The Science
What causes contrail formation?

Contrails form in jet engine exhaust where heat, water vapor and black carbon (soot) mix with the ambient atmosphere.


Soot particles and other aerosols form cloud nuclei that condense exhaust water vapor into liquid droplets. The exhaust plume sinks down and away from the aircraft due to the wake vortex.


The plume is diluted by ambient air, which cools the plume and freezes liquid droplets into ice particles. Persistent contrails can last hours and grow to become indistinguishable from natural cirrus clouds.

Contrails form in jet engine exhaust where heat, water vapor and black carbon (soot) mix with the ambient atmosphere.

Soot particles and other aerosols form cloud nuclei that condense exhaust water vapor into liquid droplets. The exhaust plume sinks down and away from the aircraft due to the wake vortex.

The plume is diluted by ambient air,

which cools the plume and freezes liquid droplets into ice particles. Persistent contrails can last hours and grow to become indistinguishable from natural cirrus clouds.

The Impact
How contrails affect global warming

Ice clouds, including natural and contrail-induced cirrus clouds, are better at trapping outgoing longwave (thermal) radiation emitted by the Earth than reflecting incoming shortwave (solar) radiation from the sun. This means that, in general, cirrus clouds trap more heat in the Earth's atmosphere than they reflect. These clouds continue to absorb outgoing radiation at night, even when there is no solar radiation to reflect.


The contrail impact on incoming and outgoing radiation is defined as the radiative forcing. Contrail radiative forcing depends on time of day, season, cloud cover, and albedo (reflectivity) of the surface of the earth.


In aggregate, contrails are strongly warming, increasing the overall heat stored in the Earth's atmosphere.

Ice clouds, including natural and contrail-induced cirrus clouds, are better at trapping outgoing longwave (thermal) radiation emitted by the Earth than reflecting incoming shortwave (solar) radiation from the sun. This means that, in general, cirrus clouds trap more heat in the Earth's atmosphere than they reflect. These clouds continue to absorb outgoing radiation at night, even when there is no solar radiation to reflect.


The contrail impact on incoming and outgoing radiation is defined as the radiative forcing. Contrail radiative forcing depends on time of day, season, cloud cover, and albedo (reflectivity) of the surface of the earth.


In aggregate, contrails are strongly warming, increasing the overall heat stored in the Earth's atmosphere.

Our Focus
How we can mitigate contrail impact
Intelligent route planning

Persistent contrails form in thin regions of the atmosphere (500 - 1000m thick in altitude) that are sufficiently cold and humid. Forecasts can predict where airplanes are likely to form warming contrails and enable pilots to avoid these regions.


Unlike fleet-wide adoption of DAC and SAF, this approach has a low cost and logistical footprint.

Sustainable aviation fuel

Sustainable aviation fuel (SAF) is biofuel produced from sustainable feedstocks used in place of traditional jet fuel. SAF has lower concentrations of aromatic compounds resulting in reduced soot emissions.


Studies of commercial flights using a blend of up to 50% SAF show a reduction of 50% to 70% in soot emissions. Contrails produced by planes burning a SAF blend show similar reductions in size and concentration of ice particles, decreasing their warming effect.


In 2019, only 0.1% of all aviation fuel was SAF, a number that is only forecast to increase to 2% by 2030.

New engine technology

Persistent contrails form in thin regions of the atmosphere (500 - 1000m thick in altitude) that are sufficiently cold and humid. Forecasts can predict where airplanes are likely to form warming contrails and enable pilots to avoid these regions.


Unlike fleet-wide adoption of DAC and SAF, this approach has a low cost and logistical footprint.

Intelligent Route Planning

Persistent contrails form in thin regions of the atmosphere (500 - 1000m thick in altitude) that are sufficiently cold and humid. Forecasts can predict where airplanes are likely to form warming contrails and enable pilots to avoid these regions.


Unlike fleet-wide adoption of DAC and SAF, this approach has a low cost and logistical footprint.

Sustainable aviation fuel

Sustainable aviation fuel (SAF) is biofuel produced from sustainable feedstocks used in place of traditional jet fuel. SAF has lower concentrations of aromatic compounds resulting in reduced soot emissions.


Studies of commercial flights using a blend of up to 50% SAF show a reduction of 50% to 70% in soot emissions. Contrails produced by planes burning a SAF blend show similar reductions in size and concentration of ice particles, decreasing their warming effect.


In 2019, only 0.1% of all aviation fuel was SAF, a number that is only forecast to increase to 2% by 2030.

