Climate scientists have long predicted that global warming will melt polar ice sheets and cause sea levels to rise throughout the century, potentially swamping island nations and flooding low-lying coastal cities. But exactly how much ocean waters will rise has yet to be settled. Now, two studies have come out that at first appear to contradict each other, leading to clashing headlines like “An Inconvenient Truth” Exaggerated Sea Level Rise [Telegraph], and Sea Level Rise May Be Twice More Than Expected [Discovery News].
One study seems to downplay the risk of an extreme sea-level rise, while the other hypes it up. But a closer look reveals that the two studies actually bring researchers nearer to scientific consensus.
In the study published in Science [subscription required], researchers examined the hypothesis of a six-foot sea-level rise by 2100, and calculated how quickly the ice sheets in Greenland and Antarctica would have to melt into the oceans to produce this effect. Their calculations showed that the glaciers would have to essentially gallop towards the sea, which seems an unlikely outcome. In Greenland, the glaciers moving into the island’s calving fjords would have to increase their speed to 28.4 miles per year and sustain that speed until the end of the century [Telegraph]. These researchers believe the most plausible scenario is a sea-level rise of between two and six feet within this century. As their results have been compared to more radical estimates like the 20-foot rise mentioned in the documentary film An Inconvenient Truth, the findings are being greeted with relief.
Meanwhile, a paper published in Nature Geoscience [subscription required] ultimately came to a similar estimate, but was presented very differently. Researchers looked at what had happened at the end of the last ice age, when the last fragments of the Laurentide ice sheet covered much of north-eastern Canada [New Scientist]. They studied the geological record and used computer simulations to determine how long it took the Laurentide ice sheet to melt away completely and how much it raised sea levels, and determined that the event raised ocean levels about three feet per century.
These researchers say that atmospheric conditions at the end of the last ice age are similar to what the world will experience before 2100, and say the vast Greenland ice sheet could begin to melt more rapidly than expected towards the end of the century, accelerating the rise in sea levels [Guardian]. But while the three-foot rise this model predicts is in line with the other study’s estimate, it has gotten a different reception. Because it was compared to the UN’s Intergovernmental Panel on Climate Change official estimate of a seven-inch to two-foot rise by 2100, this second study has been presented as an alarm bell.
The take-home point is that both research groups say the world is likely to see oceans rise by at least two feet before the end of the century, which would still cause trouble for coastal nations like Bangladesh and the Netherlands, and could bring more damaging floods to U.S. cities like New York and New Orleans. Says Tad Pfeffer, one study’s author: Just because the amount of sea-level rise predicted in the new study is “not a Hollywood cataclysm, it doesn’t mean it’s not important” [National Geographic News].
Image: flickr/Stig Nygaard