May 21st, 2012 by James Ayre
The Earth’s water cycle is intensifying, leading to more evaporation in dry climates and more rain in wet climates.
“A clear change in salinity has been detected in the world’s oceans, signalling shifts and an acceleration in the global rainfall and evaporation cycle.”
A new study just published in the journal Science reports changing patterns of salinity in the global ocean during the past 50 years, serving as a clear fingerprint of the changing climate.
The study says that by looking at the changes in ocean salinity, and the relationship between salinity, rainfall, and evaporation in climate models, it shows that the water cycle has strengthened by four percent from 1950-2000.
That’s twice the response that’s been estimated by current global climate models.
“Salinity shifts in the ocean confirm climate and the global water cycle have changed.
“These changes suggest that arid regions have become drier and high rainfall regions have become wetter in response to observed global warming,” said Dr Paul Durack, lead author and a post-doctoral fellow at the Lawrence Livermore National Laboratory.
With the conservative temperature rise estimate of 3 degrees Celsius by 2100, the researchers estimate that a 24% intensification of the water cycle is possible.
In the past, scientists have had a hard time getting good estimates of land-based water cycle changes because observations are sparse. But the global oceans offer a much clearer picture according to the researchers.
“The ocean matters to climate — it stores 97 per cent of the world’s water; receives 80 per cent of the all surface rainfall and; it has absorbed 90 per cent of the Earth’s energy increase associated with past atmospheric warming,” said co-author, Dr Richard Matear of CSIRO’s Wealth from Oceans Flagship.
“Warming of the Earth’s surface and lower atmosphere is expected to strengthen the water cycle largely driven by the ability of warmer air to hold and redistribute more moisture.”
The intensification is from the patterns of evaporation and rainfall being enhanced. Global oceans cover 71 percent of the planet, so any changes in this pattern are clearly reflected in ocean surface salinity.
For the study, the researchers combined 50 years of observed changes in ocean surface salinity with changes from global climate models, finding “robust evidence of an intensified global water cycle at a rate of about eight per cent per degree of surface warming.”
The patterns aren’t uniform though — the drier areas are being further dried out, while the wettest regions are receiving even more rainfall.
Changes in freshwater availability are a clear threat, and pose a much more significant risk to human societies and ecosystems than warming itself.
“Changes to the global water cycle and the corresponding redistribution of rainfall will affect food availability, stability, access and utilization,” Dr Durack said.
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