The atmosphere is becoming more humid in a pattern consistent with man-made climate change, researchers have found.
Humidity increases could affect weather around the world
Their study, reported in the journal Nature, confirms the global increase in humidity found in previous studies.
They say that the pattern of humidity increases in various parts of the world resembles that projected by computer models of man-made global warming.
Water vapour is a greenhouse gas, and it is thought that having more of it in the air could amplify temperature rise.
The major report released earlier this year by the Intergovernmental Panel on Climate Change (IPCC) said that this amplification was the largest "positive feedback" mechanism they had identified.
Previous research has shown that humidity increases in Europe, a response to higher temperatures, were amplifying the temperature rise by about a factor of two.
In the new study, researchers from the University of East Anglia and the UK Met Office's Hadley Centre analysed a dataset of humidity measurements made across the world.
Data came from weather stations, ships and buoys, painting a global picture.
The scientists compared the global and regional trends with the projections of a computer model developed by the Hadley Centre, which estimates the relative influences of natural cycles and increased concentrations of greenhouse gases such as carbon dioxide.
Human-induced changes, they calculate, have been the bigger factor behind the global humidity increase seen since 1975.
"This confirmation that humidity and temperature are increasing as expected has important implications for future human health and comfort," observed the Hadley Centre's Peter Thorne, one of the research team.
It could also have important implications for extreme weather events such as tropical cyclones and rainstorms.
Some of the scientific team were involved in another study, reported in July, which showed that human-induced climate change was behind trends of increasing and decreasing rainfall noted in various parts of the world.