There are some good news and some bad news. The bad news is that this increases the global warming. The good news is that, surprisingly, this hasn't caused an increase in storms or floods.
"A key question in the global climate debate is if the climate warms in the future, will the water cycle intensify and what will be the nature of that intensification," said Thomas Huntington from the United States Geological Survey (USGS). "This is important because intensification of the water cycle could change water availability and increase the frequency of tropical storms, floods, and droughts, and increased water vapor in the atmosphere could amplify climate warming."
Huntington has reviewed more than 100 peer-reviewed studies about various aspects of the global water cycle in the last century. He found that, on a global scale, precipitation, evaporation, the levels of atmospheric water vapor, soil moisture, evapotranspiration, surface runoff, the lengthening of seasons, the quantities of snow on mountains in the winter are all increasing. (See water-cycle picture below for the meaning of the special terms.) Surprisingly, this is not correlated with an increase in the frequency or intensity of tropical storms or floods over the past century.
"This intensification [of the global water cycle] has been proposed and would logically seem to result in more flooding and more intense tropical storm seasons. But over the observational period, those effects are just not borne out by the data in a consistent way," said Huntington.
However, given that water vapor is the main greenhouse gas, this is a major contributing factor to global warming. This is a further indicative that the Kyoto Protocol, focusing on CO2 reduction, is not paying attention to the most important factor behind global warming - water vapors - which dwarfs the effects of other greenhouse gases such as carbon dioxide and methane. But, as the level of water vapors are largely outside of our control, it means that reversing global warming may be impossible to do, and that we should focus instead on dealing with the effects.
Thus, one should try to determine as accurate as possible what these effects would be.
"We are talking about two possible overall responses to global climate warming: first an intensification of the water cycle being manifested by more moisture in the air, more precipitation, more runoff, more evapotranspiration, which we do see in this study; and second, the potential effects of the intensification that would include more flooding and more tropical storms which we don't see in this study," said Huntington. Picture and image credit: Mark Owens; USGS