Polar Ice Caps Melting Six Times Faster Than in the 1990s
The polar ice caps are melting six times faster than they were in the 1990s, the most comprehensive look at the data to date has found.
That data, compiled and analyzed by the Ice Sheet Mass Balance Intercomparison Exercise (IMBIE), puts the melting of Greenland and Antarctica's ice sheets on track with the worst-case-scenario prediction from the Intergovernmental Panel on Climate Change (IPCC). If this trend continues, it could put 400 million people at risk from sea level rise by 2100.
"That's not a good news story," professor Andrew Shepherd from the University of Leeds told BBC News.
Shepherd helped lead an international team of 89 polar scientists who analyzed ice loss at both poles using 26 surveys and 11 satellite missions between 1992 and 2018, according to a University of Leeds press release.
They found that Greenland and Antarctica together lost 6.4 trillion tonnes (approximately 7.1 trillion U.S. tons) of ice between 1992 and 2017, raising global sea levels by 17.8 millimeters (approximately .7 inches). Not only that, but the rate of loss accelerated. The ice sheets lost 81 billion tonnes (approximately 89 billion U.S. tons) a year in the 1990s and 475 billion tonnes (approximately 524 billion U.S. tons) a year in the 2010s. This means they are now contributing much more to sea level rise.
"Today, the ice sheets contribute about a third of all sea-level rise, whereas in the 1990s, their contribution was actually pretty small at about 5%. This has important implications for the future, for coastal flooding and erosion," Shepherd told BBC News.
The Antarctica figures were published in Nature in 2018, while the Greenland figures were published in Nature this week.
The two polar regions have responded slightly differently, according to the press release. Ice melt in Antarctica has contributed 40 percent of the combined total sea level rise and is driven by warm ocean water melting its glaciers. Ice melt in Greenland, which accounts for 60 percent of the sea level rise, is driven partly by ocean water but partly by warmer air temperatures melting the surface of its ice sheet.
"The satellite measurements provide prima facie, rather irrefutable, evidence," he said.
The findings have serious consequences for the future. The IPCC most recently predicted sea levels would rise 53 centimeters (approximately 21 inches) by 2100, putting 360 million people at risk from coastal flooding every year. But, the new data puts sea levels on track to rise an additional 17 centimeters (approximately 6.7 inches). This would increase the number of people at risk from yearly coastal flooding by 2100 to 400 million.
"These are not unlikely events with small impacts; they are already underway and will be devastating for coastal communities," Shepherd said in the press release.
However, this future is not inevitable. While Shepherd told The Guardian that the ice caps would melt for another 30 years even if greenhouse gas emissions ceased today, there is still time to limit the amount of melting.
"We can offset some of that [sea level rise] if we stop heating the planet," he said.
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The ghoulishly named ogre-faced spider can "hear" with its legs and use that ability to catch insects flying behind it, the study published in Current Biology Thursday concluded.
"Spiders are sensitive to airborne sound," Cornell professor emeritus Dr. Charles Walcott, who was not involved with the study, told the Cornell Chronicle. "That's the big message really."
The net-casting, ogre-faced spider (Deinopis spinosa) has a unique hunting strategy, as study coauthor Cornell University postdoctoral researcher Jay Stafstrom explained in a video.
They hunt only at night using a special kind of web: an A-shaped frame made from non-sticky silk that supports a fuzzy rectangle that they hold with their front forelegs and use to trap prey.
They do this in two ways. In a maneuver called a "forward strike," they pounce down on prey moving beneath them on the ground. This is enabled by their large eyes — the biggest of any spider. These eyes give them 2,000 times the night vision that we have, Science explained.
But the spiders can also perform a move called the "backward strike," Stafstrom explained, in which they reach their legs behind them and catch insects flying through the air.
"So here comes a flying bug and somehow the spider gets information on the sound direction and its distance. The spiders time the 200-millisecond leap if the fly is within its capture zone – much like an over-the-shoulder catch. The spider gets its prey. They're accurate," coauthor Ronald Hoy, the D & D Joslovitz Merksamer Professor in the Department of Neurobiology and Behavior in the College of Arts and Sciences, told the Cornell Chronicle.
What the researchers wanted to understand was how the spiders could tell what was moving behind them when they have no ears.
It isn't a question of peripheral vision. In a 2016 study, the same team blindfolded the spiders and sent them out to hunt, Science explained. This prevented the spiders from making their forward strikes, but they were still able to catch prey using the backwards strike. The researchers thought the spiders were "hearing" their prey with the sensors on the tips of their legs. All spiders have these sensors, but scientists had previously thought they were only able to detect vibrations through surfaces, not sounds in the air.
To test how well the ogre-faced spiders could actually hear, the researchers conducted a two-part experiment.
First, they inserted electrodes into removed spider legs and into the brains of intact spiders. They put the spiders and the legs into a vibration-proof booth and played sounds from two meters (approximately 6.5 feet) away. The spiders and the legs responded to sounds from 100 hertz to 10,000 hertz.
Next, they played the five sounds that had triggered the biggest response to 25 spiders in the wild and 51 spiders in the lab. More than half the spiders did the "backward strike" move when they heard sounds that have a lower frequency similar to insect wing beats. When the higher frequency sounds were played, the spiders did not move. This suggests the higher frequencies may mimic the sounds of predators like birds.
University of Cincinnati spider behavioral ecologist George Uetz told Science that the results were a "surprise" that indicated science has much to learn about spiders as a whole. Because all spiders have these receptors on their legs, it is possible that all spiders can hear. This theory was first put forward by Walcott 60 years ago, but was dismissed at the time, according to the Cornell Chronicle. But studies of other spiders have turned up further evidence since. A 2016 study found that a kind of jumping spider can pick up sonic vibrations in the air.
"We don't know diddly about spiders," Uetz told Science. "They are much more complex than people ever thought they were."
Learning more provides scientists with an opportunity to study their sensory abilities in order to improve technology like bio-sensors, directional microphones and visual processing algorithms, Stafstrom told CNN.
"The point is any understudied, underappreciated group has fascinating lives, even a yucky spider, and we can learn something from it," he told CNN.
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