Sea level rise is accelerating, confirms study

NASA's GRACE mission used satellites to measure changes in ice mass. This image shows areas of Antarctica that gained or lost ice between 2002 and 2016

Sea level rise is accelerating, confirms study

The end-of-century surge rate would put many low-lying regions of the world at risk of flooding, including coastal cities such as Miami and Shanghai.

But according to a new analysis of satellite data collected over the past 25 years and published this week in the Proceedings of the National Academy of Sciences, that rate is increasing by almost a tenth of a millimeter per year - meaning that by the turn of the next century, the ocean could be continuing to rise at more than three times its current rate.

The team observed a total rise in the ocean of 7 cm in 25 years of data, which aligns with the generally accepted current rate of sea level rise of about 3 mm per year, according to a study released on Monday in the Proceedings of the National Academy of Sciences.

If the trend continues, it is likely to lead to an annual average sea-level rise of at least 1cm per year by 2100.

"And this is nearly certainly a conservative estimate", said lead author Steve Nerem, an aerospace engineer at the University of Colorado, Boulder.

Of the seven centimetres of sea level rise in the past quarter century, about 55 per cent is from warmer water expanding, and the rest is from melting ice.

The result is a "climate-change-driven" acceleration: the amount the sea levels are rising because of the warming caused by manmade global warming. Volcanic eruptions, for example, can create variability: the Mount Pinatubo eruption in 1991 decreased global mean sea levels immediately before the Topex/Poseidon satellite launch.

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Greenland has caused three times more sea-level rise than Antarctica so far, but ice melt on the southern continent is responsible for more of the acceleration.

The researchers used tide gauge data to identify potential errors in the altimeter estimate. "The tide gauge measurements are essential for determining the uncertainty in the GMSL (global mean sea level) acceleration estimate", said co-author Gary Mitchum, USF College of Marine Science.

Nerem aimed to review his findings as more satellite data became available.

In addition to NASA's involvement in missions that make direct sea level observations from space, the agency's Earth science work includes a wide-ranging portfolio of missions, field campaigns and research that contribute to improved understanding of how global sea level is changing.

An Adelie penguin stands atop a block of melting ice near the French station at Dumont díUrville in East Antarctica January 23, 2010.

"This study highlights the important role that can be played by satellite records in validating climate model projections", said John Fasullo, a climate scientist at the National Centre for Atmospheric Research.

The figure calculated by Professor Nerem's study is similar to those predicted by the Intergovernmental Panel on Climate Charge (IPCC) under its upper 8.5 scenario, which assumes increasing greenhouse gas emissions. The 25-year record is just long enough to provide an initial detection of acceleration-the results will become more robust as the Jason-3 and subsequent altimetry satellites lengthen the time series.

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