After the Singapore Airlines plane encountered turbulence, there have been many articles claiming that serious turbulence incidents are increasing rapidly due to global warming. The articles below in the Seattle Times and on the BBC are just two of hundreds of such stories
Based on a study by investigators at the University of Reading, some rather specific stories suggest that turbulence has increased by 55% in 50 years.
Is this right? As I will describe below, there are significant problems with apocalyptic claims about a much bumpier sky.
But before we discuss these turbulence claims, remember that aircraft turbulence can be caused by a number of different mechanisms, and not all of them are related to climate change.
Much of the turbulence is due to convection associated with large cumulus clouds, such as cumulus clouds, that create thunderstorms. Turbulence on the Singapore Airlines flight was related to tropical convection.
Other disturbances are associated with high-amplitude atmospheric waves associated with mountains (see figure). Such chaos is often observed downstream of major mountain ranges such as the Rockies and Sierra Nevada.
Source: Whiteman (2000)
There is also turbulence associated with vertical wind shear: if wind speed changes rapidly with altitude, the atmosphere can break up into turbulent eddies. This type of turbulence usually occurs without clouds and is therefore often called fresh air turbulence and is generally the least severe primary disturbance mechanism. Finally, there may be turbulence near the surface, called mechanical disturbancee, when air moves around an object.
How do the frequencies of disturbance sources differ? The best records and observations are found in the United States and the contributions of different types of turbulence by month are shown below (from FAA documents) for 2009-2018.
Convective turbulence is number one and dominates during spring and summer. Fresh air or shear turbulence is number two and most dominant during the cool season.
Is the chaos increasing rapidly over time as media headlines suggest?
So where do all these dramatic claims about increasing unrest with global warming come from?
In this article, they DO NOT USE ANY WEEKLY OBSERVATIONS. Instead, they used gridded analysis of weather data (called reanalysis) and used a theoretical model that they proposed would show turbulence due to shear. But they don’t really have the data to back this up or to prove their approach is reliable.
To make matters even more confusing, the 55% increase in chaos they quote is NOT for the entire world but only for an area in the North Atlantic. If you read the actual article (I did), there are all kinds of standards that never made it into the media stories.
To get some perspective, their 55% increase in this one location represents an increase from 17.7 to 27.4 hours PER YEAR. An additional ten hours a year is 0.0011 of a year. For the least severe source of aircraft turbulence (vertical wind shear).
The media didn’t tell you that the increase was so small. Still worried? And that paper says nothing about other sources of strong turbulence, which are overall more important than the shear-induced clear-air turbulence they considered.
And there are other technical issues with the above article that could be a real problem. For example, weather observing systems have been greatly expanded and enhanced over the past 40 years, allowing observations to better identify atmospheric structures that can create turbulence. The massive addition of satellite data and aircraft observations took place during the period when the Reading team said the threat was growing the most. Is the threat really increasing or is our ability to identify strong wind shear layers getting better. They don’t say.
In summary, I believe there is no credible research showing a significant increase in aircraft turbulence due to changing climatic conditions. The media is making people worry about flying unnecessarily.
