Scientists warns oceans may rise over a metre by 2100, five metres by 2300

(AFP)
Oceans are likely to rise the maximum amount as 1.3 metres by 2100 if surface warms another 3.5 degrees Celsius, scientists warned Friday.

By 2300, when ice sheets covering West Antarctica and Greenland will have shed trillions of tonnes in mass, sea levels could go up by quite five metres thereunder temperature scenario, redrawing the planet's coastlines, they reported during a peer-reviewed survey of quite 100 leading experts.

About one-tenth of the world's population, or 770 million people, today survive land but five metres above the high water line.

Even if the Paris climate treaty goal of capping heating below 2C is met -- a really big "if" -- the ocean watermark could go up two metres by 2300, consistent with a study within the journal Climate Atmospheric Science.





Earth's average surface temperature has risen just over one degree Centigrade since the pre-industrial era, a widely used benchmark for measuring heating .

"It is obvious now that previous sea-level rise estimates are too low," co-author Stefan Rahmstorf, head of Earth system analysis at the Potsdam Institute for Climate Impact Research (PIK), told AFP.

The new projections for both the 2100 and 2300 horizons are significantly above those from the UN Intergovernmental Panel on global climate change (IPCC), including a special report on oceans it released in September.

"The IPCC tends to be very cautious and conservative, which is why it had to correct itself upwards already several times," Rahmstorf said.





- Ice sheets the most driver -

Sea-level projections within the IPCC's landmark 2014 Assessment Report were 60 percent above those within the previous edition, he noted. a replacement Assessment are going to be finalised by the top of next year.

While less visible than climate-enhanced hurricanes or persistent drought, water level rise may ultimately prove the foremost devastating of worldwide warming impacts.

Indeed, it's the additional centimetres of ocean water that make storm surges from ever-stronger tropical cyclones such a lot more deadly and destructive, experts say.

Benjamin Horton, acting chair of the Nanyang Technical University's Asian School of the Environment in Singapore, led the survey to offer "policymakers an summary of the state of the science", a press release said.

Across the 20th century, water level rise was caused mainly by melting glaciers and therefore the expansion of ocean water because it warms.





But over the last 20 years the most driver has become the melting and disintegrating of Earth's two ice sheets.

Greenland and West Antarctica are shedding a minimum of sixfold more ice today than during the 1990s. From 1992 through 2017 they lost some 6.4 trillion tonnes in mass.

Over the last decade, the ocean level has gone up about four millimetres per annum . getting into the 22nd century, however, the waterline could rise ten times faster, even under an optimistic greenhouse emission emissions scenario, the IPCC has said.

The Greenland and West Antarctic ice sheets hold enough frozen water to lift oceans about 13 metres. East Antarctica, which is more stable, holds another 50 metres' worth.

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