Letter: Gas vapours

Sir: One can but welcome Nelson Cunnington's concern for scientific literacy in environmental matters (Letters, 11 July). In the same spirit of accuracy, one should record that water vapour, in common with virtually all tri- atomic gases, is, in fact, a powerful greenhouse gas.

Without the benefit of the "benign greenhouse" effect caused by water vapour, the earth would have a mean temperature well below freezing. The other greenhouse gases, carbon dioxide, methane etc, add to the warming caused by the water vapour with a resultant enhanced greenhouse effect.

Professor E H BILLETT

Brunel University

Isleworth, Middlesex