Predicting sea level rise: Understanding how icebergs form could lead to better forecasts

Nov 23, 2010
A helicopter view of a crack in the Amery Ice Shelf in East Antarctica that has been propagating at about 3 meters per day for close to two decades. Eventually, this crack system is expected to yield an iceberg. Photo by Jim Behrens

(PhysOrg.com) -- In an effort to understand how fast sea level could rise as the climate warms, a University of Michigan researcher has developed a new theory to describe how icebergs detach from ice sheets and glaciers.

This process of "iceberg calving" isn't well understood. While scientists believe it currently accounts for roughly half of the mass lost in shrinking ice sheets, current models don't take changes in iceberg calving into account in their predictions, says Jeremy Bassis, an assistant professor in the Department of Atmospheric, Oceanic and Space Sciences.

Bassis is the author of a paper on the new theory published online today in the . It will appear in print in the January edition.

"Our models cannot predict about half of the mass balance. We don't know how much of an effect this will have, but we've seen several prominent examples where calving is connected with speed-up of the ice-retreat process," Bassis said.

The Larsen B ice shelf in Antarctica—a 2,000-square-mile, 700-foot-thick slab that had been stable for thousands of years—disintegrated in about six weeks between January and March of 2002. Scientists believe rising temperatures and ice fracturing primarily caused the disintegration. But they don't have a handle on exactly how it happened.

When ice breaks off of ice shelves, it doesn't directly or immediately cause melting and sea level rise. But scientists believe it can contribute to and hasten those processes. The icebergs can float into warmer parts of the ocean and melt. And ice calving can perhaps lead to more fracturing.

"What we've been lacking is a way to quantify whether calving will increase or decrease in the future, and do it in a way that doesn't involve information from a particular glacier. There are thousands and thousands of glaciers that might break up because of change. We'd like to have a theory that explains how this happens for any regime and this is a step in that direction," Bassis said.

Bassis' theory is a statistical methodology that allows him to predict the average iceberg calving rate and how much that can be expected to fluctuate for a given region based on the amount of stress within the ice and its thickness. He was able to construct a more general model than current ones, he says, because he assumed that cracking happens somewhat randomly. He didn't try to predict where every fracture would occur.

"You don't need to understand what every glacier is doing if you know what are doing on the whole," Bassis said.

Current predictions of sea level rise range from about four inches to 2.5 feet by 2100. This is a wide range that Bassis' theory could help to narrow.

"From a societal perspective, a significant portion of the Earth's population lives very close to sea level. We'd like to be able to better predict how much sea level will rise so we can build defenses or, if necessary, plan for migrations," Bassis said.

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More information: The paper is called "The statistical physics of iceberg calving and the emergence of universal calving laws." www.igsoc.org/journal/57/201/

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User comments : 7

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NotParker
2 / 5 (4) Nov 23, 2010
The sea level isn't rising any more than it has for thousands of years.
jamesrm
3.7 / 5 (3) Nov 24, 2010
"The sea level isn't rising any more than it has for thousands of years."

Thanks all my fears are assuaged, praise NotParker for his deep knowledge and well expounded critique of the current paradigm

rgds
knotfcuknuckle
NotParker
2.3 / 5 (3) Nov 24, 2010
Take a look at the grpah of the last 8000 years.

http://pustakalay....png.htm

And guess what ... the sea level will gradually rise until it stops and then it will stop rising as the end of this interglacial approaches and we plunge into the rest of this ice age.

It will get about 10C cooler, pretty much ending agriculture in large parts of the earth.

Take a look at the bottom graph:

http://joannenova...e-graph/

3432682
3 / 5 (4) Nov 24, 2010
NotParker, you are a subversive, resorting to facts. Shame on you.
jamesrm
2.3 / 5 (3) Nov 24, 2010
Quote from an Aussie journalist who worked for Murdock is not a source of science, might as well qoute Palin or any other schill on Fox News :)

rgds
notafcuknuckle
jamesrm
2.3 / 5 (3) Nov 24, 2010
www.skepticalscie...ook.html

"Not long ago, I read the Skeptics Handbook which displays some fundamental misunderstandings of how our climate works. I wondered whether a rebuttal of this document would be worthwhile but when I floated the idea to a few people, the general response was "been there, done that". ...

"The 'Skeptics Handbook' begins by asking "what evidence is there that more CO2 forces temperatures up further?" It then lays out 4 arguments: the greenhouse signature is missing, CO2 lags temperature, it's not warming and the CO2 effect is saturated. The great irony of the 'Skeptics Handbook' is when you examine these 4 arguments and the full body of empirical evidence that goes with them, what you actually find is the evidence that more CO2 forces temperatures up further.

rgds
notafcuktard
GSwift7
1 / 5 (1) Nov 26, 2010
This is a little dangerous in principle. In the title of the paper he uses the term "statistical physics", which is what he is proposing here since theoretical physics can't predict glacier processes very well (if I'm reading it correctly).

In a chaotic system like those involved in thermodynamics, it seems entirely appropriate to use statistical physics to be able to predict the behavior of a system. It's been demonstrated that the statistically derived laws of thermodynamics produce a good predictive model of many systems under many circumstances. I'm not sure you can do that with ice bergs with as much confidence. How do you verify the efficacy of the statistical model? Can you test it in an isolated way over a meaningful time span? Can/should the model be used before it is verified by testing?