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Floods and storms: we ainít seen nothing yet

By Julian Cribb - posted Thursday, 10 February 2011


Unprecedented floods and cyclones in Australia. Floods in Brazil and Pakistan. Huge snow dumps and storms in North America and Europe. Where is all the moisture coming from?

Out of the sky, obviously - but how’s it getting there?

The physics is straightforward. If you boil a pot of water, as you turn up the heat more water escapes as steam: evaporation increases as heat rises. Also, warmer air holds more moisture. There’s no mystery about it.

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When this warm wet air collides with mountain ranges or undergoes convection, it reaches a point where it lets go its water content in the form of a deluge. The heat released as the water vapour condenses back into water at high altitude drives the convection process even harder, and you get even bigger dumps of rain and more flooding. Driving it all is one of the three hottest years in human history.

Anyone who still thinks this is natural climate variability at work needs to think again. The processes now under way mean that storms, heavy rainfall and floods can only get more severe from here on. That one-off tax levy to pay for the damage is liable to become a regular impost.

This should not amaze us. Australian scientists were among the first to warn that a warming atmosphere would bring bigger rain dumps and more flooding. That was in 1992, ladies and gentlemen, almost two decades ago.

Writing in the journal Climate Dynamics, CSIRO researchers Hal Gordon, Penny Whetton and Barrie Pittock, Anthony Fowler and Malcolm Haylock reported an experiment in which they had doubled CO2 in the atmosphere in a climate model which pointed to much heavier rainfall in the tropics and subtropics and more drought in the mid-latitudes. “The findings have potentially serious practical implications in terms of an increased frequency and severity of floods in most regions,” they concluded.

The researchers were concerned that their results, obtained from one of the earlier and less elaborate climate models, might be taken out of context or exaggerated by others and debated for a time whether or not to release them. But they concluded the findings were sufficiently serious to warrant their being brought to public attention.

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In 1995 the warning was underscored in a paper by Anthony Fowler and Kevin Hennessy, who had run the scenario in three different climate models and obtained predictions of increased flooding rains that were consistent with the earlier ones and with current observations. They basically warned that flood prevention measures were likely to fail twice as often in a world with twice the atmospheric CO2, and this posed an unacceptable risk, especially for the poor and those living in flood-prone areas.

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About the Author

Julian Cribb is a science communicator and author of The Coming Famine: the global food crisis and what we can do to avoid it. He is a member of On Line Opinion's Editorial Advisory Board.

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