Revisiting the lower stratospheric water vapour trend from the 1950s to 1970s

Previous work showed a near-continuous increase in stratospheric water vapour between the 1950s and 1990s from a variety of instruments, without recourse to fits between instruments. We reassess the trend from the earliest, the UK frost-point hygrometer, 1954–1976. An error in previous work omitted to transform values from ppmm to ppmv. When corrected, they fit more convincingly with measurements by later frost-point hygrometers. Minor instrument changes between the 1950s and 1970s do not introduce a potential bias to the trend but do increase its error. If the full 1970s data are included, the trend becomes 2.1 ± 0.8%/year (two-sigma).