From the UNIVERSITY OF KANSAS
LAWRENCE — A just-published paper in Science changes the formula scientists should use when estimating the speed of huge ice sheets in Greenland and Antarctica that flow into the ocean and drive mounting sea levels around the globe.
The change in the formula for predicting ice flow — or basal sliding — reduces “the largest uncertainty” in predicting future sea-level rise. It was prompted by analyzing data from 140 glaciers in Greenland.
University of Kansas researchers Leigh Stearns, associate professor of geology and research scientist at the Center for Remote Sensing of Ice Sheets, and Cornelis van der Veen, professor of geography, discovered friction — or “basal drag” — between ice sheets and the hard bed underneath has no influence on how fast glaciers flow.
This finding throws out a notion that has colored estimates of glacier speed for decades.
“Basal sliding is one of the most important things we try to measure in glaciology and one of the hardest to measure,” said Stearns. “Our paper says the parameter most used in ice sheet models is incorrect — the Weertman model — developed in the 1950s based on a theoretical framework that how fast ice moves at the bed is based on friction and the amount of water at the bed. We’re saying that friction doesn’t matter.”
Instead, the KU researchers found subglacial water pressure, the water pressure between the bottom of the ice sheet and the hard bed underneath, controls the speed of the ice flow.
Part of their work included an analysis of decades-old studies of water pressure underneath mountain glaciers, which “have been largely overlooked by the glaciological community.” Stearns and van der Veen paired the mountain-glacier results with the recent observations on surface velocity from the outlet glaciers in Greenland.
“We can calculate the friction at the bed of glaciers by investigating spatial patterns of surface velocity. Surprisingly, we found that the two are not at all correlated. Pressure is different and much harder to measure. We know what the pressure at the terminus is because the glacier is floating there, and we can calculate up-flow pressure based on ice thickness. It’s not a perfect estimate, but it gives us a good first approximation. If we could, we’d love to put boreholes into all 140 glaciers around Greenland and measure water pressure directly, but that’s not practical.”
Stearns and van der Veen found the relationship between subglacial water pressure in Greenland’s outlet glaciers lined up with measurements taken from the mountain glaciers in the 1980s, implying the processes for sliding variations are also similar.
“The simplified sliding relation can appropriately reproduce spatial patterns of ice velocity,” the KU researchers said. “This is in stark contrast to current modeling techniques, which involve tuning the sliding parameter in order to match observed velocities.”
“Models that are used to predict sea-level change are inexact because we can’t directly measure processes happening at the bed,” Stearns said. “Current models using Weertman solutions require tuning to match observations. It’s an imperfect way of doing what has to be done to come up with estimates. It has a lot of knobs. With this new parameter, we’re trying to reduce the amount of tuning needed.”
Even though “people were waiting for someone to challenge Weertman, people knew it needed to be improved,” Stearns said she worried about causing upset with scientists who’d relied on the older model for earlier research.
“I was a little nervous,” she said. “I was anxious because it negates what people have been using for a while. It calls into question the model they’re using. But the reaction has been positive so far. People have been encouraging of a new systematic approach to a sliding law.”
Stearns has too much humility to dub her new formula the “Stearns model,” even though it improves and replaces the less accurate “Weertman model,” named after the scientist who devised it.
She stressed her revised formula is part of the self-correcting nature of scientific inquiry and shouldn’t shed doubt on climate science or the inexorable rise of sea levels around the world as more ice from Greenland and Antarctica melts into the ocean.
“I hope it helps people believe in our projections,” she said. “This is based more on physical processes and less on things you have to tune for any reason. Anything that’s improving how we model ice sheets in the future is a good thing — how are ice sheets responding to climate change? With these model improvements, we’re getting a step closer to a really accurate understanding.”
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The paper: http://science.sciencemag.org/content/early/2018/06/06/science.aat2217
Whatever isostatic correction is made for Antarctic ice gain and loss over the Holocene, and the response of the landmass to these changes, must be a difficult task requiring knowledge of what happened in Antarctica over the Holocene.
For instance, Weaver et al 2003:
http://home.sandiego.edu/~sgray/MARS350/deglaciation.pdf
show that 14,600 years ago there was a huge ice sheet collapse in Antarctica, which by then had been steadily warming under obliquity forcing for about 5000 years. This gave rise to what is called Meltwater Pulse 1A (MPW 1a), which caused 20m of sea level rise in about 500 years, and initiated the Bolling-Allerød D-O-like warm spike (followed in reaction by the Younger Dryas).
So clearly around Holocene inception there was a big loss of land ice from Antarctica. However over the course of the Holocene the warmer moist atmosphere caused more snow, so at some point Antarctic land ice loss (as evidenced by mwp 1a) would have reversed to ice gain from all that snow.
