June 21, 2011

Increasing Temperatures Linked To Rapid Sea Level Rise

A consistent link exists between changes in global mean surface temperature and sea level, resulting in a greater rate of sea-level rise along the U.S. Atlantic coast than that of the past 2,000 years, says an international research team.

"Sea-level rise is a potentially disastrous outcome of climate change, as rising temperatures melt land-based iced and warm ocean waters," says Benjamin Horton, associate professor and director of the Sea Level Research Laboratory at the University of Pennsylvania.

Horton and Andrew Kemp, fellow postdoctoral now at Yale University's Climate and Energy Institute conducted the research which was published in the journal Proceedings of the National Academy of Sciences on June 20.

The team constructed a new 2,000-year history of seal level elevations, which will help scientists refine the models currently used to predict climate-change-induced sea level rise.

"Scenarios of future rise are dependent upon understanding the response of sea level to climate changes," Kemp says. "Accurate estimates of past sea-level variability provide a context for such projections."

Michael E. Mann, professor of meteorology at Pennsylvania State University says, "One of the largest uncertainties in projecting the impacts of climate change involves predicting the amount and rate of future sea level rise."

"The societal ramifications are as great as any climate change impact, but, because the uncertainties are particularly large due to limitations in the representations of some key processes, such as ice sheet collapse, in existing models, we still do not know how sea level will rise."

In order to create the sea level timeline, sediment cores from salt marshes in North Carolina were examined. From the data, an unbroken record of sea level through time was created.

The remains of foraminifera, tiny plankton-like creatures that live in the oceans, were used to determine sea level. Different species of foraminifera live at different depths in the oceans, therefore a survey of the types of remains will give researchers the knowledge of how deep the ocean was in that particular spot at the time the sediment layer was laid down.

A timeline of the sea level changes comes from the careful dating of the layers provided, the study says.

By combining the sea level changes through time with the already established temperature record for the past 1,000 years, researchers were able to create a model that is partly based on observations, and matches what occurred historically. Future changes in sea level can therefore be predicted.

Results from the study showed that sea level was relatively stable from 200 B.C. to 1,000 A.D.

Sea level rose by almost half a millimeter a year for 400 years starting in the 11th century, known as the Medieval Climate Anomaly, when the climate started to warm, say researchers.

Then a second period of stable sea level associated with a cooler period known as the Little Ice Age occurred and lasted until the late 19th Century.

The study says that since the 19th Century, sea level has risen by more than 2 millimeters per year on average, which is considered the steepest rate for more than 2,100 years.

Researchers will present the findings to the United Nations on Tuesday, reports the AP.

Global warming and other man-made problems are to blame for the problems. These include dead zones from farm run-off, overfishing, increase in acidity from too much carbon dioxide, habitat destruction and melting sea ice.

The AP reports that a world-wide die-off of species that would rival past mass extinction will occur from the damaging effects on the seas.


Image 2: Expanse of salt marsh near Tump Point, N.C.; how long will its grasses remain above water? Credit: Andrew Kemp, Yale University

Image 3: Scanning electron microscope image of a common species of salt-marsh foraminifera. Credit: Andrew Kemp, Yale University


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