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| Last Updated:04/12/2018

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Sea level rise getting faster, finds new study

 NEW DELHI: Global sea levels are rising significantly faster than earlier thought, according to a new Harvard study.

The study, co-authored by Carling Hay and Eric Morrow, of the Department of Earth and Planetary Sciences (EPS), shows that previous estimates of global sea-level rise from 1900-1990 had been over-estimated by as much as 30 percent. The report, however, confirms previous estimates of sea-level change since 1990. The net result is that the rate of sea-level change is now found to be increasing more quickly than previously believed. The new work is described in a January 14 paper published in Nature.

"Scientists now believe that most of the world's ice sheets and mountain glaciers are melting in response to rising temperatures." Hay said. "Melting ice sheets cause global mean sea level to rise. Understanding this contribution is critical in a warming world."

Previous estimates had placed sea-level rise at between 1.5 and 1.8 millimeters annually over the 20th century. Hay and Morrow, however, suggest that from 1901 until 1990, the figure was closer to 1.2 millimeters per year. But everyone agrees that global sea level has risen by about 3 millimeters annually since that time, and so the new study points to a larger acceleration in global sea level.

To obtain their improved estimate of 20th century global sea level, Hay and Morrow approached the challenge of estimating sea-level rise from a completely new perspective.

Typically, Hay said, estimates of sea-level rise are created by dividing the world's oceans into sub-regions, and gathering records from tide gauges - essentially yard-sticks used to measure ocean tides - from each area. Using records that contain the most complete data, researchers average them together to create estimates of sea level for each region, then average those rates together to create a global estimate.

"But these simple averages aren't representative of a true global mean value" Hay explained. "Tide gauges are located along coasts, therefore large areas of the ocean aren't being included in these estimates. And the records that do exist commonly have large gaps."

"We know the sea level is changing for a variety of reasons," Hay said. "There are ongoing effects due to the last ice age, heating and expansion of the ocean due to global warming, changes in ocean circulation, and present-day melting of land-ice, all of which result in unique patterns of sea-level change. These processes combine to produce the observed global mean sea-level rise."

"We are looking at all the available sea-level records and trying to say that Greenland has been melting at this rate, the Arctic at this rate, the Antarctic at this rate, etc." she continued. "We then sum these contributions and add in the rate that the oceans are changing due to thermal expansion to estimate a rate of global mean sea-level change."