Ice cap melting does not cause an even sea-level rise across the globe

Assumptions that the melting of the polar ice caps due to climate change is causing an even rise in sea levels across the globe are incorrect, according to research by US scientists, who have found that melting ice could even lower sea levels in some areas.

The study, published in the 22 February issue of Nature, found that melt-water from different ice caps each have their own unique ‘fingerprint’ of sea level rise, showing a variety of effects throughout different geographical locations. The Antarctic ice-melt, for example, will have a distinctly different pattern in how it affects sea level than melting from Greenland or small mountain glaciers, say the researchers.

“We calculated these fingerprints using computer models and then showed that the observed record of sea level change displays the fingerprints,” said Jerry Mitrovica, University of Toronto Geophysics Professor, and lead author of the report. “Sea level is rising, and based on our work and the analysis of sea level data, not only can we assess the total amount melting from the ice caps, but we can also tell where that melt-water is coming from.”

For example, says Mitrovica, if the entire Greenland ice cap was to melt, the sea level around relatively close coastlines, such as those of Britain and Newfoundland, would actually fall, with southern hemisphere levels rising. If the Antarctic cap was to melt, on the other hand, northern hemisphere sea levels would rise, whilst around countries such as Australia, it would fall.

This unexpected effect is due to the gravitational pull exerted by the ice caps on the sea, which is reduced as the ice sheets themselves become smaller, explain the researchers.

“We’ve really strengthened the link between today’s sea level changes and ice melting and we’ve found a way of unravelling the details of this link,” said Mitrovica. “By doing that, we’ve also strengthened extrapolations being made for the future effect of climate warming. And these extrapolations show continued acceleration of sea level rise late into the present century, leading to more flooding of coastal communities.” On average, says Mitrovica, sea levels are currently rising at a rate of 1.8 mm per year.

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