A study published in the journal Science has concluded that climate change is altering oceans and rainfall worldwide. A team of three researchers looked at ocean data over the period 1950 to 2000. The research found salinity levels have changed in all the world’s oceans, wetter areas are experiencing more rain and drier areas have become drier.
Susan Wijffels from the Commonwealth Scientific and Industrial Research Organisation – CSIRO – says she expects the trend to continue.
“The answer of how much more is going to be in the future depends on how much more warning there is going to be,” she said. “So if we stay on a high emissions pathway we might see warming up around three degrees, which will give us maybe a 24 per cent change in our water cycle.”
The authors say this could have implications for global food security. In the paper, Australian scientists from the 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 per cent 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, a post-doctoral fellow at the Lawrence Livermore National Laboratory.
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, 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,” 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.”
He said the intensification is an enhancement in the patterns of exchange between evaporation and rainfall and with oceans accounting for 71 percent of the global surface area the change is clearly represented in ocean surface salinity patterns. 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 per cent per degree of surface warming,” Dr Durack said.
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.
Ocean salinity FAQs [pdf]
Argo is an observation system for the Earth’s oceans that provides real-time data for use in climate, weather, oceanographic and fisheries research. Argo consists of a large collection of small, drifting oceanic robotic probes deployed worldwide. The probes float as deep as 2 km. Once every 10 days, the probes surface, measuring conductivity and temperature profiles to the surface. From these, salinity and density can be calculated. The data are transmitted to scientists on shore via satellite. The data collected are freely available to everyone, without restrictions. The initial project goal was to deploy 3,000 probes, completed in November 2007.
The Argo program is a collaboration between 50 research and operational agencies from 31 countries. Argo is a component of the Integrated Ocean Observing System.
The Argo program was designed to operate on the same 10-day duty cycle to match the existing satellite measurements of the ocean’s sea surface. These satellites, calledTopex/Poseidon and Jason 1, measure changes in the surface topography of the ocean. With such measurements, information about temperature, mass redistribution, or surface currents can be inferred. The Argo floats measure subsurface changes in temperature and salinity, hence the float measurements are complementary to the altimetry.
Argo is named after the Greek mythical ship Argo which Jason and the Argonauts use on their quest for the Golden Fleece. The name was chosen to emphasize the complementary relationship of the project with the Jason-1 satellite altimeter.
Although drifting floats had been deployed during the World Ocean Circulation Experiment in the 1990s, Argo floats began to be deployed in earnest in the early 2000s. The target number of 3,000 deployed floats was reached during 2006–2007. The number of floats is continually changing as floats are lost or expire, while others are deployed. Nominally, some 750 floats are deployed each year to sustain the system. The floats have a nominal 300-km spacing, although the exact separations depend on the randomness of the float drift.
The Argo temperature and salinity measurements are yielding valuable information about the large-scale water properties and currents of the ocean, including the variability of these properties over time scales from seasonal to decadal :: Read More at Wikipedia »»»»