Trails: how changing flight plans can help the climate

Those thin white lines that cross the skies after an airplane flies overhead are far less benign than their fluffy patterns might suggest.

Until now, governments and industry have firmly focused on reducing CO2 emissions from aircraft – with good reason, such as the aviation sector is responsible for around 2.4% of global CO2 emissions and a single flight can emit the same amount of CO2 as many people in an entire year.

But some scientists now warn that the impact of radiation from aircraft trails could be even more significant. Contrails, which increase the effect of global warming through warming, it can account for more than half (57%) of the entire aviation climate impact.

Contrails (contrails for short) are water vapor that condenses in the form of ice on the soot particles emitted by aircraft engines. They do not always occur as they require certain atmospheric conditions: the air must be very cold, humid and “supersaturated” for ice to form.

They trap and absorb the outgoing heat that otherwise dissipates into space. This gets worse at night when it gets colder and the wake lasts longer. They can also have a less significant cooling effect, blocking incoming sunlight, but only during the day.

They can last for a second, hours or even a day – and this determines the climatic impact that a particular contrail will have. But recent research shows there may be a solution to this overlooked problem.

Professor Marc Stettler, Professor of Transport and Environment at Imperial College London, says that changing the altitude of less than 2% of flights could potentially reduce contrail-related climate change by a staggering 59%. “Changing the flight elevation by just a thousand feet can prevent contrails,” he explains.

The adjustments would mean that a plane could avoid some of the regions of the atmosphere that are cold and humid enough to create contrails in the first place.

“A relatively small percentage of flights contribute most of the climate impact. So if we can modify these flights, we can significantly reduce the climate impact,” says Prof Stettler.

Recent search by Prof. Christiane Voigt, head of the cloud physics department at the University of Mainz, Germany, points out.

It has conducted trials with the German Aerospace Center (DLR) to measure and mitigate the impact of contrails.

His team uses high-altitude, long-range G55 research aircraft (HALOs) to collect their data. The aircraft carries wing-mounted instruments that measure the properties of contrails and scattered light from radiation. This allows them to assess the accuracy of predictions and investigate the impact of radiation.

“Our results have been really positive. We were able to predict and avoid around 80% of the trails at a low cost,” he says. Professor Voigt adds that very few flights would have to be diverted to achieve a “big climate impact”.

Although there were some uncertainties, his team was able to track most of the trails and avoid the correct areas.

“We are at the beginning of a race to avoid them. And I have the impression that [companies] like Lufthansa and Airbus, they are really interested, as it is economical and effective, “he says.

Royal Aeronautical Society colleague Professor Keith Hayward is optimistic that only a software change may be required to adjust many flight plans to avoid contrails and that this could be done at a relatively low cost.

Compared to the typical $ 200 million cost of a passenger plane or engine modifications that can go as high as $ 12 million, a software modification is relatively inexpensive, he says.

The professor. Hayward says the next challenge for airlines is figuring out how it is possible to make altitude changes of “a few thousand feet” during the flight to avoid contrails and at the same time not disturb passenger comfort. A pilot should spot them in “enough time for a plane to fit gracefully,” he adds.

But Professor Voigt doesn’t think this is necessarily a problem. He thinks flight comfort could improve as flight paths will avoid some of the water vapor areas in the sky, which both form contrails and cause irregular turbulence.

Raimund Zopp, former pilot and co-founder of the Austrian flight services software company, Flightkeys, is working on the contrail displays to be programmed into flight plan technology. The airline plans to include contrail avoidance in its customers’ flight plan trajectories by 2023.

“Only a small fraction of the flights are causing the problem, so changing a few flight plans is enough to have a huge effect,” he says.

As a former pilot, Zopp says that from a flight procedure perspective, adding this information would be easy. “Flight plans are programmed into the air system navigation, but pilots need training on this new aspect of the flight plan profile contrail.”

Any action on climate change that is not directly related to reducing emissions is further down the list of priorities for governments and industry, because CO2 is the most important greenhouse gas for most sectors.

However, unlike other sectors, aviation also has very significant non-CO2 impacts.

The professor. Settler believes that people have hesitated to reduce contrails by diverting flights due to fears that it would be completely unfeasible – that all flights may need to be modified or fuel consumption would dramatically increase. This latest research shows that this is not the case.

Dr. Jarlath Molloy, senior manager for environmental affairs at Aeronautical Information Service NATS agrees that until now there has been a lack of focus on non-CO2 related issues from the entire industry.

However, from an operational point of view, dealing with contrails is “just one more element that the plane should calculate,” he says, and could also be handled in a similar way to how authorities already organize groups of flights to avoid major storms. winter.

“We are exploring the feasibility and what we should do to manage flights looking for the same routes,” adds Dr. Molloy.

The Department of Transportation says it is “currently evaluating” a number of responses to its own Jet Zero consulting on how to “make the sector cleaner and greener” and that this strategy will “aim to address” the non-CO2 impact of aviation.

Meanwhile, atmospheric scientist Professor Ken Caldiera of the Carnegie Institution for Science makes a compelling case. He estimates that preventing most of the harmful climate impact from contrails would cost less than $ 1 billion (£ 720 million) annually and the net value of the benefit could be more than a thousand times higher.

“We don’t know of any comparable climate investment with a similarly high probability of success,” he said wrote in the scientific journal Nature.

So could a fine could focus minds in the aviation industry faster? Dr. Andrew Gettleman of the US National Center for Atmospheric Research says that although more research is needed, a contrail tax or avoidance discount could be introduced if a carbon tax is approved.

“We have not yet seen the overall regulatory framework for carbon in aviation, but once we have a broader regime to mitigate climate change and reduce carbon, we can adequately address the problem of contrails.”