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New Study Lowers Estimate Of Ancient Sea-Level Rise: 20 To 43 Feet
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NEW YORK, New York -- The seas are creeping higher as the planet warms. But how high will they go? Projections for the year 2100 range from inches to several feet, or more. The sub-tropical islands of Bermuda and the Bahamas contain important sites where researchers have gone looking for answers; by pinpointing where shorelines stood on cliffs and reefs there during an extremely warm period 400,000 years ago, they hope to narrow the range of global sea-level projections for the future.

After correcting for what they say were the sinking of the islands at that time, a new study in the journal Nature estimates the seas rose 20 to 43 feet higher than today—up to a third less than previous estimates, but still a drastic change. The new study infers that Greenland and West Antarctica ice sheets collapsed at that time, but not the even bigger East Antarctic Ice Sheet.

"Our study provides a simple explanation for these high beach deposits," said study lead author Maureen Raymo, a climate scientist at Columbia University's Lamont-Doherty Earth Observatory.

Average global sea level has risen eight inches since the 1880s. It is currently rising an inch per decade, driven by thermal expansion of seawater and melting of glaciers and ice sheets, including the still mostly intact ice sheets of Greenland and West Antarctica. In its most recent report, the Intergovernmental Panel on Climate Change estimated that the seas could rise up to two feet by 2100; but that number could go higher depending on the amount of polar ice melt, and quantity of greenhouse gas emissions by humans. The United Nations estimates that five feet of sea-level rise would be enough to swamp 17 million people in low-lying Bangladesh alone.

The cliffs and ancient reefs on Bermuda and the Bahamas have attracted fossil hunters for decades, and more recently, scientists investigating global sea level. In a 1999 study in the journal Geology, Paul Hearty, a scientist at the University of North Carolina, Wilmington, estimated that during the period 400,000 years ago, the seas rose nearly 70 feet, in between glacial periods. He hypothesized that the East Antarctic ice sheet must have partly melted to produce such a rise. In 2007, University of Hawaii scientist Gary McMurtry offered a competing hypothesis in the journal Sedimentary Geology: that a mega-tsunami generated by a collapsing volcano off the Canary Islands created the high-water mark.

The new study comes up with a different take. It factors in the loading and unloading of ice from North America during the ice ages preceding the sea-level rise. As the ice sheets grew, their weight pushed down the land beneath them, while causing land at the edges of the continent—including Bermuda and the Bahamas--to bulge up, says Raymo. When the ice pulled back, the continent rebounded, and the islands sank.

"Bermuda and the Bahamas are not a pristine measure of the volumes of ice that melted in the past, because they're contaminated by effects left over from the ice ages," said study coauthor Jerry Mitrovica, a geophysicist at Harvard University.

The new study infers that the huge Greenland and West Antarctic ice sheets indeed collapsed at the time, but that loss from the even vaster East Antarctic Ice Sheet was negligible. Today, both Greenland and West Antarctica are losing mass in a warming world, but signals from East Antarctica—about eight times bigger than the other two combined--are less clear. Raymo said the study helps show that "catastrophic collapse" of the East Antarctic ice is probably not a threat today. "However, we do need to worry about Greenland and West Antarctica," she said.

The study's revised estimate of 20 to 43 feet makes sense, said sea-level rise expert Mark Siddall, a climate scientist at the University of Bristol who was not involved in the study. But, he added, it would probably take hundreds to thousands of years for such a rise to occur again. "We're moving from a place of disagreement about sea level estimates from this past period to one consistent theory that reconciles data from diverse geographic areas," he said.

Views expressed in this article do not necessarily reflect those of UnderwaterTimes.com, its staff or its advertisers.

Reader Comments

8 people have commented so far. cloud add your comment

One of the better studies I've seen, the only discord being the "usual" BS about mankind caused warming!! Where is the CO2(oops, sorry we are finally getting off that lie)from man in all these previous high-water marks, how about the tops of Rocky Mountains with seashells and seacreatures, (I know that was possibly from an upheaval or overthrust) the point being that man has little effect on global warming. Of interest here is the island "curl" effect, hadn't seen that previously discussed. Thanks for a great article.
   comment# 1   - Maverick · Eureka USA · Mar 15, 2012 @ 2:40pm

This is all bunk. We are not causing the climate change. The earth and the sun have been doing that for us since time began. This is just the new religion du jour of the liberal left. Twenty years ago it was AIDS research and before that it was radical feminism. It will be something else 5 years from now.
   comment# 2   - Carlos · Brandon, MS · Mar 15, 2012 @ 2:41pm

I lived next to the ocean fpor 15 years and I never nociced the sea level rising. I remember seeing estremely hight tide and extremelly low tide once a month. Storms at sea eroded the seashore, but never rising seas.
   comment# 3   - a p garcia · san benito, tx usa · Mar 15, 2012 @ 3:42pm

This article proves that oil companies are completely blameless and any dramatic recent rise in global temperatures is strictly due to natural causes. Shell and Exxon, please mail the check to my business office!
   comment# 4   - Paid Oil Company Shill · Noshame, Checkplease · Mar 15, 2012 @ 6:09pm

And of course the haarp project by the usn thats warming the upper atmosphere with sites world wide and in space based satelites arent redirecting the weather patterns world wide so they can drill for oil in the arctic and eventually antarctic and if youve been watching lately antarctic snow has iron in it causing algie blooms this was proposed years ago to cure the ozone hole it kills everything with a red tide know you read about that
   comment# 5   - phantom · greenacres · Mar 15, 2012 @ 8:18pm

Sea rise from global warming... heh...heheheh...BWWAAHAHAAHaahaaHAHAHAHHAHAHahahahahah SNORT! Suckers. There is no "global warming other than that cause by solar cycles. Who says so? Over 31,000 scientists and 100,000 years of ice cores, lakebed sediment and tree rings. These scientist back it up with facts, unlike the 1500 at the UN IPCC (about 15 of whom are actually scientists) and those begging for government (read: "taypayer") funds. Here it is: http://www.petitionproject.com/ When are you people ever going to get tired of spreading this manure? Your poopaganda war has failed. You lost. Read the facts, learn them live them, get on with your lives. Those of you claiming that oil companies are buying scientists, well gee. Isn't that what global warmists are doing? How do you think they get the money for all this research? It sure doesn't come out of their pockets. They insist on selling this stuff so that they can get more money from the government to fight it. And you people are their "useful idiots".
   comment# 6   - Dusty · San Bernardino, Ca., USA · Mar 15, 2012 @ 8:31pm

These wierdos cannot forecast the weather 24 hours in advance but they know all about climate activity and the Earths surface changes since before there were anyone to see them unless we have journels from some space visitors who were passing by...right-on
   comment# 7   - Boston Blackie · Swanton, O. · Mar 16, 2012 @ 7:57am

I currently live on the island of Guam. Guam is an extinct volcano rising from the ocean floor about 12000 feet below. A coral reef built up on submerged mountain over millions of years. The reminants of the reef are now hard limestone. The northern end of the island is a plateau of ancient limestone. The ancient water line is about 400-600 feet above the current sea level. I believe that anthropogenic climate disruption will not contribute any significant amount to the continuing rise in sea levels during this interglacial warming period. Humans should be more concerned about what caused the last ice age, and the 19 before that over the past two million years, and when the next one will be.
   comment# 8   - Matt · Guam · Mar 18, 2012 @ 2:53am
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