Australasian Science: Australia's authority on science since 1938

Salinity Changes Confirm Warming

By Stephen Luntz

Variations in salinity are intensifying, indicating that the Earth’s cycle of evaporation and rainfall has pumped up during the 20th century.

A study of ocean salinity in the American Journal of Climate confirms that variations in salinity are intensifying, indicating that the Earth’s cycle of evaporation and rainfall has pumped up during the 20th century.

As part of his PhD at CSIRO and the University of Tasmania’s joint Quantitative Marine Science Program, Paul Durack compared salinity and temperature recordings from ARGO floats (AS, August 2008, p.14) with mid-20th century data obtained from research vessels. He found that the ocean has become fresher in areas where rainfall is greater than evaporation, while enhanced salinity occurs where evaporation dominates. This is what would be expected if both evaporation and rainfall have increased over time, which is expected as global surface temperatures increase.

“It’s further confirmation from the global ocean that the Earth’s water cycle has accelerated,” says Durack. “These broad-scale patterns of change are qualitatively consistent with simulations reported by the Intergovernmental Panel on Climate Change – wet gets wetter, dry gets drier.”

The pre-ARGO data are too sparse when used alone for detailed regional comparisons of salinity changes, but the new ARGO results indicate that tropical and polar regions are becoming less salty while subtropical and temperate waters are experiencing increased salinity.

Although the results are expected, they’re worrying news. They confirm global warming, and the effects will spill onto land. Areas with plenty of rainfall will tend to get wetter while those that are drought-prone like Australia will become drier.

Durack says that it may be possible to use these new estimates of salinity changes to gain a better understanding of the rate of climate change that has occurred in the 20th century. Further digging may reveal evidence of changes to the oceans’ density gradient, which is the key driver of the global thermohaline circulation (AS, October 2007 p.8).

Studies such as this were one of the reasons for the creation of the ARGO program, and Durack says that two other recent studies have reached the same conclusion. However, he says that his work provides more quantitative assessments of past changes.