence entails this phenomena as a series of chaotic and unpredictable eddies of air, disrupted from a calmer state by diverse forces.

According to a report by the National Weather Service, turbulence can be classified into three levels: light, moderate and severe. 

Light turbulence causes momentary slight changes in altitude with mild bumpiness, and moderate turbulence is similar but more intense. 

Severe turbulence, on the other hand, causes large and abrupt changes in altitude and attitude, and could potentially lead to momentary loss of control of the aircraft, causing considerable discomfort and potential injuries.

The report also stressed that turbulence can be attributed to two main sources: mechanical and thermal.

Whilst mechanical turbulence is caused by the roughness of surfaces, thermal turbulence arises from surface heating when heat convection currents rise from the surface and blend with the air flowing over it.

Turbulence spans throughout the entire convection layer, reaching from its base to the top. Unstable atmospheric conditions and gusty winds are generated due to heating from beneath, resulting in bumpy and challenging flying conditions.

Charlie Bible, a retired Delta pilot, provided some insight on the relationship between heat and turbulence levels in an interview with NBC6.

“The air is like water; once it is messed up it may cause the airplane to move 100 or even 200 miles. When flying below 50,000 feet, the heat in direction of the land become less smooth, and this creates more bumpiness” 

Bible also stresses it is inevitable that there will be more turbulence in correlation to an increase in hot temperatures. 

"You are going to have more turbulence in summertime than in wintertime. So, if the Earth's atmosphere is increasing in temperature, then there will be more turbulence in consequence and more bouncing around,” he concluded.

But as far as severe turbulence, Bible says he has only seen this with thunderstorms or similar extreme circumstances.

"I've never had any major upsets with turbulence. Severe turbulence where [the aircraft] becomes uncontrollable; I've only heard of a couple of instances where the plane has lost control." 

So, what exactly is the cost of CAT and what those this scientific finding entail?

What is the cost of turbulence, really?

According to a report by the National Center for Atmospheric Research Applications Laboratory. about 65,000 flights encounter moderate turbulence every year, and about 5,500 encounter severe turbulence.

The report also notes that despite the fact not every significant encounter with turbulence results in an injury, turbulence still accounts for approximately 75% of all weather-related accidents and incidents, and it can result in significant expenses for airlines due to damage and disruptions.

“First of all, It's important to say that we're not forecasting apocalyptically bumpy skies nor are we expecting 'commercial' planes to crash or people within them to die, but, many of us are likely to encounter turbulence more often when we do fly,” Prosser explained.

"The statistic that was used (which may now be slightly out of date) is a current cost of $150-500 million to the aviation industry in the US alone attributable to turbulence encounters." he added, referencing a figure on the NCAR report.

“Needless to say this figure is likely to rise if the trends we've seen over the last 40 years continue,” he added.

But, aside from the monetary cost, there is also the human cost, Prosser demands. 

As per the findings of a publication in the National Center for Atmospheric Research, a review of NTSB data from 1992 to 2001 evidenced turbulence was a factor in at least 509 accidents in the United States that resulted in 251 deaths in general aviation. 

“Between 2002 and 2013, there were 430 passenger and crew injuries due to turbulence,” reads the publication.

How to manage it?

So, should the aviation industry see this findings as a warning to mitigate the situation? Prosser says yes.

“They need to be cognisant of this trend and factor it in to their investments/plans going forward. It's probably unwise to wait until the turbulence forces changes before adapting,” he said.

Well apart from humanities large scale project of reducing our global carbon foot print, Prosser insists that focusing on improving our forecasting ability and increased use of seat belts at cruise level altitude are only “some of the things we can do”.

“There's a promising technology called LIDAR that could potentially detect CAT with a few seconds lead time (works by firing a beam of light out in front of the plane and having that beam reflected back giving information about whether the air immediately ahead is turbulent),” he detailed.

“A few seconds time might give passengers time to get strapped in, which would greatly reduce their chances of injury in the case of a severe turbulence encounter.” he added.

What to expect?

Prosser explained that "bumpier skies do not automatically mean bumpier journeys", because the latter depends on how good the aviation industry constructively progresses in bettering their prediction of where and when patches of turbulence will occur and for how long. 

“If we become really good at short term prediction, then pilots can skillfully avoid them. If our prediction ability stalls or is slower than the increasing trend in turbulence then bumpier skies will mean bumpier flights.” finalized Prosser.