Nov 292015
 
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Mainz sports an unusually busy sky given its close proximity to Frankfurt International Airport. And quite often, maybe even every few minutes during the day, one just has to look up and see airplanes zipping across. In their wake, these vehicles leave behind long and wispy trails. Trails, not unlike those, of boats against the turquoise of the ocean. But if one patiently keeps on watching, he/she will be able to make out these trails combining to form cirrus clouds.

These trails are the ejected exhaust crystallizing under a supercooled condition and forming ice. In other words, they are very aptly named as condensation trails or contrails for short. Subsequently, these clouds then act as a blanket and trap the heat radiating from the surface…an impromptu greenhouse effect…and just like a greenhouse they prevent the sun’s rays from reaching the surface also.

Contrails
Contrails : Benign or Not ?

A 1999 report by the IPCC revealed an inconvenient truth – a 15 percent increase in global warming within the next 5 decades from aircraft carbon emissions [1]. Several international think-tanks including NASA over the last fifteen years have tried to promote zero-emission flights but results have not been commercially viable for long-haul flights yet. Still it remains one of the big challenges going forward [2]. So one must really take stock and think about where are we flying to.

Fortunately, not all is lost just yet. Researchers, after meticulously combing through 20 years of flight data over the busy North Atlantic flight route, have shown from calculations that even a small detour for long haul flights of around 100 km can lead to something quite unexpected [3]. Their predictions indicate it would not only reduce the formation of a serpentine mile long contrails which would trap more heat but also at no added cost to the environment compared to CO2 emissions from the jets themselves.

So yes, we may have 10 year old statistics stating the obvious misuse of our carbon footprint [4] but hey, those ethereal formations may yet have a silver lining.

– Soham Roy

References:
[1] http://www.ipcc.ch/publications_and_data/publications_and_data_reports.shtml
[2] https://longitudeprize.org/challenge/flight
[3] E.A. Irvine et al., “A simple framework for assessing the tradeoff between the climate impact of aviation carbon dioxide emissions and contrails for a single flight”, Environ. Res. Lett., 2014, 9, 064021.
[4] D.S. Lee et al., “International Emissions”, UNEP ‘Bridging the emissions gap’, 2011, 4, 40.

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