Contrail Fest over Eastern Washington

The satellite imagery over eastern Washington this morning looked like someone had gone crazy with a white crayon,  drawing many white lines, most extending roughly east-west.

Here is a closer view.   The white lines are contrails created by aircraft.

Look very closely, and you will see some black lines as well:  the shadows are produced by the contrails stopping the sun's light from reaching the surface.

Contrails are formed by the combustion of jet fuel in aircraft engines.  This combustion produces water vapor that condenses into water droplets, which eventually freeze into crystals in the cold temperatures aloft.   Combustion particles aid the condensation.

Contrails are thicker when the air is already close to saturation.  Thus, contrails are particularly obvious when the air aloft is already moist.   

Look closely at the satellite imagery above, and you will see a thin veil of cirrostratus clouds, indicating air already at saturation.  Adding more water from the jet engines simply makes the clouds thicker.

Or we can look at the temperatures (red lines) and dew points (green lines) from the radiosonde (balloon-born weather observations) at Forks, on the Washington Coast (below).  Near the level at aircraft fly (marked trop on the figure), temperature and dew point are nearly the same, indicating a moist atmosphere near saturation! (the Y-axis is height in terms of pressure; 500 is about 18,000 ft, 250 is about 35,000 ft).

Temperature (°C)

Climate Change and Contrails

Contrails both cool that atmosphere (by reflecting solar radiation to space) and warm it (by emitting infrared radiation down to the ground).   

A number of careful studies have found that the warming is dominant.  

Thus, contrails contribute to global warming.  Much, much less than CO2, but still a contribution.

One way to reduce this warming by contrails is to alter flight paths to avoid cirrostratus clouds or regions where the upper troposphere (where planes fly) is near saturation with water vapor.   Some folks have suggested this be done.

In any case, the effects of contrails are relatively small, much, much smaller than the aggregate effects of global CO2 increases.