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In his article on dangerous ideas ("A kind of intellectual cancer", 21 May) Alec Ryrie proposes a thought experiment in which he asks "if we found a cheap and effective way to scrub greenhouse gases from the atmosphere, would that make it OK to go on emitting them? And if not, why not?"

I have an idea that might advance this debate. Why don't we build a very tall chimney - or series of chimneys - tall enough to clear the Earth's atmosphere and pump greenhouse gases from the planet into space? Instead of polluting our own planet, we might in this way pollute the rest of the Universe!

Can't be done, you say? Such an idea has already been proposed by the late Arthur C. Clarke in The Fountains of Paradise, to create a reusable and hence cheaper way of getting to outer space - a kind of tall lift or stairway to heaven, in fact, with its base on the equator and the other end tethered to a satellite in geostationary orbit.

Ken Smith, Senior lecturer in criminology, Bucks New University.