EcoAlert: Harvard/Princeton Reseach Warns Polar Caps Threatened

6a00d8341bf7f753ef0115717da95a970b.jpg An analysis of the geological record of the Earth's sea level, carried out by scientists at Princeton and Harvard universities used a novel statistical approach that reveals the planet's polar ice sheets are vulnerable to large-scale melting even under moderate global warming scenarios. Such melting would lead to a large and relatively rapid rise in global sea level.

According to the analysis, an additional 2 degrees of global warming could commit the planet to 6 to 9 meters (20 to 30 feet) of long-term sea level rise. This rise would inundate low-lying coastal areas where hundreds of millions of people now reside. It would permanently submerge New Orleans and other parts of southern Louisiana, much of southern Florida and other parts of the U.S. East Coast, much of Bangladesh, and most of the Netherlands, unless unprecedented and expensive coastal protection were undertaken.


While the researchers' findings indicate that such a rise would likely take centuries to complete, if emissions of greenhouse gases are not abated, the planet could be committed during this century to a level of warming sufficient to trigger this outcome.

The last interglacial stage provides a historical analog for futures with a fairly moderate amount of warming; the high sea levels during the stage suggest that significant chunks of major ice sheets could disappear over a period of centuries in such futures.

Previous geological studies of sea level benchmarks such as coral reefs and beaches had shown that, at many localities, local sea levels during the last interglacial stage were higher than today. But local sea levels differ from those in this earlier stage; one major contributing factor is that the changing masses of the ice sheets alter the planet's gravitational field and deform the solid Earth. As a consequence, inferring global sea level from local geological sea level markers requires a geographically broad data set, a model of the physics of sea level, and a means to integrate the two. The study's authors provide all three, integrating the data and the physics with a statistical approach that allows them to assess the probability distribution of past global sea level and its rate of change.

The findings indicate that sea level during the last interglacial stage rose for centuries at least two to three times faster than the recent rate, and that both the Greenland and West Antarctic ice sheet likely shrank significantly and made important contributions to sea level rise. However, the relative timing of temperature change and sea level change during the last interglacial stage is fairly uncertain, so it is not possible to infer from the analysis how long an exposure to peak temperatures during this stage was needed to commit the planet to peak sea levels.

A similar study by a team of scientists from Bristol, Cardiff and Texas A&M universities braved the lions and hyenas of a small East African village to extract microfossils from rocks which have revealed the level of CO2 in the Earth’s atmosphere at the time of the formation of the ice-cap. New carbon dioxide data confirm that formation of the Antarctic ice-cap some 33.5 million years ago was due to declining carbon dioxide in the atmosphere.

Professor Paul Pearson from Cardiff University’s School of Earth and Ocean Sciences, who led the mission to the remote East Africa village of Stakishari said: “About 34 million years ago the Earth experienced a mysterious cooling trend. Glaciers and small ice sheets developed in Antarctica, sea levels fell and temperate forests began to displace tropical-type vegetation in many areas.

“The period culminated in the rapid development of a continental-scale ice sheet on Antarctica, which has been there ever since. We therefore set out to establish whether there was a substantial decline in atmospheric carbon dioxide levels as the Antarctic ice sheet began to grow.”

Co-author Dr Bridget Wade from Texas A&M University Department of Geology and Geophysics added: “This was the biggest climate switch since the extinction of the dinosaurs 65 million years ago. Our study is the first to provide a direct link between the establishment of an ice sheet on Antarctica and atmospheric carbon dioxide levels and therefore confirms the relationship between carbon dioxide levels in the atmosphere and global climate.”

Geologists have long speculated that the formation of the Antarctic ice-cap was caused by a gradually diminishing natural greenhouse effect. The study’s findings, published in Nature online, confirm that atmospheric CO2 started to decline about 34 million years ago, during the period known to geologists as the Eocene – Oligocene climate transition, and that the ice sheet began to form about 33.5 million years ago when CO2 in the atmosphere reached a tipping point of around 760 parts per million.

The team mapped large expanses of bush and wilderness and pieced together the underlying local rock formations using occasional outcrops of rocks and stream beds. Eventually they discovered sediments of the right age near a traditional African village called Stakishari. By assembling a drilling rig and extracting hundreds of meters of samples from under the ground they were able to obtain exactly the piece of Earth's history they had been searching for.

Posted by Casey Kazan from material provided by Princeton University and Bristol University

http://www.bris.ac.uk/news/2009/6546.html

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