Sea levels on earth are rising several times faster than they have in the past 2800 years and are accelerating because of man-made global warming, according to new studies.
An international team of scientists dug into two dozen locations across the globe to chart gently rising and falling seas over centuries and millennia.
Until the 1880s and the world’s industrialisation, the fastest seas rose was about 3 to 4 centimetres a century, plus or minus a bit. During that time global sea level really didn’t get much higher or lower than 7.5cm above or below the 2000-year average.
But in the 20th century the world’s seas rose 14cm. Since 1993 the rate has soared to 30cm per century.
And two different studies published on Monday in the journal Proceedings of the National Academy of Sciences, said that by 2100 the world’s oceans will rise between 28cm to 131cm, depending on how much heat-trapping gas earth’s industries and vehicles expel.
‘There’s no question that the 20th century is the fastest’, said Rutgers earth and planetary sciences professor Bob Kopp, lead author of the study that looked back at sea levels over the past three millennia.
‘It’s because of the temperature increase in the 20th century which has been driven by fossil fuel use.’
To figure out past sea levels and rates of rise and fall, scientists engaged in a ‘geological detective story’, said study co-author Ben Horton, a Rutgers marine scientist. They went around the world looking at salt marshes and other coastal locations and used different clues to figure out what the sea level was at different times.
On top of that they checked their figures by easy markers such as the rise of lead with the start of the industrial age and isotopes only seen in the atomic age.
When Kopp and colleagues charted the sea level rise over the centuries – they went back 3,000 years, but are not confident in the most distant 200 years – they saw earth’s sea level was on a downward trend until the industrial age.
Sea level rise in the 20th century is mostly man-made, the study authors said. A separate, not-yet-published study by Kopp and others found since 1950, about two-thirds of the US nuisance coastal floods in 27 locales have the fingerprints of man-made warming.
And if seas continue to rise, as projected, another 45cm of sea level rise is going to cause lots of problems and expense, especially with surge during storms, said study co-author Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research in Germany.
The link to temperature is basic science, the study’s authors said. Warm water expands. Cold water contracts.