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Matt Ridley is the author of provocative books on evolution, genetics and society. His books have sold over a million copies, been translated into thirty languages, and have won several awards.

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No contrails

Iceland's volcanic cloud keeps the sky clear of planes: will that cause more nocturnal cooling?

The sky's bright blue right now, which is weird because I am looking up through a 5,000-metre thick plume of volcanic ash from Iceland. This has stopped all flights in the UK air space and much of northern Europe.

(As somebody quipped on the radio, `Dear Iceland, we said send CASH'.)

So there are no vapour condensation trails from jets, which prompts the thought: did anybody ever figure out what con trails do to the climate?

One study estimated that the 3-day shutdown in US aviation after 9/11 increased diurnal temperature range by 1C!

Another study in the Journal of Climate in 2004 concluded that:

It is concluded that the U.S. cirrus trends are most likely due to air traffic

and

the cirrus trends over the United States are estimated to cause a tropospheric warming of 0.2-0.3C [per] decade

That's huge. Anybody know if these studies still hold up?