Antarctic Melting Could|Double Sea-Level Rise

     
     (CN) – Scientists have underestimated the impact of Antarctic ice-sheet melting on global sea levels, which one group of researchers now believe may rise 50 feet in the next 500 years if greenhouse gas emissions continue.
     The massive West Antarctic ice sheet – one of the final leftovers from the last ice age – is larger than Mexico, and capable of raising global sea level by 12 feet or more due to its significant width and depth. While scientists had presumed that it would take hundreds of years for the worst effects of the ice-sheet melting to manifest, new research indicates that they may occur much sooner.
     If greenhouse gas emissions continue unabated, the next generation will likely see a sea-level rise of about three to six feet by 2100, according to a recent study by researchers from Penn State and the University of Massachusetts, Amherst. The rising seas would leave cities like Hong Kong, New York, Miami, London and Venice at risk of being completely inundated.
     This researchers’ projection is about twice the increase that was predicted by the United Nation’s Intergovernmental Panel on Climate Change, which aggregated recent studies in order to determine the most likely outcomes based on efforts – or lack there of – to curb greenhouse gas emissions.
     While the U.N. group projected that sea levels will most likely rise about three feet by 2100, Dr. Peter Clark, a professor of geosciences at Oregon State University who led the U.N. project, acknowledged that additional variables could be measured for more nuanced estimates.
     The universities’ research measures the influence of atmospheric warming, which many other studies had failed to properly quantify.
     “We’ve added some physics to the model that are linked to the atmosphere, so now the ice sheet is being attacked from the bottom up and the top down in our model,” Dr. Robert DeConto, a professor geosciences at the University of Massachusetts, Amherst, said. “We ended up getting a much bigger response than these previous studies.”
     DeConto and Dr. David Pollard, a geoscientist at Penn State and co-author of the study, spent years working on ice-sheet modeling. The pair created a computerized climate model that accounted for Antarctica’s complex landscape of glaciers and rocks, which in turn highlighted the potential danger to the ice sheet’s stability.
     The combination of enhanced geographical detailing and accounting for atmospheric warming allowed the researchers to establish a climate model that predicted more severe outcomes than other projections.
     “They work in tandem. The first happens, and that allows the other to happen,” Pollard said.
     In order to confirm their projections for the future of Antarctica, the scientists reproduced climate scenarios from 125,000 years ago, when sea levels were about 20 to 30 feet higher than today.
     Once the model was able to account for the variables and physics that led to past sea-level rise, including other time periods, the researchers knew that their climate model was accurate.
     “This is another place where we’re doing something a little different from these other studies. We are using these past sea-level events to validate the model, to verify that it’s doing something reasonable,” DeConto said. “The models are being tuned and calibrated to actual past high-sea-level events.”
     While governments around the world still have time to curb greenhouse gas emissions and avoid some of the dire projections, the scientists’ climate models provide an overview of what will happen if current trends continue: The researchers found that sea levels would rise by about a foot per decade by the middle of the 22nd century.
     The West Antarctic ice sheet is protected by floating ice shelves, which serve as a buttress against warmer water that could melt and destabilize the sheet. Smaller ice shelves have already melted, perhaps most notably in 2002 with the Larsen B shelf, which was about the size of Rhode Island.
     Once ice shelves melt and West Antarctica becomes more unstable, it could begin to break apart midway through the 21st century.
     The East Antarctica ice sheet, with less direct exposure to warming sea temperatures, would take longer to melt. The scientists projected that it could melt by around 2500, leading to a sea-level rise of approximately 43 feet.
     The magnitude of sea-level rise led nations around the world to sign off on the Paris climate agreement this past December, which aims to keep global average temperature rise below two degrees Celsius.
     Global average temperatures increasing by more than two degrees Celsius would lead to more severe outcomes, including enhanced sea-level rise. The scientists’ model projects that global temperature increases will exceed that threshold.
     “If everybody follows through with the agreements that have been ratified so far, it keeps global temperature rise to a little less than three degrees (Celsius),” DeConto said.
     Based on their data, the Paris climate agreement is insufficient to prevent Antarctica from melting at a dangerous rate.
     “This is just one model, and David and I are just one small research team doing this work. But according to these results, it would imply that the way the Paris agreement stands right now, it’s actually not enough,” DeConto said. “And that’s if everyone comes through with what they’ve agreed to. We’d have to keep global temperature rise below two degrees (Celsius).”
     DeConto pointed out that while the consequences of maintaining the present level of greenhouse gas emissions are significant, there is still time to change the current trend.
     “We’re suggesting this really dramatic range of sea-level futures. The good news in all of this is if emissions are reduced beginning very soon, then there’s very little contribution from Antarctica, versus the business as usual scenario where there’s really dramatic potential sea-level rise,” DeConto said.
     The Paris climate agreement is expected to be signed later this month in New York, one of the cities that would be affected by rising sea levels.
     The study was supported by the National Science Foundation and published in the journal Science.
     
     Photo Credit: NASA/Jim Yungel

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