Naked Science Forum
Life Sciences => The Environment => Topic started by: simonm on 22/06/2009 13:30:24
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Hi
I would be grateful for a bit of peer review of a few thoughts on sea level increase based on meltwater from Greenland. I've expanded on this on my own blog: http://solarkent.wordpress.com/2009/06/18/uk-climate-sea-level-rise/ but in summary:
The mass of ice on Greenland goes some part to define where the centre of gravity is on the Earth (A sphere hanging in space subject to its own gravity- okay I know we are orbiting etc.) As this ice melts, surely it will remain as a mass of water with its highest point in the region of Greenland, effectively very slightly re-shaping the sphere but retaining the centre of gravity where it is. To assume it will flow in some way towards the Pacific seems to assume that the work is flat.
So, when talking about average sea level increase due to the Greenland ice melt, surely we should calculate this based on the increase remaining local to Greenland.
This implies that the North American Eastern Coast is at greater risk, also Europe but to a lesser extent!
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Typo above: To assume it will flow in some way towards the Pacific seems to assume that the world [:D] is flat.
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You need to remember that the Earth isn't a sphere but, due to its spin, bulges around the equator and is flattened at the poles. Thus, although Mt. Everest is 8848 metres above sea-level, it's about 2400 meters closer to the center of the Earth than Mt. Chimborazo in Ecuador, which is actually the furthest point from the Earth's center and so perhaps should really be considered to be the highest point on Earth.
The melt water from Greenland will also be subject to this centripetal force, resulting from the Earth's spin, and being highly mobile will, as a consequence, be 'thrown' outwards, and in effect, downwards towards the Earth's equator.
Depending upon how accurate you want to be, you might also want to take local gravitational variations into account too, as these will affect water levels too (up to, at a guess, perhaps a foot or so).
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Just to add to what Lee has already said: There was a piece about this on NPR not too long ago...(this refers to the west antartic ice sheet, not greenland though)
http://www.npr.org/templates/story/story.php?storyId=104133389
Morning Edition, May 15, 2009 · Scientists have been worried about the West Antarctic Ice Sheet for decades. A new study finds that if it were to collapse, global sea level would rise drastically, though not as much as predicted 30 years ago.
Much of the West Antarctic Ice Sheet is vulnerable because it rests on ground below sea level. If warm ocean water gets under it, the ice could start flowing off the continent and into the sea. That ice, and ultimately water, would increase sea levels by a substantial amount. A landmark research paper published 30 years ago concluded that the ice sheet contains enough water to raise global sea level by 20 feet.
"The strange thing about that study is that nobody has really reevaluated the number since then," says Jonathan Bamber, from the University of Bristol in the U.K.
In a study published Thursday in Science magazine, Bamber's group now concludes that if West Antarctica does collapse catastrophically, global sea level would eventually rise by about 11 feet, not 20.
Bamber and his colleagues used new data about Antarctica's geology and were able to refine how much of the ice sheet is actually vulnerable to a runaway collapse. Using radar and gravity data, they have a much better idea of the shape of the ice cap — and the shape of the rock below.
"And what we found was that it's not the whole of West Antarctica. It's about 70 percent of the area that would melt away into the ocean, according to this hypothesis."
But, sea level doesn't go up the same everywhere. The West Antarctic ice sheet weighs a lot, and that mass creates a gravitational pull that currently piles up ocean water in the southern ocean. If the ice sheet melts, the earth's gravity field will shift and water will flow north. So sea level will rise more on some coastlines, less on others, says Bamber. Still, coastal cities around the world would gradually find themselves under water.
"Global sea level rise is 11 feet. But in some places, it's about 25 percent more than that," he says. "And unfortunately it looks like the Pacific and Atlantic seaboards, of North America at least, are areas where the relative change in sea level is going to be greatest."
A Changing Coastline
So in the long run, U.S. shorelines could retreat more than coastlines elsewhere. But that's the long run, and Bamberg says the "$64 million question" is: How much of sea level rise could occur in the coming decades?
