Another great flood? (article on results of melting ice sheets)

Here is a recent article saying that flooding caused by melting antarctic ice sheets may cause more higher ocean water levels than previously thought, good to take note if you live in a coastal city like I do. or New York.

More of North America may face flooding from Antarctic ice sheet melt: study

Thu Feb 5, 3:02 PM

By Alison Auld, The Canadian Press
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Cities on the east and west coasts of North America will face even greater flooding if a massive Antarctic sheet melts completely, according to a new study that claims the rate of sea level rise is higher than previously thought.

The report, to be published Friday in the journal Science, finds the current estimate of global sea rise is inaccurate because it doesn’t consider three geophysical factors if the West Antarctic ice sheet melts.

The paper states that the average estimate of a five-metre sea level rise should actually go up to seven metres.

The seemingly small difference could submerge much of southern Florida, San Francisco, New York and Washington, D.C., while inundating parts of New Brunswick, Nova Scotia, P.E.I. and British Columbia with water.

“If the West Antarctic ice sheet completely collapses, the U.S. and Canadian coasts will be inundated by six to seven metres of additional water, not five metres as people previously thought,” said Jerry Mitrovica, a geophysicist at the University of Toronto, who co-wrote the report.

“So that’s a lot of excess water on coastal sites that have a lot of population.”

The research finds that the sea level rise would be 30 per cent higher in San Francisco and about 25 per cent higher in Washington, while Tokyo would experience a sea level rise almost 20 per cent greater than thought earlier.

Communities on Canada’s coasts would likely see an increase in excess of six metres.

The scientists said the previous estimate, which is supported by the renowned Intergovernmental Panel on Climate Change, is too simplistic because it doesn’t include several natural effects.

Mitrovica said there is a gravitational pull on the ocean when an ice sheet melts, which in this case would push water away from the sheet and toward the North American continent.

More water would also be pushed north if the ice sheet melts and fills a depression on the Antarctic bedrock that supports the large swath of ice.

The melt would also cause the Earth’s rotation axis to shift dramatically and cause water to move away from the southern Atlantic and Pacific oceans toward North America and the Indian Ocean, the report says.

The West Antarctic ice sheet towers 1,800 metres above sea level, has a volume of water 100 times the amount in all the Great Lakes and is roughly the size of Ontario.

It’s not clear how quickly the sheet is melting, but over the last 100 years the average sea level rise has been two millimetres a year, something Mitrovica said is likely now 50 per cent higher.

Peter Clark, a professor of geoscience at Oregon State University, said no one knows how quickly or if the entire ice sheet will melt, but warns that policy makers should use the new data in their planning.

Aside from flooding, he said a dramatic melt would cause higher rates of coastal erosion, greater damage from major storm events and problems with ground water salinization.

“Many coastal areas need to plan for greater sea level rise than they may have expected,” said Clark, who co-authored the report.

The danger with the West Antarctic sheet is that it’s largely submerged and is exposed to a warming ocean, which leaves it more prone to collapsing due to climate change.

The faster the water warms, the greater risk the ice sheet will collapse. And Mitrovica says the effects will not be uniform around the world, with some regions being hit harder by the increased rate.

The sea level rise would also likely be affected by what happens in other areas, like the Greenland ice sheet and mountain glaciers, which could add to the rate of increase.

“This is only part of the story, but it’s enough of a story to alert people,” Mitrovica said.