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THE Glacier Thread (merged)

Re: Greenland ice sheet lowered six metres in just a month

Unread postby vtsnowedin » Sun 01 Aug 2010, 12:55:16

8) Well we will of of course assume that the region they were in was typical of the whole ice cap and that this is the new norm so lets say that the summer melt season is effectively two months long netting a twelve meter per year loss. So 3000 meters of ice divided by twelve would mean that it will be all gone by 2260 plus or minus a decade or two.
Other things may become more important in the mean time.
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Re: Greenland ice sheet lowered six metres in just a month

Unread postby timmac » Sun 01 Aug 2010, 17:05:22

Great news, this means the Pacific will be closer to Vegas....

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Re: Greenland ice sheet lowered six metres in just a month

Unread postby Keith_McClary » Sun 01 Aug 2010, 19:51:54

vtsnowedin wrote:8) Well we will of of course assume that the region they were in was typical of the whole ice cap and that this is the new norm so lets say that the summer melt season is effectively two months long netting a twelve meter per year loss. So 3000 meters of ice divided by twelve would mean that it will be all gone by 2260 plus or minus a decade or two.

The area of the oceans is 200 times that of the Greenlandic sheet, so every 2 meters of melt is one cm of sea level.
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Re: Greenland ice sheet lowered six metres in just a month

Unread postby Lore » Sun 01 Aug 2010, 19:58:15

John Cook's Skepticalscience.com has a current post on the melting of the Greenland ice cap. As usual a rather good rundown.

The Greenland ice sheet has a negative mass balance, meaning that it is losing ice (Velicogna 2009, Jiang 2010). This loss occurs because the gain of new ice (in the form of snowfall within the ice sheet's interior zone of accumulation) cannot keep up with the rapid loss of ice through melting and the discharge of ice by marine terminating outlet glaciers (van den Broeke 2009).

In conclusion, a pessimistic but reasonable scenario would produce the melting of somewhere around 5% of the Greenland ice sheet by 2100, contributing 16 to 54 cm to global sea level rise (which in turn would then total 80 cm to 2 m from all sources). However, at that point the collapse of Greenland's ice sheet would just be getting started - failure to constrain CO2 concentrations below 400-560 ppm would almost certainly lead to the near-total loss of the ice sheet, as we have seen from both model results and comparison to the MIS-11 interglacial climate of 400,000 years ago.

http://www.skepticalscience.com/past-an ... sheet.html
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Re: Greenland ice sheet lowered six metres in just a month

Unread postby hillsidedigger » Sun 01 Aug 2010, 21:57:19

It does not all need to all melt to be a big deal for at some point during the melting process you can bet that a big chunk (thousands of cubic miles) will suddenly slide into the ocean.
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Re: Greenland ice sheet lowered six metres in just a month

Unread postby vtsnowedin » Sun 01 Aug 2010, 22:08:26

hillsidedigger wrote:It does not all need to all melt to be a big deal for at some point during the melting process you can bet that a big chunk (thousands of cubic miles) will suddenly slide into the ocean.

That's highly unlikely as most of the island is ringed by a high ridge of mountains that act as a dam to the flow of ice to the sea.
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Re: Greenland ice sheet lowered six metres in just a month

Unread postby dissident » Sun 01 Aug 2010, 22:35:55

It does not all need to all melt to be a big deal for at some point during the melting process you can bet that a big chunk (thousands of cubic miles) will suddenly slide into the ocean.


Exactly. What model are they using to estimate 16 to 54 cm of sea level rise by 2100? The story of the last few years is that ice sheet dynamics is poorly understood. The default mode for human thinking be it scientific or not is implicit linearization. There is no sense of the rapid nonlinear processes that can develop in natural systems. Unlike for fluid dynamics the ice sheet models do not have a "simple" set of equations. Do they really have detailed finite volume codes that follow every crack in the Greenland ice sheet and are able to respond properly to the propagation of new cracks along with water flow from the surface? They don't even have observations of the 3D distribution of the ice sheet. Judging by what is presented they are still heavily reliant on crude parameterizations and not first principles treatment of the problem.

This is better than nothing, but I wouldn't trust the 54 cm upper bound on the sea level rise contribution.
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Himalayan glaciers spell trouble for climate scientists

Unread postby Serial_Worrier » Thu 27 Jan 2011, 21:43:17

http://www.telegraph.co.uk/earth/enviro ... tists.html

The abject admission by the official Intergovernmental Panel on Climate Change (IPCC) a year ago that it made a mistake, in its latest report, in predicting their disappearance by 2035 marked the lowest point in their reputation - and they have still far from recovered.
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Re: Himalayan glaciers spell trouble for climate scientists

Unread postby eXpat » Thu 27 Jan 2011, 22:42:52

Same article:
And climate sceptics are bound to seize on today's news that more than half the glaciers in the Karakoram mountains in the west of the world's highest chain are either stable or actually advancing as providing dramatic evidence that global warming is not taking place. But it does no such thing.

