Greenland and Antarctica Already Melting at 'Worst-Case-Scenario' Rates
Antarctica and Greenland's ice sheets are currently melting at a pace consistent with worst-case-scenario predictions for sea level rise, with serious consequences for coastal communities and the reliability of climate models.
A paper published in Nature Climate Change Monday compared the latest satellite observations of polar ice melt with the predictions outlined in the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report. It found that the ice sheets are currently raising sea levels at a rate 45 percent above the IPCC's central prediction and closer to its worst-case scenario. If this continues, the two ice sheets could raise sea levels a further 17 centimeters (approximately 7 inches) more than central predictions by 2100.
"If ice sheet losses continue to track our worst-case climate warming scenarios we should expect an additional 17cm of sea level rise from the ice sheets alone," study coauthor and University of Leeds researcher Anna Hogg said in a university press release. "That's enough to double the frequency of storm-surge flooding in many of the world's largest coastal cities."
Ice sheets losses are tracking the IPCCs worst case climate predictions. This could mean an extra 17 cm of sea leve… https://t.co/wPdqTWef1D— CPOM News (@CPOM News)1598905099.0
Since the 1990s, the two ice sheets have already increased global sea levels by 1.8 centimeters (approximately 0.7 inches). But it was between 2007 and 2017 that the ice sheets began to lose mass at a rate consistent with worst-case-scenario projections, adding around 1.23 centimeters (approximately 0.5 inches) to the water line during that decade, according to the study.
A worst-case-scenario sea level rise as currently predicted would expose 44 to 66 million people to yearly coastal flooding by century's end. But one of study's most alarming implications is that, if sea level rise is already tracking worst-case-scenario predictions, the actual worst-case scenario could be even more dire.
"We need to come up with a new worst-case scenario for the ice sheets because they are already melting at a rate in line with our current one," lead author and Centre for Polar Observation and Modelling (CPOM) at the University of Leeds researcher Thomas Slater told AFP. "Sea level projections are critical in helping governments plan climate policy, mitigation and adaptation strategies. If we underestimate future sea level rise, then these measures may be inadequate and leave coastal communities vulnerable."
One of the reasons climate models might underestimate the worst-case scenario, Slater told AFP, is that they do not account for short-term weather changes such as the heat wave that drove Greenland's record melt in the summer of 2019.
The models that will be used for the IPCC's next report are better at predicting how the ice sheets, oceans and atmosphere interact, Slater said.
The latest study follows a slew of bad news for the world's ice. One study published in August found that the Greenland ice sheet had passed the "point of no return" and would continue to melt even if the climate crisis were halted.
Another recent study, also driven by Leeds' CPOM, calculated that the earth had lost 28 trillion tonnes (approximately 31 trillion U.S. tons) of ice in just 23 years.
These studies reflect a new global reality: In the last five years, melt from ice sheets and glaciers has outpaced the expansion of warming ocean water as the main cause of sea level rise.
"It is not only Antarctica and Greenland that are causing the water to rise," Dr. Ruth Mottram, a coauthor on Monday's study and a climate researcher at the Danish Meteorological Institute, told the University of Leeds. "In recent years, thousands of smaller glaciers have begun to melt or disappear altogether, as we saw with the glacier Ok in Iceland, which was declared 'dead' in 2014. This means that melting of ice has now taken over as the main contributor of sea level rise."
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By Aaron W Hunter
A chance discovery of a beautifully preserved fossil in the desert landscape of Morocco has solved one of the great mysteries of biology and paleontology: how starfish evolved their arms.
The Pompeii of palaeontology. Aaron Hunter, Author provided<h2></h2><p>Although starfish might appear very robust animals, they are typically made up of lots of hard parts attached by ligaments and soft tissue which, upon death, quickly degrade. This means we rely on places like the Fezouata formations to provide snapshots of their evolution.</p><p>The starfish fossil record is patchy, especially at the critical time when many of these animal groups first appeared. Sorting out how each of the various types of ancient starfish relate to each other is like putting a puzzle together when many of the parts are missing.</p><h2>The Oldest Starfish</h2><p><em><a href="https://www.biorxiv.org/content/10.1101/216101v1.full.pdf" target="_blank" rel="noopener noreferrer">Cantabrigiaster</a></em> is the most primitive starfish-like animal to be discovered in the fossil record. It was discovered in 2003, but it has taken over 17 years to work out its true significance.</p><p>What makes <em>Cantabrigiaster</em> unique is that it lacks almost all the characteristics we find in brittle stars and starfish.</p><p>Starfish and brittle stars belong to the family Asterozoa. Their ancestors, the Somasteroids were especially fragile - before <em>Cantabrigiaster</em> we only had a handful of specimens. The celebrated Moroccan paleontologist Mohamed <a href="https://doi.org/10.1016/j.palaeo.2016.06.041" target="_blank" rel="noopener noreferrer">Ben Moula</a> and his local team was instrumental in discovering <a href="https://www.sciencedirect.com/science/article/abs/pii/S0031018216302334?via%3Dihub" target="_blank" rel="noopener noreferrer">these amazing fossils</a> near the town of Zagora, in Morocco.</p><h2>The Breakthrough</h2><p>Our breakthrough moment came when I compared the arms of <em>Cantabrigiaster</em> with those of modern sea lilles, filter feeders with long feathery arms that tend to be attached to the sea floor by a stem or stalk.</p><p>The striking similarity between these modern filter feeders and the ancient starfish led our team from the University of Cambridge and Harvard University to create a new analysis. We applied a biological model to the features of all the current early Asterozoa fossils in existence, along with a sample of their closest relatives.</p>
Cantabrigiaster is the most primitive starfish-like animal to be discovered in the fossil record. Aaron Hunter, Author provided<p>Our results demonstrate <em>Cantabrigiaster</em> is the most primitive of all the Asterozoa, and most likely evolved from ancient animals called crinoids that lived 250 million years before dinosaurs. The five arms of starfish are a relic left over from these ancestors. In the case of <em>Cantabrigiaster</em>, and its starfish descendants, it evolved by flipping upside-down so its arms are face down on the sediment to feed.</p><p>Although we sampled a relatively small numbers of those ancestors, one of the unexpected outcomes was it provided an idea of how they could be related to each other. Paleontologists studying echinoderms are often lost in detail as all the different groups are so radically different from each other, so it is hard to tell which evolved first.</p>
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Listen:<iframe style="border: none" src="//html5-player.libsyn.com/embed/episode/id/17278520/height/45/theme/standard/thumbnail/yes/direction/backward/" height="45" width="100%" scrolling="no" allowfullscreen webkitallowfullscreen mozallowfullscreen oallowfullscreen msallowfullscreen></iframe><p><em>Reposted with permission from </em><em><a href="https://yaleclimateconnections.org/2021/01/college-course-teaches-students-how-to-be-climate-leaders/" target="_blank" rel="noopener noreferrer">Yale Climate Connections</a>.</em></p>
By Daniel Raichel
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