Al Gore’s movie ‘An Inconvenient Truth’ says sea levels could rise up to 20 feet. Is this true?
Asks Steve from Florida
Some of the most memorable images from Al Gore’s movie, An Inconvenient Truth, are the graphics that show how rising ocean levels will dramatically alter our planet’s coastlines. As
Although he doesn’t give a clear time frame for the 20-foot sea level rise, Gore’s statement seems to contradict several recent reports, including one published in 2008, that predict much smaller rises during this century.
Scientists say that the two main causes of rising sea levels are water expanding as it warms, known as thermal expansion, and melting land-based ice, such as ice from
In 2007, the International Panel on Climate Change, an organization composed of scientists and policy makers around the world who monitor human-caused climate change, estimated that sea levels would rise 0.18 to 0.6 meters (0.59 to 2.0 feet) over the next 100 years. The IPCC based this prediction primarily on how much the ocean waters are expected to warm and expand.
The panel also factored in the ice melting from
The IPCC did not include changes in ice flow because these types of changes are not very well understood. However, a study published this year in the journal Science attempts to set an upper limit on sea level rise by 2100.
“We have estimated limits on sea level rise during the next century by considering simple constraints on glacier and ice sheet motion,” says Joel Harper, an author of this study and a glacier expert at the
To make their calculations, the researchers took into account the rate of ice flow from
The researchers also determined that
“Even by assuming vastly accelerated rates of discharge, the glaciers can’t surge fast enough to meet the required sea-level rise targets [of two to five meters] within a hundred years,” says Vivien Gornitz, a geologist at Columbia University, who was not involved in this study.
While this new sea-level rise estimate is much lower than Gore’s 20-foot prediction, it is still significant.
“An enormous number of people live within one meter of sea level. It is something like 145 million people,” says glacier expert Harper
The researchers think that knowing how high sea levels may rise will let countries gauge how much they need to spend on new infrastructure, such as levees, to prepare for changes to their coastlines.
Harper hopes that further research will lead to more precise estimates. “Learning more about the physics which govern glacier dynamics will be a big step,” he says.
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