PARIS (AFP) — Man-made global warming is driving up humidity levels, with the risk that rainfall patterns will shift or strengthen, tropical storms intensify and human health may suffer from heat stress, a study released on Wednesday said.
From 1976 to 2004, when the world's average surface temperature rose 0.49 degrees Celsius (0.9 degrees Fahrenheit), global levels of atmospheric water vapour rose 2.2 percent, according to the paper by British scientists.
By 2100, humidity levels could increase by another 10 percent, lead researcher Nathan Gillett of the Climate Research Unit at the University of East Anglia, eastern England, told AFP.
Previously, scientists had noted an increase in humidity over the past few decades as higher temperatures sucked more water from the land and ocean surface.
But it was unclear whether these changes were the result of a natural or a human impact on the climate, as the data was regional rather than global and different methods were used to make the calculations.
The new paper is based on a new set of observations of humidity levels. This data was then crunched through a powerful computer model of Earth's climate system in the late 20th century.
Gillett said water vapour was a "positive feedback" -- a vicious circle, in scientific parlance -- in the global warming equation.
Steam is a greenhouse gas, meaning that like carbon pollution that results from burning fossil fuels, it traps solar heat in the atmosphere, thus stoking the warming effect and so worsening humidity.
The ramifications could be wide-ranging, he said. The distribution and intensity of rainfall could be affected, and tropical cyclones could be beefed up, as humidity is one of the fuels for these storms.
The study is published on Thursday in Nature, the weekly British science journal.
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