For a start, the study that made the discovery concluded – as lead researcher Dirk Scherler put it that - "overall in the Himalayas, the glaciers are retreating". What made the difference in the Karakoram was that many are covered in a layer of rubble that has eroded from the peaks, insulating the ice from the warmth of the sun. Where this layer was present the glaciers did not melt or even grew; where it was not the rate of retreat remained high.

Elsewhere in the world the retreat continues. Just last weekend, for example, it was announced that Greeenland's icesheet melted at a record rate in 2010 and studies show that most of the world's glaciers are shrinking.
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Re: Himalayan glaciers spell trouble for climate scientists

Unread postby eXpat » Thu 27 Jan 2011, 23:25:51

All models are and can be constantly perfected, what there´s no doubt about is the final outcome.
Some Himalayan glaciers advance, despite warming
(Reuters) - Some Himalayan glaciers are advancing despite an overall retreat, according to a study on Sunday that is a step toward understanding how climate change affects vital river flows from China to India.

A blanket of dust and rock debris was apparently shielding some glaciers in the world's highest mountain range from a thaw, a factor omitted from past global warming reports. And varying wind patterns might explain why some were defying a melt.

"Our study shows there is no uniform response of Himalayan glaciers to climate change and highlights the importance of debris cover," scientists at universities in Germany and the United States wrote in the study of 286 glaciers.

The findings underscore that experts in the U.N.'s Intergovernmental Panel on Climate Change (IPCC) were wrong to say in a 2007 report that Himalayan glaciers could vanish by 2035 in a headlong thaw. The panel corrected the error in 2010.

The report said that 58 percent of glaciers examined in the westerly Karakoram range of the Himalayas were stable or advancing, perhaps because they were influenced by cool westerly winds than the monsoon from the Indian Ocean.

Elsewhere in the Himalayas "more than 65 percent of the monsoon-influenced glaciers ... are retreating," they wrote in the journal Nature Geoscience of the satellite study from 2000 to 2008. Some glaciers that were stable in length were covered by a thick layer of rocky debris.

"Overall in the Himalayas, the glaciers are retreating," Dirk Scherler, the lead author at the University of Potsdam in Germany, told Reuters.

ALPS TO ANDES

Scherler said the findings did not allow the experts to make any new estimates of water losses from Himalayan glaciers, whose seasonal melt helps keep up flows in the dry season in rivers from the Ganges to the Yangtze. More study was needed, he said.

"Glaciers are important to water supply to many people living in lowlands, not only for food and drinking water but also for hydropower," Scherler said. "It's essential to know what's going on."

Worldwide, most glaciers are shrinking from the Alps to the Andes in a trend blamed by the IPCC on greenhouse gases from human activities, led by the burning of fossil fuels.

Debris in the Himalayas -- darker than ice and so soaking up more of the sun's energy -- tended to quicken a thaw if it was less than 2 cms (0.8 inch) thick. But a thicker layer on some Himalayan glaciers acted as insulation, slowing the melt.

Among complexities, some debris-covered glaciers that are stable in length might be getting thinner and so losing water overall, he said. That trend had been shown by past studies of the Khumbu glacier on Mount Everest, for instance.

http://www.reuters.com/article/idUSTRE70M1RC20110123
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Re: Greenland ice sheet lowered six metres in just a month

Unread postby Tanada » Sat 29 Jan 2011, 08:40:13

ScienceDaily (Jan. 21, 2011) wrote:This past melt season was exceptional, with melting in some areas stretching up to 50 days longer than average," said Dr. Marco Tedesco, director of the Cryospheric Processes Laboratory at The City College of New York (CCNY -- CUNY), who is leading a project studying variables that affect ice sheet melting.

"Melting in 2010 started exceptionally early at the end of April and ended quite late in mid- September.

http://www.sciencedaily.com/releases/20 ... 144011.htm

Looks to me like the evidence of thawing continues to grow, unlike the ice sheet itself.
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Re: Greenland ice sheet lowered six metres in just a month

Unread postby Daniel_Plainview » Sat 29 Jan 2011, 10:20:41

Lore wrote:
However, at that point the collapse of Greenland's ice sheet would just be getting started - failure to constrain CO2 concentrations below 400-560 ppm would almost certainly lead to the near-total loss of the ice sheet


Assuming a linear increase from our current 390 ppm, we'll be at 400 ppm in a few years; assuming a parabolic / exponential increase (given methane release + feedbacks), we could be at 500-600 ppm in a few years.

