Saltier oceans set scene for changes

Australia’s tropics will become wetter, and its central deserts drier, as the world’s oceans turn saltier faster than expected in response to climate change, new research says.

Using data from 4000 robotic probes, a team of scientists in Australia and the United States has measured a 50-year trend in increasing ocean salinity pointing to major changes in the world’s water cycle.

These include changes to current rainfall patterns and moisture evaporation rates that are occurring twice as fast as predicted and which will intensify extreme weather such as floods and droughts.

The findings, published today in the global journal Science, point to ”a clear fingerprint of climate change”, one of the paper’s co-authors, CSIRO oceanographer Richard Matear said.

”We’re looking at a much longer-term weather trend than La Nina,” Dr Matear said.

”We’d expect to see intensification of existing weather patterns and systems in a trend we’ve described as the rich getting richer. ”Regions like Queensland’s tropics will get significantly wetter, and areas like the central desert could become up to 10 per cent drier.”

Recent record rains across eastern Australia have been attributed to La Nina.

”What we’re seeing are bigger changes, that have long-term implications,” Dr Matear said.

As the Earth’s atmosphere warms, its capacity to hold and transport moisture increases. Ocean salinity is determined by rainfall and evaporation at the ocean surface, and the study has found these patterns are changing with high rainfall ocean areas becoming less saline and drier ocean regions becoming saltier.

The study estimated the increase in atmospheric moisture occurring for every degree of warming was slightly more than 7 per cent.

”So, with a projected temperature rise of three degrees by the end of the century, we estimate a 24 per cent acceleration of the water cycle is possible,” he said.

The paper’s lead author, Paul Durack, said by analysing salinity changes and the relationship between salinity, rainfall and evaporation, the research team was able to determine the world’s water cycle had strengthened by 4 per cent over 50 years. This was twice as fast as predicted by current climate models.

Dr Durack, a post-doctoral fellow at the Lawrence Livermore National Laboratory in California, said scientists had struggled to determine estimates of water cycle changes from land-based data because surface observations of rainfall and evaporation were sparse.

Dr Matear said the world’s oceans provided a much clearer picture.

” The ocean matters to climate - it stores 97 per cent of the world’s water; receives 80 per cent of all surface rainfall and; it has absorbed 90 per cent of the Earth’s energy increase associated with past atmospheric warming,” he said.

Dr Matear said the finding had ”significant implications” for urban planning and food security. ”In tropical regions like Queensland, it will affect infrastructure, agriculture and urban planning,” he said

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