Warmer atmosphere may be to blame for changes in water cycle
More water moved into and out of the atmosphere in 2000 than in 1950, making saltier parts of the world’s oceans saltier and fresher waters less salty, researchers report in the April 27 Science.
A warming planet may to blame. Simulations in the new study suggest evaporation and rainfall got a 4 percent boost as surface temperatures rose half a degree Celsius. That boost is a bigger change than previous studies had suggested, but fits with the idea that a warmer atmosphere can hold more moisture.
“We see big broad patterns of change,” says Paul Durack, an oceanographer at the Lawrence Livermore National Laboratory in California. “Regions dominated by evaporation became saltier, while regions dominated by rainfall became fresher.”
Measuring such global changes in Earth’s evaporation and rain cycle has never been easy. Rain gauges on land or at sea tend to be sparsely distributed, and the exact positions of such instruments decades ago isn’t always known.
“Comparing different times gets difficult because you typically have more and better data for the later times,” says William Ingram, an atmospheric physicist at the Met Office Hadley Centre in Exeter and the University of Oxford in England.