An international team of Antarctic scientists was surprised by their shocking discovery that the rate of Antarctic ice melting has tripled since 2012. www.nature.com/...
Here we combine satellite observations of its changing volume, flow and gravitational attraction with modelling of its surface mass balance to show that it lost 2,720 ± 1,390 billion tonnes of ice between 1992 and 2017, which corresponds to an increase in mean sea level of 7.6 ± 3.9 millimetres (errors are one standard deviation). Over this period, ocean-driven melting has caused rates of ice loss from West Antarctica to increase from 53 ± 29 billion to 159 ± 26 billion tonnes per year; ice-shelf collapse has increased the rate of ice loss from the Antarctic Peninsula from 7 ± 13 billion to 33 ± 16 billion tonnes per year.
The scientific community has had a vigorous debate about the stability of the west Antarctic ice sheet since 2014 when NASA and University of California, Irvine scientists said that the irreversible collapse of the west Antarctic ice sheet had started. www.jpl.nasa.gov/…
A new study by researchers at NASA and the University of California, Irvine, finds a rapidly melting section of the West Antarctic Ice Sheet appears to be in an irreversible state of decline, with nothing to stop the glaciers in this area from melting into the sea.
The study presents multiple lines of evidence, incorporating 40 years of observations that indicate the glaciers in the Amundsen Sea sector of West Antarctica "have passed the point of no return," according to glaciologist and lead author Eric Rignot, of UC Irvine and NASA's Jet Propulsion Laboratory in Pasadena, California. The new study has been accepted for publication in the journal Geophysical Research Letters.
These glaciers already contribute significantly to sea level rise, releasing almost as much ice into the ocean annually as the entire Greenland Ice Sheet. They contain enough ice to raise global sea level by 4 feet (1.2 meters) and are melting faster than most scientists had expected. Rignot said these findings will require an upward revision to current predictions of sea level rise.
"This sector will be a major contributor to sea level rise in the decades and centuries to come," Rignot said. "A conservative estimate is it could take several centuries for all of the ice to flow into the sea."
James Hansen’s paper in 2016 proposed that exponentially increasing Antarctic melt rates could cause sea level to rise 2 meters — more than 6 feet — in the next 50 to 150 years, was met with skepticism. www.atmos-chem-phys.net/… Rapid sea level rise happened at the end of the last interglacial period 120,000 years ago, when sea level rose about 6 meters, about 20 feet. However, it is hard to get precise estimates of the annual rates of sea level rise from the geologic record.
Twenty years ago scientific evidence showed that the west Antarctic ice sheet was stable. West Antarctic melting had no net effect on sea level. New snow was in balance with ice loss. science.sciencemag.org/...
Like other ice sheets, the WAIS is not a single dynamic entity: it comprises three major and several minor drainage systems (see figure) that have separate regimes and are unlikely all to accelerate at once. But as a worst-case scenario, assume that the whole WAIS behaves as a unit. The present-day outflow of ice from the WAIS is equivalent to about 1 mm/year in sea-level rise; that amount is roughly balanced by the withdrawal of water from the ocean to produce snowfall over the ice sheet. Because approximately half of the WAIS is below sea level and consequently already displaces ocean water, the increase in outflow rates needed for a rapid rise in sea level is at least a factor of 6. This large change could come about only from a massive instability. Is there theoretical or observational evidence to suggest the existence of such an instability?
This 20 year old article was not bad science. Over the past 20 years climate change has had a dramatic effect on the ocean currents around Antarctica. Increased glacial melting caused a fresh water layer to form which slowed or stopped deep water formation and insulated warm intermediate water which accelerated the rate of melting on the bottom of the ice sheet. The key instability that was not understood in 1997 was the vulnerability of the ice to melting from below. The details of submarine topography proved to be critical. Once warm ocean water was able to get past the shallow near shore submarine ridges that grounded the bottom of the ice sheet, it was able to penetrate miles inland in deep channels underlying the large outlet glaciers. This instability is possible because the weight of glacial ice has pushed the bedrock of west Antarctica hundreds of feet below sea level.
advances.sciencemag.org/…
Using a simple ocean model driven by observed forcing, we show that freshwater input from basal melt of ice shelves partially offsets the salt flux by sea ice formation in polynyas found in both regions, preventing full-depth convection and formation of DSW (Dense Shelf Water the precursor to Antarctic Bottom Water) . In the absence of deep convection, warm water that reaches the continental shelf in the bottom layer does not lose much heat to the atmosphere and is thus available to drive the rapid basal melt observed at the Totten Ice Shelf on the Sabrina Coast and at the Dotson and Getz ice shelves in the Amundsen Sea. Our results suggest that increased glacial meltwater input in a warming climate will both reduce Antarctic Bottom Water formation and trigger increased mass loss from the Antarctic Ice Sheet, with consequences for the global overturning circulation and sea level rise.
The rapid increase in Antarctic ice loss poses a difficult challenge to scientists who are trying to predict the rate of sea level rise because the rates of change are rapidly changing. What we do know is that critical facilities such as Navy Station Norfolk, the U.S. Navy’s largest facility, are already being affected by a triple whammy of natural subsidence, sea level rise and the intermittent slowing of the Gulf Stream. Cities from Houston to Miami to Norfolk Beach are already being hit by the deadly combination of rising waters and strengthening storms. And now we know it going to get rapidly worse. We just don’t know how rapidly because the climate — ocean system is too complex to predict rates accurately when so many factors affecting those rates are in rapid change.