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Earth getting steamier and steamier


Warmer air holds more water vapour, a greenhouse that stokes the warming effect and so worsens humidity (Image: iStockphoto)


The findings, published today in the journal Nature, are some of the first to suggest how human-produced greenhouse gases have affected global humidity levels in recent decades.

The results could also offer clues on future climate change, the researchers say.

"It is another piece of the puzzle that climate change is happening and we are influencing it," says Dr Nathan Gillet, a climate researcher at the University of East Anglia.


Scientists say average global temperatures will rise by 2-6°C by the end of the century, causing droughts, floods and violent storms.

Warmer air can hold more water vapour.

"It has been predicted for a long time that humidity would increase with greenhouse gas increases," says Gillet, who led the study.

"But this is the first study that shows a significant human impact on surface humidity," he says.

Previously, scientists 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.

Weather stations, buoys and ships



"It is getting moister at the surface, so humidity is increasing," he says. "You only see that in the model with the human effect."

From 1976 to 2004, when the world's average surface temperature rose 0.49°C, global levels of atmospheric water vapour rose 2.2%, according to the paper.

By 2100, humidity levels could increase by another 10%, says Gillett.

Worse in the tropics



Gillett says water vapour is a positive feedback, or a vicious circle, in the global warming equation.


Tags: climate-change, weather