Greenland Lost 600 Billion Tons of Ice Last Summer, Raising Sea Levels, NASA Study Finds
Greenland experienced an unusually warm summer in 2019, which caused the world's largest island to lose 600 billion tons of ice and raised sea levels by 0.2 of an inch, according to a NASA study released yesterday. That amount of ice loss more than doubled Greenland's 2002-2019 annual average.
The data comes from the joint U.S.-German space mission known as Grace-FO, a pair of satellites that circle the globe and sense the variations in mass that correspond to Earth's gravity field, according to the BBC. The satellites are particularly adept at sensing tiny changes in the Earth's gravitational field caused by ice gain or loss. They have proven themselves useful in detecting groundwater storage around the globe, according to the Washington Post.
The study also looked at Antarctica, noting that it continues to lose its ice mass, particularly in the Amundsen Sea Embayment and the Antarctic Peninsula on the western part of the continent, according to NASA's Jet Propulsion Laboratory.
"We knew this past summer had been particularly warm in Greenland, melting every corner of the ice sheet," lead author Isabella Velicogna, senior project scientist at the Jet Propulsion Laboratory and a professor at University of California, Irvine, said in a statement. "But the numbers really are enormous."
The study was published in the journal Geophysical Research Letters. It tracked ice loss in Greenland dating back to 2002, using information from the Gravity Recovery and Climate Experiment (Grace) satellites, which went out of commission in 2017, and the new Grace-FO satellites, which launched in 2018. The FO stands for Follow On, as The Washington Post reported.
The satellites revealed that from 2002 to 2019, Greenland lost 4,550 billion tons of ice, for an average of 261 billion tons every year, according to The Washington Post. 2012 and 2019 were the two largest melt years in that time frame, the BBC reported.
Velicogna told The Washington Post what made 2019 so different in Greenland was that there was a lot of melting from the glaciers in the north and northeastern glaciers, which is unusual.
"And, so, basically, we have melting all around the ice sheet," she said.
In the coastal town of Ilulissat, not far from where the mighty Jakobshavn Glacier enters the ocean, temperatures reached into the high 20s Celsius this summer. The warm temperatures even reached the ice sheet's interior, which approached above freezing levels, the BBC reported.
"It's significant that we're now seeing melt and mass loss extending to Greenland's northern glaciers. All of Greenland contributed to the big summer melt of last year," Velicogna said, according to the BBC.
Robin Bell, an expert on ice sheet dynamics at Columbia University, to The Washington Post that the satellite data will help researchers improve the accuracy of their future sea-level rise estimates.
"This is a beautiful update of how we can really see how the ice sheets are changing…from the annual inhale and exhale as snow accumulates in the winter in Greenland and melts in the summer," she 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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