Presumably the Antarctic land mass responded to more ice by being pushed down and to less ice by springing back up. If one wants to make an isostatic correction for Antarctica one needs to know reasonably accurately the history of land ice loss then gain over the whole Holocene inception and Holocene. I’m not sure that the state of this knowledge is good enough to allow this. This all adds a significant question mark to Antarctic isostatic adjustment, which is unfortunate in regard to both Antarctic ice volume changes and sea level, which require this adjustment to be very accurate since both metrics are in fact little more than derived factors of isostatic adjustments.
That theory is more or less dead. The problem with deriving MWP-1A from Antarctica is that an “ice collapse” would have left fresh abandoned end moraines on nunataks higher than the present ice-levels.
There isn’t any. Such higher moraines that do exist are almost invariably very old, even Pliocene or Miocene. The current Antarctic ice is about as thick as it has ever been in the Pleistocene. What happened at the end of the last ice age in Antarctica is that rising sea-levels caused flat, marginal marine-based ice sheets to retreat (an ice-front in deeper water than c. 500 meters is mechanically unstable).
What happened at the end of the last ice age in Antarctica is that rising sea-levels caused flat, marginal marine-based ice sheets to retreat (an ice-front in deeper water than c. 500 meters is mechanically unstable).
And this caused a melt-water pulse?
If the rising sea levels caused, rather than were caused by, Antarctic melt, the result is the same – a pulse of meltwater that indirectly caused the excursion of the AMOC giving rise to the Bolling-Alerod. (I had wondered why a catastrophic melt event would make sea levels rise over 500 years – one would expect a shorter timescale. Thus your explanation is more plausible.)
“Everything we said before is wrong, but you should trust us now.”
There should be an easy way to find all of the comments I have posted.
Science advances, one correction at a time.
But “science” is NOT accepting the corrections and is therefore NOT advancing in the case of climate change.
I use a global search for my name.
Let me apply a little common sense to the climate change argument. Please point out where common sense fails me.
Stipulated that the dire results of climate change will take place in the next 50 to 100 years. (Note that this is AFTER the death of most of the “scientists” doing the research so there will be no opportunity to publicly embarrass them.)
1. “We” have known about these dire consequences for several decades even though “we” are only now able to predict them with precision.
2. Much of civilization’s buildings and infrastructure have been built or rebuilt in those decades. World Population 1975 4.1 Billion vs 2015 7.4 Billion
So, which idiots have either rebuilt in the EXACT same locations that were destroyed by climate change, or built new structures withOUT taking into consideration the “dire results” of climate change?
Seems like common sense would have led all these “brilliant” scientists, city planners, architects and engineers to:
1. Move their projects out of the “danger zones” such as the coast and flood zones.
2. Designed their projects so that even a massive 1 or 2 foot rise in water levels wouldn’t affect them.
3. Would have advised AGAINST even doing the projects in an effort to reduce the SIZE of the human population to counter climate change by making life unpleasant.
Yet, here they are, building structures that will be destroyed by the inevitable change in climate.
Have I missed something? Has common sense failed me?
Common sense looks in tact to me, Mitchell.
I suspect that one reason the cliffs, low-lying coasts, and flood plains are getting built up is that older, and wiser generations avoided obviously dangerous places. Then, people with more dollars than cents, and greedy developers, built on the land formerly rejected because it was available and relatively cheap. The real tragedy is that the people making unwise decisions about where to live, expect everyone else to bail them out when their homes get destroyed.
It would be nice if they had some experimental data to validate their model.
As I recall from freshman physics, and geology 101; we spent a lot of time on friction, and slip/slump/slide.
I don’t see how friction or fundamental geology would not apply to glaciers, and their propensity to move or not.
God, have we had it up to here with rattling tins for more funding of climate models, or what? Climate is chaos. Chaos is climate. Chaos is unpredictable. Live with it and keep your hands off our wallets.
Here’s an example of the mindset of climate modellers nowadays. Remember the legendary John Daly, intrepid climate sceptic? Sea levels were his specialty. Some years ago a “peer reviewed” paper, awash with data and fancy analyses, produced a graph showing the trend in sea levels (rising, of course) from historical times to some scary point in the future. But the historical part mismatched cold hard measurements, that Daly had reported, by a country mile. When I pointed this out on the publisher’s website, the authors’ answer was that Daly’s data were clearly invalid outliers and therefore disregarded. It’s so long ago that I can’t remember essential details of the paper but maybe readers can help.
Another example in a related vein is a report, maybe about 2 years ago, of widespread famine caused by global warming, diametrically opposed to the observed reality to the contrary. Only after the report had been brandished and broadcast widely by the MSM did it sink in that the report was based on modelling! Again, just lazy about googling I suppose, but can’t recall the details.
If we could, we’d love to put boreholes into all 140 glaciers around Greenland and measure water pressure directly, but that’s not practical.”
Well, practical they could bore holes in ice cubes.
Practical. Studies or not, same outcome.