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Airspace Article
Avoiding the establishment of climate warming contrails is clearly desirable. This could be achieved through modifications to fuel or engines.
Most obvious though, and crucial to the work of air navigation service providers, is deviating flights around airspace which is likely to form contrails, known as Ice Super Saturated Regions (ISSRs). As the Imperial College London study suggests, the majority of contrails are formed by a minority of flights.
Targeting specific flights that have a high chance of producing contrails, and varying their flight path could prevent much of the climate damage. This may involve a fuel burn penalty, but contrail-forming regions are vertically thin, meaning that a small adjustment in altitude may be sufficient. Figures from MIT suggest that this is just 0.5% when averaged out across the entire fleet. In other words, it may be vastly more beneficial – in climate warming terms – to re-route a flight than to create a contrail.
While a number of airlines and stakeholders are doing flight trials, more work is needed to enhance our ability to accurately forecast airspace likely to be conducive to the creation of persistent contrails and to understand the effects of mitigation at scale. What would be the impact on air traffic flows and congestion if all flights routinely avoided contrail-forming regions?
Although a huge amount of work is ahead, there is hope that mitigating the carbon and non-carbon climate impacts of aviation is within aviation’s grasp. ANSPs will have a big role to play.
Contrail avoidance
“Contrails can be cooling, usually during the day when you have this reflection of sunlight, or they can be warming, particularly at night, the science tells us that the average contrail is warming. But that does not mean every contrail is warming.”
Florian Allroggen
Executive Director, Laboratory for Aviation and the Environment, MIT,
The main questions arising from this focus on the extent of the impact of contrails and the mitigation strategies that would then make economic and environmental sense.
Regarding the impact, measuring contrails in a scientifically meaningful way is difficult. Backward-facing cameras will not reveal persistence while sensors have several technical challenges to overcome. Likewise, off-the shelf weather forecasting software is not designed to predict contrail-forming regions.
Nevertheless, studies and trials are ongoing. One study, from Imperial College London, suggested that diverting just 1.7% of flights could reduce the climate damage of contrails as much as 59%.
Quantifying impact
As contrails become diffused, they end up looking and behaving like a cirrus cloud. And, as with clouds, contrails can therefore change the energy balance of the atmosphere. The science for this is well established. When contrails reflect sunlight back into space, they have a cooling effect on the climate. But when they trap outgoing thermal radiation, effectively insulating the planet from heat loss, they have a warming effect.
Speaking at the International Air Transport Association (IATA) Annual General Meeting, Florian Allroggen, Executive Director, Laboratory for Aviation and the Environment, MIT, explained that the impact for each and every contrail is therefore situational. Not every contrail is created equal.
“Contrails can be cooling, usually during the day when you have this reflection of sunlight, or they can be warming, particularly at night,” he said. “The science tells us that the average contrail is warming. But that does not mean every contrail is warming.”
Contrail science
Aviation affects the environment in numerous ways. About 70% of emissions from an aircraft tailpipe is carbon dioxide (CO2), which is known to have a warming effect on the climate. Water vapour makes up the majority of the remainder with about 1% made up of nitrogen oxides (NOx), sulphur dioxides, and other chemicals.
All have an impact. NOx can also have a warming climatic effect, for example, but the scientific consensus suggests this is not significant. Rather, NOx is an immediate air pollution problem as it leads to particulate formation, which in turn causes health issues. Similarly, noise is an immediate challenge, as opposed to the far longer-term consequences of CO2.
Contrails, or condensation trails, the white lines formed from an aircraft’s engines, have also come under scrutiny. They do not form routinely, requiring both cold air and humidity to allow water to freeze around particles to form the contrail.
Non-persistent contrails – those that dissipate within a few minutes – are not thought to be environmentally significant as they simply do not remain in the atmosphere long enough. Contrails that keep their linear shape or persist in a diffused state, sometimes for hours, are more concerning, however.
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Avoiding the establishment of climate warming contrails is clearly desirable. This could be achieved through modifications to fuel or engines.
Most obvious though, and crucial to the work of air navigation service providers, is deviating flights around airspace which is likely to form contrails, known as Ice Super Saturated Regions (ISSRs). As the Imperial College London study suggests, the majority of contrails are formed by a minority of flights.
Targeting specific flights that have a high chance of producing contrails, and varying their flight path could prevent much of the climate damage. This may involve a fuel burn penalty, but contrail-forming regions are vertically thin, meaning that a small adjustment in altitude may be sufficient. Figures from MIT suggest that this is just 0.5% when averaged out across the entire fleet. In other words, it may be vastly more beneficial – in climate warming terms – to re-route a flight than to create a contrail.
While a number of airlines and stakeholders are doing flight trials, more work is needed to enhance our ability to accurately forecast airspace likely to be conducive to the creation of persistent contrails and to understand the effects of mitigation at scale. What would be the impact on air traffic flows and congestion if all flights routinely avoided contrail-forming regions?
Although a huge amount of work is ahead, there is hope that mitigating the carbon and non-carbon climate impacts of aviation is within aviation’s grasp. ANSPs will have a big role to play.
Contrail avoidance
The main questions arising from this focus on the extent of the impact of contrails and the mitigation strategies that would then make economic and environmental sense.
Regarding the impact, measuring contrails in a scientifically meaningful way is difficult. Backward-facing cameras will not reveal persistence while sensors have several technical challenges to overcome. Likewise, off-the shelf weather forecasting software is not designed to predict contrail-forming regions.
Nevertheless, studies and trials are ongoing. One study, from Imperial College London, suggested that diverting just 1.7% of flights could reduce the climate damage of contrails as much as 59%.
Quantifying impact
All have an impact. NOx can also have a warming climatic effect, for example, but the scientific consensus suggests this is not significant. Rather, NOx is an immediate air pollution problem as it leads to particulate formation, which in turn causes health issues. Similarly, noise is an immediate challenge, as opposed to the far longer-term consequences of CO2.
Contrails, or condensation trails, the white lines formed from an aircraft’s engines, have also come under scrutiny. They do not form routinely, requiring both cold air and humidity to allow water to freeze around particles to form the contrail.
Non-persistent contrails – those that dissipate within a few minutes – are not thought to be environmentally significant as they simply do not remain in the atmosphere long enough. Contrails that keep their linear shape or persist in a diffused state, sometimes for hours, are more concerning, however.
Aviation affects the environment in numerous ways. About 70% of emissions from an aircraft tailpipe is carbon dioxide (CO2), which is known to have a warming effect on the climate. Water vapour makes up the majority of the remainder with about 1% made up of nitrogen oxides (NOx), sulphur dioxides, and other chemicals.
As contrails become diffused, they end up looking and behaving like a cirrus cloud. And, as with clouds, contrails can therefore change the energy balance of the atmosphere. The science for this is well established. When contrails reflect sunlight back into space, they have a cooling effect on the climate. But when they trap outgoing thermal radiation, effectively insulating the planet from heat loss, they have a warming effect.
Speaking at the International Air Transport Association (IATA) Annual General Meeting, Florian Allroggen, Executive Director, Laboratory for Aviation and the Environment, MIT, explained that the impact for each and every contrail is therefore situational. Not every contrail is created equal.
“Contrails can be cooling, usually during the day when you have this reflection of sunlight, or they can be warming, particularly at night,” he said. “The science tells us that the average contrail is warming. But that does not mean every contrail is warming.”
Contrail science
Airspace Article