Eco-Aviation Channel

Contrail theory challenged

By Geoffrey Thomas
Eco-Aviation Today, June 10, 2009, p.4

One of the least understood and most contentious issues surrounding aviation's impact on the environment has been the potential contribution of contrails to climate change. During the grounding of the US commercial airline fleet in the days following 9/11, scientists at the University of Wisconsin claimed that the absence of contrails was responsible for a 1.1 deg. C (2 deg. F) change in temperature over the US.

Now researchers in the UK and Germany, using computer modeling not available in 2001, claim that that the change in the daily temperature range was owing to a statistical quirk in the weather and the contrails only had a marginal effect.

"The theory is that contrails suppress DTR by cooling daytime temperatures and warming nighttime temperatures, so in their absence DTR increases," Prof. Piers Forster from UK's University of Leeds said in a report. While contrails over the US do suppress DTR, it is only by a fractional amount.

In fact, Leeds claims it would take 200 times more flights over the US than there are today to see the DTR change to the numbers postulated by the University of Wisconsin. With partner UK-based Omega, the UK school is conducting a two-year study into aviation contrails and greenhouse gas emissions using one of the world's foremost climate models, that of the Hadley Centre, part of the UK Met Office.

Separately, dissipation of contrails with a microwave beam behind aircraft engines is being flagged as a possible solution. Last year at a "Towards Sustainable Aviation Propulsion" conference organized by the Institution of Mechanical Engineers, Cranfield University's Frank Noppel said his research has led to Rolls-Royce filing a patent on what he believes could be a cost-effective contrail avoidance technology.

Noppel told delegates that ice particles could be prevented from forming, or be evaporated once formed, by remotely heating them together with condensation nuclei such as soot in the exhaust plume: "The remote heating of condensation nuclei could be achieved by applying electromagnetic radiation, such as microwaves. Depending on assumptions made, calculation shows that the power required for such a device could be as little as 0.1% of the engine power."

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