Sea-level rise since the Industrial Revolution has been faster by natural standards, and - at current rates - may reach 80cm above the modern level by 2100 and 2.5 metres by 2200, a new study has warned.
Researchers from the University of Southampton and the Australian National University used geological evidence of the past few million years to derive a background pattern of natural sea-level rise.
This was compared with historical tide-gauge and satellite observations of sea-level change for the 'global warming' period, since the industrial revolution.
"There is no speculation about any new mechanisms that might develop due to human-made global warming. Put simply, we consider purely what nature has done before, and therefore could do again," lead author Professor Eelco Rohling said.
"Geological data showed that sea level would likely rise by nine metres or more as the climate system adjusts to today's greenhouse effect. But the timescale for this was unclear. So we studied past rates and timescales of sea-level rise, and used these to determine the natural background pattern," co-author Dr Gavin Foster said.
"Historical observations show a rising sea level from about 1800 as sea water warmed up and melt water from glaciers and ice fields flowed into the oceans. Around 2000, sea level was rising by about 3 mm per year. That may sound slow, but it produces a significant change over time," co-author Dr Ivan Haigh added.
The natural background pattern allowed the team to see whether recent sea-level changes are exceptional or within the normal range, and whether they are faster, equal, or slower than natural changes.
"For the first time, we can see that the modern sea-level rise is quite fast by natural standards. Based on our natural background pattern, only about half the observed sea-level rise would be expected," Rohling said.
The study was published in the journal Scientific Reports.
