Contrails : Scars Across The Sky

January 21st, 2012
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I awoke this morning to another beautiful start to a day in the bush – eucalyptus scented air, the chatter of birds and a stunning sunrise. There were only the sounds and sights of nature – or so I initially thought.
When I looked up at the sky, it was marred by a couple of contrails. 
Contrail is short for condensation trail, a streak of artificial cirrus cloud made by jet aircraft engine exhaust; also known as a vapour trail. The scars left across the sky are another marker of our conquest of the planet; visible from our cities, suburbs, out in the boonies and increasingly, even the most remote regions of the world.
How contrails form
Contrails aren’t smoke – such as what might belch from a poorly maintained car – they are more akin to the clouds of fog you see emanating from car exhausts on a very cold morning. 
Formation is a similar process with contrails – as water vapor in exhaust gases rapidly cools, a cloud of very small water droplets forms, or they may turn into tiny ice crystals; particularly if the vapor binds with exhaust particles.
Contrails are usually formed at above 26,000 feet; where temperatures are at or below -40C (-40F) states Wikipedia.
Unlike the clouds of fog from a car’s exhaust that tend to dissipate rapidly, contrails can hang in the sky for minutes, even hours – and this is where an environmental threat lies. Aside from the other chemicals and particulates being spewed out in the exhaust, contrails are thought to have an impact on climate.
Contrails and the environment
According to a 2004 study entitled “Contrails, Cirrus Trends, and Climate” (PDF), contrails have the potential for affecting climate via radiative forcing.

Radiative forcing is the change in net irradiance between different layers of the atmosphere. The Intergovernmental Panel on Climate Change (IPCC) defines it as “a measure of the influence a factor has in altering the balance of incoming and outgoing energy in the Earth-atmosphere system.”

The study states like natural cirrus clouds, the artificial contrail clouds reflect solar radiation, while absorbing and emitting thermal infrared radiation. Additionally, ozone formed from air traffic exhaust can produce more positive radiative forcing, resulting in additional warming of the troposphere below .
Contrails have already been observed to affect regional weather in areas experiencing heavy air traffic. As air travel increases and expands, the impact may become “globally significant” states the study.

While the word “weather” is associated with short term events, “climate” is in relation to the longer term – and with contrails criss-crossing the skies and a permanent feature of some regions; the move from weather to climate isn’t such a big jump.
Avoiding contrail formation
Given contrail formation occurs at great heights, researchers from the Department of Civil & Environmental Engineering and the Department of Physics at Imperial College London suggested some years back that jet aircraft should fly below 31,000 feet in the summer and below 24,000 feet in the winter. 
However, there is a trade-off – fuel efficiency. By addressing the threat posed by contrails, it could exacerbate others such as an increase in other forms of pollution from aircraft exhaust. The researchers believe this is the lesser of the environmental evils though.
While the contrails I spot above my patch from time to time aren’t going to send temperatures in the area skyrocketing or plummeting, nor directly cause a flood/drought/tornado/whatever; it’s just another disturbance on an already very disturbed planet and not one to be disregarded.
It’s also a reminder that just because something isn’t happening in our own backyards, it doesn’t mean what is going on in someone else’s, even thousands of miles away, won’t impact all of us in the long run.

Michael Bloch
Green Living
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