Contrails and Why They Matter:
13th April 2006
Donald Burfitt-Dons, GWA

The amount of sunlight reaching the earth’s surface has been steadily reducing since the sixties at 1.4% per decade. It is a widely accepted assumption that the greenhouse gases such as CO2 and methane, which we are releasing into the atmosphere, are causing this.

An additional factor of growing importance is the formation of contrails from the efflux of jet aircraft engines. When conditions are right the entire North Atlantic is covered by man-made cirro stratus at high level (typically around 10,000 metres or 33000 ft.) The North Atlantic Track System separates aircraft laterally by a nominal one degree (60 nautical miles), 1000 ft vertically and 15 minutes on the same track. As the upper winds, which can blow at anything up to 200mph in the jet stream, have the effect of dispersing the contrails, they join up with those on the adjacent track forming one continuous cloud layer. This adds to sun dimming i.e. the amount of sun reaching the earth is reduced. It has been calculated that at any given time contrails effect less than 2% of the earths surface. But with aircraft numbers forecast to rise steadily now is the time to speed up the development of technologies such as fuel cells which do not create water vapour.