Climate change: Earthquake 'hack' reveals scale of ocean warming
Scientists have found a clever new way of measuring ocean warming, using sound waves from undersea earthquakes.
The researchers say the "hack" works because sound travels faster in warmer water.
The team looked at sonic data from the Indian Ocean emitted by tremors over a 10-year period.
As the seas have warmed due to global heating, the scientists have seen the sound waves increase in speed.
Their new method shows the decadal warming trend in the Indian Ocean was far higher than previous estimates.
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The scientists examined data from over 4,000 tremors that occurred in the Indian Ocean between 2004 and 2016.
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The team then looked for pairs of "repeaters", earthquakes with almost identical origins and power.
By measuring how long these slow-moving signals took to travel across the waters from Indonesia to a monitoring station on the island of Diego Garcia, they were able to work out the changes in temperature for the whole of the ocean over the 10-year period.
"It takes sound waves about half an hour to travel from Sumatra to Diego Garcia," lead author Dr Wenbo Wu from the California Institute of Technology told BBC News.
"The temperature change of the deep ocean between Sumatra and Diego Garcia causes this half-hour travel time to vary by a few tenths of a second.
"Because we can measure these variations very accurately, we can infer the small changes in the average temperature of the deep ocean, in this case about a tenth of a degree."
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In their research, the scientists showed that warming in the Indian Ocean over the decade that they studied was greater than previously estimated.
However, the paper has some important caveats.
"It is important to emphasise that this is a result that applies to this particular region and this particular decade," said Dr Wu.
"We need to apply our method in many more regions and over different time frames to evaluate whether there is any systematic under- or over-estimation of the deep-ocean trend globally.
"It is much too early to draw any conclusions in this direction."
https://www.bbc.com/news/science-environment-54193334