... the Antarctic ice sheet is now losing 159 billion tonnes of ice each year – twice as much as when it was last surveyed.
... these newly measured losses from Antarctica alone are enough to raise global sea levels by 0.45 mm each year.
... the increased thinning we have detected in West Antarctica is a worrying development,' said Professor Shepherd. [emphasis mine]
New research on the impact of increasing Westerlies indicates that Antarctic Ice Sheet Melt may be even faster than 3 meters over 200 -500 years. Add a few tenths of a meter of sea level rise this century, for starters.
Sea levels may rise much faster than predicted because climate models have failed to account for the disruptive effects of stronger westerly winds, Australian-led research has found.
Recent studies of Antarctica have suggested the giant glaciers of West Antarctica may have begun an irreversible melting that will raise sea levels by as much as 3 metres over 200-500 years.
That estimate, though, may prove optimistic because models had failed to account for how strengthening westerly winds in the Southern Ocean would start to impinge coastal easterlies, upsetting a delicate balance of warm and cold waters close to the Antarctic ice sheets, said Paul Spence, an oceanographer at the University of NSW’s Climate Change Research Centre.
“It’s the first time that I looked at my science and thought, 'Oh my god, that is very concerning'!”, he said. “You hope it’s wrong and you hope it doesn’t happen.
The research, published in Geophysical Research Letters, found that the coastal temperature structure was more sensitive to global warming, particularly the changes to winds, than previously identified.
“The dynamic barrier between cold and warm water relaxes, and this relatively warm water just offshore floods into the ice-shelf regions, increasing the temperatures by 4 degrees under the ice shelf,” he said.
“If you look at how sensitive the coastal ocean is to these changing winds, you could put a lot more heat under these ice shelves than people have previously thought,” Dr Spence said.
The new modelling shows it doesn’t take much additional wind to the system “to really, dramatically upset" conditions, he said. “It’s a system really dramatically ripe for change.”
“This paper is a necessary first step to actually closing some the understanding gaps,” Dr van Ommen said.
While predictions of future sea-level rise were difficult to make, “adding a few tenths of a metre from ice instability this century is a significant concern”, he said. [emphasis mine]
A new study found that, at the end of the last ice age, Antarctica responded quickly to ocean warming with large glacial outburst floods.
... the paper found an Antarctic ice sheet that was very sensitive to warming.
Now that humans are warming the atmosphere and oceans at a pace at least 30 times that of the last ice age, we are discovering that Antarctica in the deep past showed a major destabilization response to even the slightest hint of warming.
... we should consider that start time for glacial destabilization and increasing rates of sea level rise to be now and not in some distant, far off, future. Glacial systems may well present considerable atmospheric inertia. But when presented with warming waters, the glaciers must yield. This makes sense as water’s heat capacity is four times greater than that of air. So the melting force of water just one degree C above freezing is about four times that of the same volume of air at the same temperature.
... sea level rise for the current century is likely to be far greater than previously anticipated by scientific assessments. The top range of a 3 foot sea level rise for this century under IPCC modeling is likely, given current realities, to instead be a low estimate. A more realistic range, given a greatly reduced true glacial inertia, is probably 3-9 feet through 2100 with higher outside potentials during large glacial outburst flood events. [emphasis mine]
We assumed that Antarctic glaciers would pose great inertia to warming, perhaps based on experience with resistance of land-bound glaciers to warmer air. Now scientists realize Antarctica's vulnerability to warm water. Within decades even the public will appreciate the folly of dumping excess Anthropogenic heat into the oceans.
Greenland is losing twice as much ice as 5 years ago too.
A new study finds that both the Greenland ice sheet and West Antarctic Ice Sheet (WAIS) have seen an astonishing increase in ice loss in just the past five years.
Comparing the current CryoSat-2 data with “those from the ICESat satellite from the year 2009, the volume loss in Greenland has doubled since then.”
So we are at record rates of ice loss now. What is particularly stunning is that a major international study found in 2012 that Greenalnd’s ice loss was up by a factor of five since the mid-90s, while Antartica’s was up 50 percent in the prior decade.
We are seeing ice sheet loss at rates not imagined even a few years ago.
When hydrofracturing of ice sheets is added to models, the West Antarctic Ice Sheet melts within decades rather than centuries.
In response to atmospheric and ocean temperatures typical of past warm periods, floating ice shelves may be drastically reduced or removed completely by increased oceanic melting, and by hydrofracturing due to surface melt draining into crevasses. Ice at deep grounding lines may be weakened by hydrofracturing and reduced buttressing, and may fail structurally if stresses exceed the ice yield strength, producing rapid retreat. Incorporating these mechanisms in our ice-sheet model accelerates the expected collapse of the West Antarctic Ice Sheet to decadal time scales, and also causes retreat into major East Antarctic subglacial basins, producing ∼17 m global sea-level rise within a few thousand years. [emphasis mine]
Taking solid to solid friction into account, ice sheets will melt faster than we'd thought.
A new study finds that incorporating Coulomb friction into computer models increases the sensitivity of Antarctic ice sheets to temperature perturbations driven by climate change.
many earlier models of ice sheet dynamics tried to simplify calculations by assuming that ice loss is controlled solely by viscous stresses, that is, forces that apply to "sticky fluids" such as honey--or in this case, flowing ice. The conventional models thus accounted for the flow of ice around obstacles but ignored friction. "Accounting for frictional stresses at the ice sheet bottom in addition to the viscous stresses changes the physical picture dramatically," Tsai says.
In their new study, Tsai's team used computer simulations to show that even though Coulomb friction affects only a relatively small zone on an ice sheet, it can have a big impact on ice stream flow and overall ice sheet stability.
for any given increase in temperature, the model predicts a bigger change in the rate of ice loss than is forecasted in previous models.