In a paper published today in the journal Science, Australian scientists from CSIRO and the Lawrence Livermore National Laboratory, California, reported changing patterns of salinity in the global ocean during the past 50 years, marking a clear fingerprint of climate change.
Lead author, Dr Paul Durack, said that by looking at observed ocean salinity changes and the relationship between salinity, rainfall and evaporation in climate models, they determined the water cycle has strengthened by four percent from 1950-2000. This is twice the response projected by current generation 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 Durack.
With a projected temperature rise of 3ºC by the end of the century, the researchers estimate a 24 per cent acceleration of the water cycle is possible.
Scientists have struggled to determine coherent estimates of water cycle changes from land-based data because surface observations of rainfall and evaporation are sparse. However, according to the team, the global oceans provide a much clearer picture.
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.
In the study, the scientists combined 50-year observed global surface salinity changes with changes from global climate models and found “robust evidence of an intensified global water cycle at a rate of about eight percent per degree of surface warming."
Dr Durack said the patterns are not uniform, with regional variations agreeing with the ‘rich get richer’ mechanism, where wet regions get wetter and dry regions drier. He said a change in freshwater availability in response to climate change poses a more significant risk to human societies and ecosystems than warming alone.
“Changes to the global water cycle and the corresponding redistribution of rainfall will affect food availability, stability, access and utilization,” Dr Durack said.
Dr Susan Wijffels, co-Chair of the global Argo project, leader of the Argo Facility in IMOS, and a co-author on the study, said maintenance of the present global fleet of around 3,500 Argo profilers is critical to observing continuing changes to salinity in the upper oceans.