To Measure Sea Level Rise, Weigh the Ocean

Getting an accurate measure of the rise in worldwide sea level is more difficult than you might expect, thanks to a host of complicating factors like regional weather and warming and seasonal changes in ocean mass.

To get around these obstacles, British researchers have proposed a new way of calculating sea level rise: weighing the ocean. But not the whole thing — just a segment of it, in the tropical Pacific.

In a study published Sept. 1 in the journal Geophysical Research Letters, the scientists found that this area of the ocean is "quiet" and its mass stays constant year-round. Computer models suggest its weight could be used as a steadfast representative to estimate the world's ocean mass and sea level.

"The principle is rather like watching your bath fill: you don't look near the taps, where all you can see is splashing and swirling, you look at the other end where the rise is slow and steady," Christopher Hughes, study author and National Oceanography Centre researcher, said in a statement.

The scientists envision placing a pressure gauge on the ocean floor to calculate the weight of the water above. Currently, however, such a device doesn't exist. But the researchers think the first researcher to develop such an instrument "will have solved the biggest measurement problem in sea level science, and produced an instrument of enormous value in other branches of oceanography," Hughes said.

All of the oceans on Earth are estimated to have a volume of 0.3 billion cubic miles (1.332 billion cubic kilometers) and an average depth of 12,081 feet (3,682 meters).

Global sea levels are rising about 0.1 inches (3 millimeters) per year, but predictions of sea rise over the century vary from 1 foot (30 centimeters) to over 3 feet (1 m), according to the release.

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