The OPAL climate survey is a way you can help scientists investigate how our activities affect the climate – and how the climate may affect us. Dr Geoff Jenkins, Cloud Appreciation Society Member 23638 who is based at the University of Reading, has got in touch to see if C.A.S. members based in England would be interested help with one aspect of the survey: observing the appearance of condensation trails.

You will all have seen condensation trails, or contrails, in the sky. They are the white lines left behind high-flying aircraft (described on page 63 of The Cloud Collector’s Handbook). The man-made clouds are formed when the air is cold (below about minus 40°C) – usually above about 10km (30 000ft). At this low temperature, water vapour ejected from jet engines (created when fuel is burnt) quickly condenses into ice crystals. If the air is moist enough, the contrail can stick around for a long time, and even spread out to form cirrus-like clouds – and these may be warming the climate (although much less than greenhouse gases do). The purpose of the survey is to try and find out more about how contrails affect our temperatures.

Since Cloud Appreciation Society members are such keen observers of the sky, they would be perfect participants in the survey. And it couldn’t be simpler to contribute. All you have to do is tell the boffins when you see contrails in the sky. They are interested in observations at any time of day and on as many days as possible between March and May this year. You don’t even have to register (unless you want to get a field pack and to keep track of your results). As they come in, the results are added to a contrail observations map.

Understanding the effect of these man-made clouds on our temperatures is of increasing imporance. The ubiquity of air travel means that more and more contrails spread across our skies with every passing decade. So, between now and the end of May (2011), if you are based in England, please contribute to the contrail study by reporting your observations on the OPAL website here:
http://www.opalexplorenature.org/contrails