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The pace of climate change will be amplified because increased amounts of water vapour in warm air contribute to global warming by trapping heat radiated from the Earth, according to a new study.
Brian Soden from Princeton University, United States, and colleagues analysed the cooling and decrease in water vapour that followed the eruption of Mount Pinatubo in the Philippines in 1991.
By testing model predictions, they found that water vapour plays a warming role similar to that which is assumed in most climate models.
The findings, published in the 26 April issue of Science, help clear up one of great unknowns in climate modelling: how strongly water vapour contributes to warming.
Water vapour should almost double the sensitivity of climate to greenhouse gas increases. But some scientists say that insufficient understanding of the cloud processes that supply and deplete water vapour mean that it is not possible to gauge the importance of the effect.
The new study helps dispel these doubts and suggests that positive water vapour feedback will cause a substantial climate response.
Reference: Science, 26 April 2002