Climate change has accelerated the global water cycle, a new study suggests. The findings support one of two conflicting projections researchers have made about how the atmosphere’s cycle of precipitation and evaporation will evolve in response to global warming. Theoretical predictions, based on the relationship between temperature and the amount of water vapor the atmosphere can hold, suggest that global warming should intensify the atmospheric water cycle by about twice as much as the amount suggested by computer models. (These models incorporate additional factors, such as energy constraints in the atmosphere.)
Reliable measurements of the intensity of the water cycles are difficult to make, however, in large part because the oceans cover about 70 percent of the Earth’s surface and receive around 80 percent of its rainfall. Paul Durack and colleagues got around this problem by looking at sea-surface salinity measurements, collected from 1950 to 2000. The patterns of change in the salinity data are consistent with the theoretical projections rather than the computer simulations. The researchers conclude that the global water cycle will intensify by 16 to 24 percent if global average temperatures increase by to 2 to 3 C. One of the effects will be that ocean regions that are relatively fresh will become fresher, while salty regions became saltier, a change that is already underway, according to Durack and colleagues.
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