And Bamber has no answer. Neither does any other glaciologist, including Robert Bindschadler at NASA's Goddard Space Flight Center. But what Bindschadler does say is he doesn't want the new research on the long-term fate of the ice sheet to distract people from the more immediate worries.
"Because it really doesn't change the picture. Decision-makers, the public, they have to worry about this century, or maybe if they're really visionary, the next century. This paper doesn't change that picture one iota."
If the West Antarctic Ice Sheet does collapse, it is likely to take hundreds and hundreds of years. And Bindschadler says the global changes in gravity, which would redistribute ocean water around the world, would take even longer.
"Those won't come into play for many centuries, if not millennia down the road," he says.
Small Changes Could Have Big Impact
And even then, Bindschadler can think of scenarios in which the West Antarctic Ice Sheet could still melt entirely away and still raise global sea level by 20 feet.
Twenty feet or 11 feet, Bamber says, in either case, we can't breathe easy.
"Seventeen million people in Bangladesh alone would be displaced for about a 4-foot sea level rise. So, yeah, 11 feet is just unthinkable," Bamber says.
There are signs that we could be heading gradually in that direction. Two large streams of ice that flow from the Antarctic continent into the ocean have been speeding up for the past few years. Scientists are wondering if this could be the first
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Thanks Paul. This has some pretty interesting ramifications for late Pleistocene/early Holocene melt water pulses from the Laurentide ice sheet and through the St Lawrence estuary (such as the Elder and Younger Dryas, 9.1, and 8.2 ka events). If a freshwater lens were to stay in residence for an extended period of time, the MOC could be greatly affected even though the release of water might happen very quickly.
Ill have to look up the paper!
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Ill have to look up the paper!
Let us know what you think
Here is a link from a twitter account I follow, I have previously linked to main site.
Follow Ocean Trends From Your Desktop With NASA's Sea Level Viewer
http://www.earthtoday.net/news/viewpr.rss.html?pid=28479
Heat from the oceans is a driving force of climate, and the best place to watch ocean heat circulate is from space. Now Internet users can access these data by using the Sea Level Viewer, an interactive visualization tool developed at NASA's Jet Propulsion Laboratory (JPL), Pasadena, Calif.
"Sea level is an important type of climate data, already used by many scientists," said Randal Jackson, who produces NASA's Global Climate Change website out of NASA JPL. "Our goal was to present it in a form that's visual, interactive and accessible to the general public."
Since 1992 NASA and the French space agency CNES have operated satellites that measure the precise height of Earth's oceans. In 1992, TOPEX/Poseidon launched and it was followed by the Jason-1 satellite, launched in 2001. The Ocean Surface Topography Mission on the Jason-2 satellite launched in June 2008, as a follow-on mission to Jason-1. The sea level height reflects the amount of heat stored in the water which is extremely important in hurricane forecasting.
The NASA Sea Level Viewer provides users with an up-to-date look at recent ocean topography data, allowing them to explore a global view or watch videos explaining the impact of sea surface height on Earth's climate. The Sea Level Viewer is accessible through NASA's Global Climate Change website, http://climate.jpl.nasa.gov.
On the Sea Level Viewer webpage, click on the "current" button to see a recent map of sea level data as collected by the Jason-1 and Jason-2 satellites. The data are presented on a revolving globe, with clickable hot spots that explain recent trends. In the global view, white areas represent sea surface heights between 8 and 24 centimeters (3.1 to 9.4 inches) above normal, indicating warmer, expanded water. Dark areas represent sea surface heights between 8 and 24 centimeters below normal, indicating cooler water.
Users can also click to learn about noteworthy sea level phenomena in recent years, such as the extraordinary El Nino of 1997-1998, which played havoc with normal climate patterns. Other features include 2005's Hurricane Katrina, 2004's Indian Ocean tsunami, and 1999's La Nina event. There's also information on how space-based observations are helping forecasters predict the strength and intensity of hurricanes.
NASA Flash 'Sea Level Viewer'
http://climate.jpl.nasa.gov/SeaLevelViewer/seaLevelViewer.cfm