March 15, 2012
Evidence In Bahamas And Bermuda Suggests Increased Rise In Sea Levels
Scientists are now predicting sea levels will climb another several inches -- or even a few feet -- by the year 2100, according to recent studies.
Studying cliffs and ancient reefs on the sub-tropical islands of the Bahamas and Bermuda, scientists are investigating global sea rise and comparing these results against data from more than a century ago.
The Bahamas and Bermuda have been attracting fossil hunters for many years. The land on the Bahamas, for example, is built on a foundation of fossil coral and disintegrated coral reefs and seashells. Scientists are able to use clues and data from this ancient ground to understand how much and how fast sea levels rose during a warm period more than 400,000 years ago. Using this data, the scientists hope to predict global sea-levels for the future.
These scientists believe that the sub-tropical islands actually sank lower during this warm period, but after accounting for this phenomenon, it is estimated that the sea-levels rose 20 to 43 feet higher than originally estimated. This is a third less than originally estimated, but a drastic change nonetheless.
The cause of this rise in sea levels? Scientists believe that ice sheets in Greenland and West Antarctica collapsed during this warm period. They also believe that vast ice sheets from East Antarctica also melted into the sea, though this ice loss was negligible.
“Our research provides a simple explanation for high beach deposits [such as fossils in the Bahamas],” said the paper´s lead author Maureen Raymo, a scientist at Columbia University´s Lamont-Doherty Earth Observatory.
Global sea-levels have risen eight inches since the 1880´s and continue to rise at the rate of an inch per decade. Thermal expansion of seawater and melting of ice sheets and glaciers are the cause of this slow and steady rise. Ice sheets in Greenland and West Antarctica remain largely intact, although they are contributing to the rise in sea-levels.
A recent report by the Intergovernmental Panel on Climate Change (IPCC) suggests that sea-levels could rise by 2 feet by the year 2100. This number could be higher depending on ice melts and greenhouse gasses. Should the sea rise more than 5 feet, scientists predict that more than 17 million people could be affected in Bangladesh alone.
The new study also factors in the loading and unloading of ice from North America during the ice ages, according to the National Science Foundation.
As these ice sheets grew they pushed the land beneath them down under their weight. This force caused islands such as the Bahamas and Bermuda to raise upward. When the ice sank again, the continents and islands returned to their original levels.
“We´re re-thinking many of our estimates of past sea-level rise now that we´re more aware of the effects of unloading of ice,” said Bil Haq, program director in the National Science Foundation´s (NSF) Division of Ocean Sciences, which funded the research. “We now have a meaningful way of calculating the rebound.
“This study is a good example of collaboration between paleoceanography and geophysics to resolve an important issue: the question of future sea-level rise.”
While scientists are not yet concerned about the ice sheets in East Antarctica, they are worried about the ice sheets in Greenland and West Antarctica.
The results of this study were published in this week´s issue of the journal Nature.
Image Caption: New explanation for why beach deposits in the Bahamas are 70 feet above sea level. Credit: Paul Hearty