The assumption that melting ice caps will flood coastal locations evenly has been dispelled by researchers at the University of Toronto.
Geophysics professor Jerry Mitrovica argues that melting from the Antarctic will have a different affect on sea level than melting from Greenland or small mountain glaciers.
Mitrovica's research paper, published in last week's edition of Nature, begins to answer a question that has long challenged scientists: Why does sea level change vary widely from one geographic location to another, even after these rates have been corrected for known effects.
Mitrovica conducted the research with Mark Tamisiea, a University of Toronto post-doctoral fellow and second author on the paper, James Davis of the Harvard Smithsonian Center for Astrophysics, and Glenn Milne of the University of Durham.
The researchers say their paper provides the sea level "fingerprints" of polar ice sheet melting to prove global climate change is directly affecting the Earth's sea level.
"We calculated these fingerprints using computer models and then showed that the observed record of sea level change displays the fingerprints," said Mitrovica.
"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 meltwater is coming from.
People have been puzzled by the significant variations in sea levels in different parts of the world. Like throwing water in a bathtub, many scientists assumed that if polar ice melting were contributing to sea level rise, it would present itself evenly and uniformly across the Earth's oceans.
Not so, said Mitrovica.
"If the entire Greenland ice cap melted, then places relatively close by, like Britain and Newfoundland, would actually see sea levels fall," he said. "The reason is fairly simple: despite its small size, the Greenland ice sheet exerts a strong gravitational pull on the seas. As the polar sheet melts, it will exert less pull, resulting in lower - not higher - sea levels around Greenland.
"Of course, sea levels will rise on average, and as the meltwater moves away from Greenland it will create problems for countries in the Southern Hemisphere. In the same way, melting from the Antarctic will raise sea levels in the Northern Hemisphere, but not in places like Australia."
Mitrovica and his colleagues backed up their ideas by re-examining data from tide gauges that measure sea level. They found that they could fit nearly all the geographic variations in sea level that they saw in these tide gauges using the distinct sea level patterns they predicted for the melting of polar ice sheets.
It is estimated that sea levels are rising, on average, by about 1.8 millimeters per year.