New engine technology

Persistent contrails form in thin regions of the atmosphere (500 - 1000m thick in altitude) that are sufficiently cold and humid. Forecasts can predict where airplanes are likely to form warming contrails and enable pilots to avoid these regions.


Unlike fleet-wide adoption of DAC and SAF, this approach has a low cost and logistical footprint.

Our Focus
Why focus on route planning first?

With just minimal adjustments to only 5% of flight paths, we can eliminate 80% of contrails-induced warming.

Five Percent of Planes Re-Routed Eliminates 80% of Contrails-Induced WarmingDiagram showing 5% of planesDiagram of re-routing flight paths for contrail avoidance

The best available data indicates a kind of “super-Pareto principle” at play, where tweaking only a few flight paths would eliminate almost all of contrails-induced warming. In practice, this means that just 1 in 20 flights would need to fly over, under, or around areas of the sky predicted to produce harmful contrails.


Better yet, properly implemented, these adjustments would be cheap: Our studies show a fleet-average cost of roughly $5.00 per flight, or less than $0.50 per tonne of CO2 equivalent warming avoided.

Our Focus
Why focus on route planning first?

With just minimal adjustments to only 5% of flight paths, we can eliminate 80% of contrails-induced warming.

Five Percent of Planes Re-Routed Eliminates 80% of Contrails-Induced Warming

The best available data indicates a kind of “super-Pareto principle” at play, where tweaking only a few flight paths would eliminate almost all of contrails-induced warming. In practice, this means that just 1 in 20 flights would need to fly over, under, or around areas of the sky predicted to produce harmful contrails.


Better yet, properly implemented, these adjustments would be cheap: Our studies show a fleet-average cost of roughly $5.00 per flight, or less than $0.50 per tonne of CO2 equivalent warming avoided.

Our Focus
How the model works
How the model works diagram: weather forecast, modeling, flight planning and avoidance, verification
1
Forecast input

Weather forecasts, satellite images, flight locations, and other data are fed into contrail forecast models

2
Modeling

Models determine where harmful contrails are likely to occur and compare these predictions with observations

3
Flight Planning

Flight planners calculate the fastest route with the lowest fuel consumption accounting for contrail impact in their flight plan

4
Verification

Ground, air, and satellite observations verify contrail avoidance and feed back into forecasting models to improve data accuracy

Our Focus
How the model works
How the model works diagram: weather forecast, modeling, flight planning and avoidance, verification
1
Forecast input

Weather forecasts, satellite images, flight locations, and other data are fed into contrail forecast models

2
Modeling

Models determine where harmful contrails are likely to occur and compare these predictions with observations

3
Flight Planning

Flight planners calculate the fastest route with the lowest fuel consumption accounting for contrail impact in their flight plan

4
Verification

Ground, air, and satellite observations verify contrail avoidance and feed back into forecasting models to improve data accuracy

Our data
Observational data makes the model smarter
A image of a variety of contrails, where specific flight information has been overlaid on top of each contrail.
Ground-based observations inform real-time contrail avoidance and improve contrail forecast accuracy when they are fed back into the model.
Credit: Ed Gryspeerdt
A satellite image of the Earth's cloud cover, with contrails highlighted in red.
Southern United States seen from space. The red lines are contrails detected from the satellite imagery.
Credit: Google Research
Our data
Observational data makes the model smarter
A image of a variety of contrails, where specific flight information has been overlaid on top of each contrail.
Ground-based observations inform real-time contrail avoidance and improve contrail forecast accuracy when they are fed back into the model.
Credit: Ed Gryspeerdt
A satellite image of the Earth's cloud cover, with contrails highlighted in red.
Southern United States seen from space. The red lines are contrails detected from the satellite imagery.
Credit: Google Research
Our model
See what we're building
A data visualization showing a flight trajectory through space, with dots in a range of shades of red representing the evolution of contrails
We are building open tools and methods to advance a roadmap for contrail avoidance across the aviation industry. Build this data into your system using the Contrails API. Learn more on Github and py.contrails.org.
You can see these tools in action on the Contrail Map and the Contrail Navigator.
If you're interested in learning more about the science of contrails and contrail mitigation, read our contrails science primer.
Contact us for more information or to get involved.
Our model
See what we're building
A data visualization showing a flight trajectory through space, with dots in a range of shades of red representing the evolution of contrails
We are building open tools and methods to advance a roadmap for contrail avoidance across the aviation industry. Build this data into your system using the Contrails API. Learn more on Github and py.contrails.org.
You can see these tools in action on the Contrail Map and the Contrail Navigator.
If you're interested in learning more about the science of contrails and contrail mitigation, read our contrails science primer.
Contact us for more information or to get involved.
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