Climate change: Earth’s deepest ice canyon vulnerable to melting

Climate change: Earth’s deepest ice canyon vulnerable to melting

SOURCE: BBC DATE: March 23, 2020 SNIP: East Antarctic’s Denman Canyon is the deepest land gorge on Earth, reaching 3,500m below sea-level. It’s also filled top to bottom with ice, which US space agency (Nasa) scientists reveal in a new report has a significant vulnerability to melting. Retreating and thinning sections of the glacier suggest it is being eroded by encroaching warm ocean water. Denman is one to watch for the future. If its ice were hollowed out, it would raise the global sea surface by 1.5m. Most people recognise the shores around the Dead Sea in the Middle East to have the lowest visible land surface elevation on Earth, at some 430m below sea level. But the base of the gorge occupied by Denman Glacier on the edge of the East Antarctic Ice Sheet (EAIS) actually reaches eight times as deep. Dr Brancato and colleagues used satellite radar data from 1996 to 2018 to show there’s been a marked retreat in the glacier’s grounding line. This is the point where the ice stream lifts up and floats as it flows off the land and enters the ocean. The line has reversed 5-6km in 22 years. What’s interesting about this reversal, however, is that it’s asymmetric; it’s occurring pretty much all on the western side of the glacier. The reason, the scientists can now determine, is a buried ridge under the eastern flank which is pinning and protecting that side of the glacier. In contrast, the western flank features a narrow but sizeable trough that would allow warm ocean water to erode the grounding line and push it backwards....
Polar ice caps melting six times faster than in 1990s

Polar ice caps melting six times faster than in 1990s

SOURCE: The Guardian DATE: March 11, 2020 SNIP: The polar ice caps are melting six times faster than in the 1990s, according to the most complete analysis to date. The ice loss from Greenland and Antarctica is tracking the worst-case climate warming scenario set out by the Intergovernmental Panel on Climate Change (IPCC), scientists say. Without rapid cuts to carbon emissions the analysis indicates there could be a rise in sea levels that would leave 400 million people exposed to coastal flooding each year by the end of the century. Rising sea levels are the one of the most damaging long-term impacts of the climate crisis, and the contribution of Greenland and Antarctica is accelerating. The new analysis updates and combines recent studies of the ice masses and predicts that 2019 will prove to have been a record-breaking year when the most recent data is processed. The previous peak year for Greenland and Antarctic ice melting was 2010, after a natural climate cycle led to a run of very hot summers. But the Arctic heatwave of 2019 means it is nearly certain that more ice was lost last year. The average annual loss of ice from Greenland and Antarctica in the 2010s was 475bn tonnes – six times greater than the 81bn tonnes a year lost in the 1990s. In total the two ice caps lost 6.4tn tonnes of ice from 1992 to 2017, with melting in Greenland responsible for 60% of that figure. The IPCC’s most recent mid-range prediction for global sea level rise in 2100 is 53cm. But the new analysis suggests that if current trends continue...
Scientists Find Record Warm Water in Antarctica, Pointing to Cause Behind Troubling Glacier Melt

Scientists Find Record Warm Water in Antarctica, Pointing to Cause Behind Troubling Glacier Melt

SOURCE: NYU DATE: January 29,2020 SNIP: A team of scientists has observed, for the first time, the presence of warm water at a vital point underneath a glacier in Antarctica—an alarming discovery that points to the cause behind the gradual melting of this ice shelf while also raising concerns about sea-level rise around the globe. The recorded warm waters—more than two degrees above freezing—flow beneath the Thwaites Glacier, which is part of the Western Antarctic Ice Sheet. The discovery was made at the glacier’s grounding zone—the place at which the ice transitions between resting fully on bedrock and floating on the ocean as an ice shelf and which is key to the overall rate of retreat of a glacier. Thwaites’ demise alone could have significant impact globally. It would drain a mass of water that is roughly the size of Great Britain or the state of Florida and currently accounts for approximately 4 percent of global sea-level rise. Some scientists see Thwaites as the most vulnerable and most significant glacier in the world in terms of future global sea-level rise—its collapse would raise global sea levels by nearly one meter, perhaps overwhelming existing populated areas. While the glacier’s recession has been observed over the past decade, the causes behind this change had previously not been determined. The scientists’ measurements were made in early January, after the research team created a 600-meter deep and 35-centimeter wide access hole and deployed an ocean-sensing device to measure the waters moving below the glacier’s surface. This device gauges the turbulence of the water as well as other properties such as temperature. The result...
Scientists find far higher than expected rate of underwater glacial melting

Scientists find far higher than expected rate of underwater glacial melting

SOURCE: Phys.org DATE: January 29, 2020 SNIP: Tidewater glaciers, the massive rivers of ice that end in the ocean, may be melting underwater much faster than previously thought, according to a Rutgers co-authored study that used robotic kayaks. The findings, which challenge current frameworks for analyzing ocean-glacier interactions, have implications for the rest of the world’s tidewater glaciers, whose rapid retreat is contributing to sea-level rise. The study, published in the journal Geophysical Research Letters, surveyed the ocean in front of 20-mile-long LeConte Glacier in Alaska. The seaborne robots made it possible for the first time to analyze plumes of meltwater, the water released when snow or ice melts, where glaciers meet the ocean. It is a dangerous area for ships because of ice calving—when falling slabs of ice that break from glaciers crash into the water and spawn huge waves. “With the kayaks, we found a surprising signal of melting: Layers of concentrated meltwater intruding into the ocean that reveal the critical importance of a process typically neglected when modeling or estimating melt rates,” said lead author Rebecca Jackson, a physical oceanographer and assistant professor in the Department of Marine and Coastal Sciences in the School of Environmental and Biological Sciences at Rutgers University-New Brunswick. Two kinds of underwater melting occur near glaciers. Where freshwater discharge drains at the base of a glacier (from upstream melt on the glacier’s surface), vigorous plumes result in discharge-driven melting. Away from these discharge outlets, the glacier melts directly into the ocean waters in a regime called ambient melting. The study follows one published last year in the journal Science that measured...
New Zealand glaciers turn brown from Australian bushfires’ smoke, ash and dust

New Zealand glaciers turn brown from Australian bushfires’ smoke, ash and dust

SOURCE: The Guardian DATE: January 1, 2020 SNIP: Snow and glaciers in New Zealand have turned brown after being exposed to dust from the Australian bushfires, with one expert saying the incident could increase glacier melt this season by as much as 30%. On Wednesday many parts of the South Island woke up to an orange haze and red sun, after smoke from the Victorian and New South Wales blazes drifted east on Tuesday night, smothering many parts of the island for most of the day. On Thursday, pictures taken from the Southern Alps showed the smoke haze carrying particles of dust had tinged snow-capped mountain peaks and glaciers a shade of caramel, with former prime minister Helen Clark expressing concern for the long-lasting environmental impacts on the mountains. “Impact of ash on glaciers is likely to accelerate melting,” Clark tweeted. “How one country’s tragedy has spillover effects.” There are more than 3,000 glaciers in New Zealand and since the 1970s scientists have recorded them shrinking by nearly a third, with current estimates predicting they will disappear entirely by the end of the century. Professor Andrew Mackintosh is head of the school of earth, atmosphere and environment at Monash University, and the former director of the Antarctic Research Centre. He said in nearly two decades of studying glaciers in New Zealand he had never seen such a quantity of dust transported across the Tasman, and the current event had the potential to increase this season’s glacier melt by 20-30%, although Mackintosh stressed this was no more than an estimate. Mackintosh said the whiteness of snow and ice reflected the...