Sea levels rising at fast rate, studies show

Damian Carrington

SEA levels are rising several times faster than they have in the past 2,800 years, with the process accelerating because of manmade global warming, according to new studies. An international team of scientists examined two-dozen locations across the globe to chart rising and falling seas over centuries and millennia.
Until the 1880s and the world’s industrialisation, the fastest seas rose was about 3cm to 4cm a century. During that time global sea levels did not get much higher or lower than 7.6cm above or below the 2,000-year average. But in the 20th century the world’s seas rose 14cm. Two different studies published on Monday in the journal Proceedings of the National Academy of Sciences said that by 2100 the world’s oceans would rise between 28cm to 131cm, depending on how much heat-trapping gas Earth’s industries and vehicles expel. Rutgers earth and planetary sciences professor Bob Kopp, lead author of the study, which looked back at sea levels over the past three millennia, said: “There’s no question that the 20th century is the fastest. “It’s because of the temperature increase in the 20th century which has been driven by fossil fuel use.”
Sea level rise in the 20th century was mostly manmade, the study authors said. A separate, not-yet-published study by Kopp and others found that since 1950 about two-thirds of the US coastal floods in 27 locales were linked to manmade warming. Study co-author Stefan Rahmstorf, of the Potsdam Institute for Climate Impact Research in Germany, said that if seas continued to rise as projected, another 45cm would cause lots of problems and expense, especially with surges during storms. “There is such a tight relationship between sea level and temperature,” Horton said. “I wish there wasn’t, then we wouldn’t be as worried.” Huge sea-level rises caused by climate change will last far longer than the entire history of human civilisation to date, according to new research, unless the brief window of opportunity of the next few decades is used to cut carbon emissions drastically. Even if global warming is capped at governments’ target of 2C – which is already seen as difficult – 20% of the world’s population will eventually have to migrate away from coasts swamped by rising oceans. Cities including New York, London, Rio de Janeiro, Cairo, Calcutta, Jakarta and Shanghai would all be submerged.
By far the greatest contributor to the sea level rise – about 80% – would be the melting of the Antarctic ice sheet. Another new study in Nature Climate Change published on Monday reveals that some large Antarctic ice sheets are dangerously close to losing the sea ice shelves that hold back their flow into the ocean. Huge floating sea ice shelves around Antarctica provide buttresses for the glaciers and ice sheets on the continent. But when they are lost to melting, as happened the with Larsen B shelf in 2002, the speed of flow into the ocean can increase eightfold.
If greenhouse gas pollution continues at the current pace, both studies project increases of about 57cm to 131cm. If countries fulfil the treaty agreed upon last year in Paris and limit further warming to another 2F, sea level rise would be in the 28 to 56cm range. Jonathan Overpeck at the University of Arizona, who wasn’t part of the studies, praised them, saying they show a clear cause and effect between warming and sea level rise.
— Courtesy: The Guardian

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