Al Gore’s movie ‘An Inconvenient Truth’ says sea levels could rise up to 20 feet. Is this true?

Asks Steve from Florida

The Maldives, a group of Indian Ocean islands, could be threatened by even a meter rise in sea level.
[Credit: Nattu, flickr.com]

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 Greenland’s ice sheets collapse, Gore predicts that our shores will be flooded and sea-bordering cities will sink beneath the water leaving millions of people homeless. His narration tells the audience that, due to global warming, melting ice could release enough water to cause at 20-foot rise in sea level “in the near future.”

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 Antarctica and Greenland.

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 Greenland and Antarctica based on how much these bodies have melted in recent years—from 1993 to 2003. But the estimates do not account for any changes in the speed of the weakened ice that flows from the glaciers into the ocean—either from melting ice or iceberg break-off, which may happen in the future. The IPCC acknowledged the limitations of their projections and said that sea level rise could be higher if the ice sheets break down more rapidly.

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 University of Montana in Missoula. “Our work suggests that a 0.8-meter [2.6 feet] sea level rise is plausible, two-meter [6.5 feet] is only possible under extreme conditions, and more than two-meter is unlikely,” he says.

To make their calculations, the researchers took into account the rate of ice flow from Greenland, Antarctica, and glaciers and ice caps from other parts of the world. They took current values of glacial ice-flow speeds and adjusted the values based on changes that they think could reasonably occur in the future, such as accelerated ice flow from certain glaciers. They then used these modified values to come up with low, medium and high estimates of future sea-level rise.

The researchers also determined that Greenland’s glaciers—specifically, the ones with outlets under water—would have to move about 40 times faster than they do now to achieve a rise of two meters over the next 100 years. And this increased ice-flow speed would need to start immediately and continue for the rest of the 21st century.

“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. “Most of these are in third world Asia where they have few resources to adapt to change. Even in the US, the costs will be enormous,” he adds.

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.

Related on Scienceline:

One meter or two?—Ask an ice shelf

Will dumping iron into the ocean slow down global warming?

Oceans in trouble: garbage, overfishing and acidification (oh my!)

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  1. Some other research to ponder:

    Response of the global ocean to Greenland and Antarctic ice melting -
    D. Stammer, Institut für Meereskunde, Universität Hamburg, Hamburg, Germany

    Millennial Atmospheric Lifetime of Fossil Fuel CO2, D. Archer and V. Brovkin, Climatic Change 90:283-297, 2008.

    D.Stammers study looks at the flow of water around the world and points out that it takes a number of decades for water deposited in the Atlantic to distribute around the worlds oceans. eg. the Atlantic may ‘bulge’ initially so that sea levels are higher at Atlantic coasts.

    I’m not sure how much this applies to current rates of break up, melting.

    But even if it takes one thousand years to reach 20 ft, does the time scale matter?
    As D. Archer (Chicago Uni) points out, a proportion of CO2 we emit today will remain in the atmosphere for thousands of years (if we don’t do anything to draw it down). So maybe Gore got the time scales wrong (or not so wrong?) but if we carry on as we are, massive sea level rises are inevitable.

    Paul, December 1, 2008 at 5:22 am
  2. To the young people out there, every so many years we must face another claimed historic calamity for our planet. Al Gore is adding his alrmist hysteria. His outlandish projections are not supported by the scientific community. If he didn’t have the nerve to claim a 20ft water level increase no one would listen. In recent history claims of a 1 degree rise and drop in earth temp have caused mini hysteria.I guess that means that we are at the optimum temp today. What drivel!

    terry, April 17, 2009 at 12:47 pm
  3. I don’t really care if Al Gore was off on his calculations. What he’s trying to do is try to make people feel the need to help the earth. If fear is the only way to get people to start helping, I say go for it! People don’t seem to notice the severity of things until something big happens, and, by then, it’s usually too late.

    Alexis, May 14, 2009 at 4:08 pm
  4. So, I have been studying the reported temperatures in Connecticut, USA for the past year and guess what? Average temp is down! OK, one years’ worth of data isn’t enough….but what is? The projections used in “An Inconvenient truth” come from models, which have not been tested. In fact, the models cannot predict weather or temperatures in any particular geographic region, they only predict averages for the entire world. The predictions are wrong. They’re better than they were, but they are still off by a great extent.
    My answer: keep observing the world around us; report the facts as observed; take action when necessary; keep your money in your pcket until it is time to do something.

    Jeff, June 22, 2009 at 1:11 pm
  5. “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.” The construction of levies would simply add more CO2 to the environment as would the building of new housing. The people who are below sea level will have to move but to where?
    Too much time is spent on nitpicking the scientific results. The heat is rising, the poles & glaciers are melting, and if anything the conservative scientific community has under estimated both the rapidity of the enormity of the changes. Our species does not have the smarts to deal with this problem.

    Stuey, November 7, 2009 at 5:20 pm
  6. Al Gore is a liar. His Church of Climatology brooks no oppossition.Al gore is not about “helping the earth” but about lining his own pockets with his phoney envoirnmentalism. Lord Momckton a British Climatologist and A British hight court Judge have both refuted his lies. His propagandistic film an “Inconvenient Truth, Should be renamed “An Opportunistic Lie” The Un Climate panel has falisfied data and told outright lies to prove the political point of that there is man made global warming. Former Un climate panel scientists have resigned from the oanel in protest at this and the fact that their reports are being edited by civil servants. Manmade made global warming is a scam, a political underpinned by junk science.

    Tony, November 23, 2009 at 9:47 am
  7. @ Stuey: “The people who are below sea level will have to move but to where?”
    Well Stuey, thanks to global warming, land that was once covered by glaciers will now be inhabitable!

    @ Alexis: If you are ok with the perpetuation of lies that is your prorogative but it is shameful to dupe the world so that you can get your way, isn’t that what Hitler did with what he viewed as a “problem.” Seriously, donate to Gore’s propaganda fund all you want but don’t justify the lies.

    I am an environmentalist, always have been, and it’s been a struggle to show, teach, and convince people to live environmentally friendly and live sustainably and hacks like Gore are destroying all the work that has been done by perpetuation the lies. Gore is an opportunistic liar and because of Hollywood’s new pet project (jumping on Gore’s band wagon) the simple masses are forgetting what really matter to the environment and calling for taxing of industry and shuttting down the oil sands; the very sources that supplies our wasteful over consumerism. The real work needs to be done at the individual level. Copenhagen and Gore are destroying the environmental cause and feeding the fanatics.

    Whatever stuey, December 15, 2009 at 11:50 pm
  8. Let’s not forget about the disappearance of the island of Atlantis and the Great Flood that Noah endured. We need to blame Global Warming for that too.

    Cole, March 26, 2010 at 10:48 am
  9. Gore is fulla of it. If he believed this nonsense, explain why he bought luxury digs at sea level in Montecito, Ca., and San Frisco? Sorry, but you have to Google it yourself. Our server is owned by Gorebots so we cannot link to articles.

    judgeroybean, September 4, 2011 at 9:42 pm
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