Antarctic Glacial Melt May Be Irreversible Causing Sea Rise, Research Says
A glacier the size of Florida is melting much faster than expected and may soon trigger a 50cm, or 19.6 inches, rise in sea level, according to a new NASA-funded study published online by the Proceedings of the National Academy of Sciences.
The study found that in the last six years, several closely observed Antarctic glaciers have doubled their rate of melting. Their rate of melting was five times faster than in the 1990s. The Thwaites Glacier, one of five recently studied unstable glaciers, which measures about 70,000 square miles is at risk of rapidly melting into the ocean, triggering an unstoppable rise in sea levels.
The mathematical models the researchers created make the most catastrophic scenarios of rapid melting and fast rises in sea water levels seems much more likely than the best-case scenarios of a slow sea level rise. Just how much ice the glaciers will shed in the next 50 to 800 years is impossible to predict since the climate is constantly changing and more data is needed. And yet, the researchers at the Georgia Institute of Technology, NASA Jet Propulsion Laboratory, and the University of Washington factored the instability into 500 ice flow simulations for Thwaites with refined calculations, according to Phys.org.
While the scenarios showed a wide-range of possibilities, they consistently pointed to an irreversible instability in the glacier that would keep pushing the ice out to sea at an enormously accelerated rate over the coming centuries.
A complete loss of the West Antarctic ice sheet would be expected to increase global sea levels by about five meters (16ft), which would submerge coastal cities around the world. In some models, the entire ice sheet could be lost within 150 years, even if global temperatures stopped rising, which they show no sign of doing, according to the Guardian.
"If you trigger this instability, you don't need to continue to force the ice sheet by cranking up temperatures. It will keep going by itself, and that's the worry," said Alex Robel, an assistant professor at Georgia Tech and the study's lead author, as the Independent reported. "Climate variations will still be important after that tipping point because they will determine how fast the ice will move."
This study comes on the heels of another study published in the same journal that looked at satellite images of the continent and found a swath of ice four times larger than France has melted since 2014, as EcoWatch reported.
Antarctica is an overwhelming ice juggernaut. It has nearly eight times as much land-based ice than the Greenland ice sheet and 50 times more than all the mountain glaciers in the world combined. The Thwaites glacier alone contains enough ice to increase global sea levels by about 50cm, or more than 19.6 inches, which is alarming since sea level rise due to global warming is already linked to increased coastal flooding and storm surges, according to the Guardian.
Current sea levels are already 8-inches above pre-industrial levels and the annual rate of sea level rise has doubled since 1990.
"You want to engineer critical infrastructure to be resistant against the upper bound of potential sea level scenarios a hundred years from now," said Robel, as the Independent reported. "It can mean building your water treatment plants and nuclear reactors for the absolute worst-case scenario, which could be two or three feet of sea level rise from Thwaites Glacier alone, so it's a huge difference."
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By Katherine Kornei
Clear-cutting a forest is relatively easy—just pick a tree and start chopping. But there are benefits to more sophisticated forest management. One technique—which involves repeatedly harvesting smaller trees every 30 or so years but leaving an upper story of larger trees for longer periods (60, 90, or 120 years)—ensures a steady supply of both firewood and construction timber.
A Pattern in the Rings<p>The <a href="https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/coppice-standards-0" target="_blank">coppice-with-standards</a> management practice produces a two-story forest, said <a href="https://www.researchgate.net/profile/Bernhard_Muigg" target="_blank">Bernhard Muigg</a>, a dendrochronologist at the University of Freiburg in Germany. "You have an upper story of single trees that are allowed to grow for several understory generations."</p><p>That arrangement imprints a characteristic tree ring pattern in a forest's upper story trees (the "standards"): thick rings indicative of heavy growth, which show up at regular intervals as the surrounding smaller trees are cut down. "The trees are growing faster," said Muigg. "You can really see it with your naked eye."</p><p>Muigg and his collaborators characterized that <a href="https://ltrr.arizona.edu/about/treerings" target="_blank">dendrochronological pattern</a> in 161 oak trees growing in central Germany, one of the few remaining sites in Europe with actively managed coppice-with-standards forests. They found up to nine cycles of heavy growth in the trees, the oldest of which was planted in 1761. The researchers then turned to a historical data set — more than 2,000 oak <a href="https://eos.org/articles/podcast-discovering-europes-history-through-its-timbers" target="_blank" rel="noopener noreferrer">timbers from buildings and archaeological sites</a> in Germany and France dating from between 300 and 2015 — to look for a similar pattern.</p>
A Gap of 500 Years<p>The team found wood with the characteristic coppice-with-standards tree ring pattern dating to as early as the 6th century. That was a surprise, Muigg and his colleagues concluded, because the first mention of this forest management practice in historical documents occurred only roughly 500 years later, in the 13th century.</p><p>It's probable that forest management practices were not well documented prior to the High Middle Ages (1000–1250), the researchers suggested. "Forests are mainly mentioned in the context of royal hunting interests or donations," said Muigg. Dendrochronological studies are particularly important because they can reveal information not captured by a sparse historical record, he added.</p><p>These results were <a href="https://www.nature.com/articles/s41598-020-78933-8" target="_blank">published in December in <em>Scientific Reports</em></a>.</p><p>"It's nice to see the longevity and the history of coppice-with-standards," said <a href="https://www.teagasc.ie/contact/staff-directory/s/ian-short/" target="_blank">Ian Short</a>, a forestry researcher at Teagasc, the Agriculture and Food Development Authority in Ireland, not involved in the research. This technique is valuable because it promotes conservation and habitat biodiversity, Short said. "In the next 10 or 20 years, I think we'll see more coppice-with-standards coming back into production."</p><p>In the future, Muigg and his collaborators hope to analyze a larger sample of historic timbers to trace how the coppice-with-standards practice spread throughout Europe. It will be interesting to understand where this technique originated and how it propagated, said Muigg, and there are plenty of old pieces of wood waiting to be analyzed. "There [are] tons of dendrochronological data."</p><p><em><a href="mailto:email@example.com" target="_blank" rel="noopener noreferrer">Katherine Kornei</a> is a freelance science journalist covering Earth and space science. Her bylines frequently appear in Eos, Science, and The New York Times. Katherine holds a Ph.D. in astronomy from the University of California, Los Angeles.</em></p><p><em>This story originally appeared in <a href="https://eos.org/articles/tree-rings-reveal-how-ancient-forests-were-managed" target="_blank">Eos</a></em> <em>and is republished here as part of Covering Climate Now, a global journalism collaboration strengthening coverage of the climate story.</em></p>
Earth's ice is melting 57 percent faster than in the 1990s and the world has lost more than 28 trillion tons of ice since 1994, research published Monday in The Cryosphere shows.
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