... Might be time to sell your ocean-front property ...
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Re: Greenland ice sheet lowered six metres in just a month

Unread postby scas » Sat 29 Jan 2011, 11:26:00

Don't know if many of you have had time to read Hansen's recent paper, but I believe he is calling for up to 5 metres of sea level rise now with periods of non-linearity.
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Re: Greenland ice sheet lowered six metres in just a month

Unread postby Homesteader » Sat 29 Jan 2011, 11:39:37

Daniel_Plainview wrote:Assuming a linear increase from our current 390 ppm, we'll be at 400 ppm in a few years; assuming a parabolic / exponential increase (given methane release + feedbacks), we could be at 500-600 ppm in a few years.


Just took a look at the ERSL data for Svalbard. Most recent CO2 measurements are right at 395 ppm. Up 2-3 ppm from the same time last year.
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Re: Greenland ice sheet lowered six metres in just a month

Unread postby Daniel_Plainview » Sat 29 Jan 2011, 11:50:07

Homesteader wrote:
Daniel_Plainview wrote:Assuming a linear increase from our current 390 ppm, we'll be at 400 ppm in a few years; assuming a parabolic / exponential increase (given methane release + feedbacks), we could be at 500-600 ppm in a few years.


Just took a look at the ERSL data for Svalbard. Most recent CO2 measurements are right at 395 ppm. Up 2-3 ppm from the same time last year.


Homesteader, do you have a link showing 395 ppm?
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Re: Greenland ice sheet lowered six metres in just a month

Unread postby Homesteader » Sat 29 Jan 2011, 12:00:16

http://www.esrl.noaa.gov/gmd/dv/iadv/gr ... gg&type=ts

click on previous full year of data, click submit
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Re: Greenland ice sheet lowered six metres in just a month

Unread postby PrestonSturges » Sat 29 Jan 2011, 12:17:44

vtsnowedin wrote:
hillsidedigger wrote:It does not all need to all melt to be a big deal for at some point during the melting process you can bet that a big chunk (thousands of cubic miles) will suddenly slide into the ocean.

That's highly unlikely as most of the island is ringed by a high ridge of mountains that act as a dam to the flow of ice to the sea.

What was the prehistoric event where the inland glacial sea collapsed in ancient America/Canada, creating a flood that erased several states and left sediment hundreds of feet deep?

We wouldn't see it in our lifetimes, but there have been multiple events in the recent geologic past where entire seas went rampaging across the landscape.

It would be interesting if sea level rose a two feet more or less overnight.
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Re: Greenland ice sheet lowered six metres in just a month

Unread postby vtsnowedin » Sun 30 Jan 2011, 10:20:01

PrestonSturges wrote:
vtsnowedin wrote:
hillsidedigger wrote:It does not all need to all melt to be a big deal for at some point during the melting process you can bet that a big chunk (thousands of cubic miles) will suddenly slide into the ocean.

That's highly unlikely as most of the island is ringed by a high ridge of mountains that act as a dam to the flow of ice to the sea.

What was the prehistoric event where the inland glacial sea collapsed in ancient America/Canada, creating a flood that erased several states and left sediment hundreds of feet deep?

We wouldn't see it in our lifetimes, but there have been multiple events in the recent geologic past where entire seas went rampaging across the landscape.

It would be interesting if sea level rose a two feet more or less overnight.

You have as much access to google and wiki as I do. :) There were two events similar to what your alluding to. The first was the glacial lake Hebert IIRC that was the backed up Connecticut river behind a moraine dam at Rocky Hill Conn.The lake extended as far north as Haverhill New Hampshire and up the White river valley to Bethel VT. You can still see the alluvial out-wash plains on the sides of the valley in Royalton VT. some fifty feet above the present valley floor. I'm not sure when the moraine eroded away and let the water out suddenly. Perhaps eight or ten thousand years ago. The other has a name that I do not recall and was a much larger lake held back by the ice clogging what is now the St. Lawrence river. The backup would have covered western VT ,upstate NY. and parts of Ohio, Quebec and Ontario, The sediments that didn't wash out to sea would have to be on the flood plains of the St. Lawrence east of Montreal which is some very flat and rich farmland. I don't know which let out first or if the washout from the Connecticut caused any climate change that we have been able to detect.
That's all I know on the subject without resorting to Wiki.
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Re: Greenland ice sheet lowered six metres in just a month

Unread postby dohboi » Sun 30 Jan 2011, 22:14:37

Are you thinking of Lake Agassiz? That was supposed to have suddenly drained north into Hudson Bay about 13000 BP (ok, I checked wiki for the date:http://en.wikipedia.org/wiki/Lake_Agassiz
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Re: Greenland ice sheet lowered six metres in just a month

Unread postby Serial_Worrier » Mon 31 Jan 2011, 00:46:40

Oh please, stop panicking everyone about a non-event. 8)
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