The Water Cycle, Moist Processes and Climate Change: What might be predictable, where challenges lie, and what we glean from new Earth observations

March 25, 2010

Graeme Stephens

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The planet’s water cycle is thought to be ‘accelerating’ under the scenario of global warming with projected increases in the occurrence of heavier precipitation among other expected responses. The physical basis for these claims is not firmly advanced and this lack of firm basis, casts a large shadow on validity of projected changes in precipitation that appear in recent climate assessment studies. In this seminar, the factors that control the change in character of global-mean precipitation will be discussed and a broad, physically based explanation for the change in the character of global precipitation is offered. The important way the water cycle connects to, and is controlled by the so-called water vapor feedback and the planet’s energy balance, will also be underscored. Those aspects of these controlling influences that are likely to change in a predictable way with climate warming will be underscored, further suggesting that some aspects of the response of the planet’s water cycle to climate change might similarly be predictable. Advances that have occurred in our understanding of these particular aspects of the climate system over the past decade will be also be emphasized, as will current limitations of global Earth-system models.