London: A new study has recently revealed global oceans have risen at almost double the estimate in the last two decades than previously thought.
Their reassessment of tide gauge data from 1900-1990 found that the world's seas went up more slowly than earlier estimates - by about 1.2mm per year, but this makes the 3mm per year tracked by satellites since 1990 a much bigger trend change as a consequence, the BBC reported.
Dr Carling Hay from Harvard University in Cambridge, Massachusetts, said that this new acceleration was about 25 percent higher than previous estimates.
The data needs careful handling because it hides all kinds of "contamination". Scientists must account for effects that mask the true signal; such as tectonic movements that might force the local land upwards - and those that exaggerate it; such as groundwater extraction, which will make the land dip.
Attention needs to be paid also to natural oscillations in ocean behavior, which can make waters rise and fall on decadal timescales.
It could mean some projections for future rises having to be revisited.
The modern tide gauge is now a highly sophisticated tool. Coastal instruments have recorded sea level change at some locations for more than 200 yearsn the last IPCC report, global mean sea-level rise for 2081-2100 was projected to be between 26cm (at the low end) and 82cm (at the high end), depending on the greenhouse emissions path this century.