Featured Research

from universities, journals, and other organizations

New study lowers estimate of ancient sea-level rise

Date:
March 14, 2012
Source:
The Earth Institute at Columbia University
Summary:
The seas are creeping higher as the planet warms. But how high will they go? In Bermuda and the Bahamas, researchers have gone looking for answers; By pinpointing where shorelines stood during a warm period 400,000 years ago, they hope to narrow the range of projections. After correcting for apparent sinking of the islands, the authors of a new study estimate the seas rose 20 to 43 feet higher than today -- far less than previous estimates, but still drastic.

Scientists offer a new explanation for why ancient beach deposits on these cliff tops in Eleuthera, Bahamas, are nearly 70 feet above present day sea level.
Credit: Paul Hearty

The seas are creeping higher as the planet warms, but scientists have not yet reached a consensus about how high they may 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.

Related Articles


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; another just released report says 3.7 million Americans could be threatened by flooding in coming decades.

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. The idea became contentious, since scientists could find little evidence that the ice had indeed gone away at this time. In 2007, University of Hawaii scientist Gary McMurtry offered a competing hypothesis: 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.

This year summer, Raymo and other researchers will bolster their data on ancient sea levels by sampling old shorelines in South Africa and Kenya. In the fall, they will continue work along the U.S. east coast, working from North Carolina to Florida.


Story Source:

The above story is based on materials provided by The Earth Institute at Columbia University. Note: Materials may be edited for content and length.


Journal Reference:

  1. Maureen E. Raymo, Jerry X. Mitrovica. Collapse of polar ice sheets during the stage 11 interglacial. Nature, 2012; DOI: 10.1038/nature10891

Cite This Page:

The Earth Institute at Columbia University. "New study lowers estimate of ancient sea-level rise." ScienceDaily. ScienceDaily, 14 March 2012. <www.sciencedaily.com/releases/2012/03/120314142835.htm>.
The Earth Institute at Columbia University. (2012, March 14). New study lowers estimate of ancient sea-level rise. ScienceDaily. Retrieved November 26, 2014 from www.sciencedaily.com/releases/2012/03/120314142835.htm
The Earth Institute at Columbia University. "New study lowers estimate of ancient sea-level rise." ScienceDaily. www.sciencedaily.com/releases/2012/03/120314142835.htm (accessed November 26, 2014).

Share This


More From ScienceDaily



More Earth & Climate News

Wednesday, November 26, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Antarctic Sea Ice Mystery Thickens... Literally

Antarctic Sea Ice Mystery Thickens... Literally

Newsy (Nov. 25, 2014) — Antarctic sea ice isn't only expanding, it's thicker than previously thought, and scientists aren't sure exactly why. Video provided by Newsy
Powered by NewsLook.com
3D Map of Antarctic Sea Ice to Shed Light on Climate Change

3D Map of Antarctic Sea Ice to Shed Light on Climate Change

Reuters - Innovations Video Online (Nov. 24, 2014) — A multinational group of scientists have released the first ever detailed, high-resolution 3-D maps of Antarctic sea ice. Using an underwater robot equipped with sonar, the researchers mapped the underside of a massive area of sea ice to gauge the impact of climate change. Ben Gruber reports. Video provided by Reuters
Powered by NewsLook.com
Car Park Solution for Flexible Green Energy

Car Park Solution for Flexible Green Energy

Reuters - Innovations Video Online (Nov. 24, 2014) — A British solar power start-up says that by covering millions of existing car park spaces around the UK with flexible solar panels, the country's power problems could be solved. Suzannah Butcher reports. Video provided by Reuters
Powered by NewsLook.com
Yellow-Spotted Turtles Rescued from Trafficking

Yellow-Spotted Turtles Rescued from Trafficking

Reuters - Light News Video Online (Nov. 24, 2014) — Hundreds of Amazon River turtles released into the wild in Peru. Sharon Reich reports. Video provided by Reuters
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins