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A new analysis suggests that meltwater from continental ice, rather than ocean warming, could be the main factor behind the current global sea-level rise that is being linked to climate change, and sheds light on inconsistencies in past estimates.

The rate at which the oceans are rising as a result of global warming has been a bone of contention in the climate change community for many years. Direct measurements from tide gauges put the rate of sea-level rise at 1.5-2.0 millimetres per year during the twentieth century.

In the past, most of this rise had been thought to result from ocean warming, with the rest due to the melting of continental ice. But more recent (indirect) estimates of these components fall far short of this total, casting doubt on earlier figures.

In this week's issue of Nature, US scientists Laury Miller and Bruce C. Douglas report that data from gauges in the Pacific and Atlantic oceans, and spanning more than 90 years, supports the original observations.

The authors reject previous claims that tidal gauges are inaccurate because they happen to be located in areas of abnormally high ocean warming. They conclude that their findings provide "clear evidence" that it is an increase in mass — rather than expansion owing to ocean warming — that plays a "dominant role" in twentieth-century global sea level rise.

This, they say, supports the theory that more than half of the rise in sea levels is attributable to freshwater from melting continental ice.

Link to research paper in Nature

Reference: Nature 428, 406 (2004)