large loss due to high pressure zone not taken into account by climate models

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I don't doubt at all that AGW is a real thing. But the sort of information the press often provides is not a very useful source of meaningful data.

Greenland has a rather large ice sheet, so I have no idea if 197 gigatonnes is a lot in that context nor not. Do you?

The meltwater canyon may be impressive, but is it meaningful? What was it like in 2010? How about 2000 or 1990, etc.? What is the context?

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  Rick C. 

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atic-

on the press often provides is not a very useful source of meaningful data.

es is a lot in that context nor not. Do you?

"Analysis of gravity data from GRACE satellites indicates that the Greenlan d ice sheet lost approximately 2900 Gt (0.1% of its total mass) between Mar ch 2002 and September 2012. The mean mass loss rate for 2008?2012 w as 367 Gt/year."

t like in 2010? How about 2000 or 1990, etc.? What is the context?

In context, 197 gigatonnes in one month looks like a lot. But Greenland is always going to lose a lot of mass in the middle of summer, and get quite a bit back in the following winter.

The interesting question about ice sheets isn't so much about how fast they are melting, as how far they are off sliding off into the ocean, which hap pens quite lot fast than melting in place.

Of course, if you melt enough of an ice sheet, the water flowing under the ice into the ocean could lubricate the flow over the bed-rock, and get the ice sheet moving a lot faster than it has in the past, but it all happens i n areas that aren't easy to look at.

James Hansen published on this back in 1916.

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Bill Sloman, Sydney

Some back of the envelope calculations:

197 Gt is about 200 km**3 or 200E9 m**3 of ice.

The total glacier area in Greenland is about 2E6 km**2 or 2E12 m**2.

That gives 0.1 m**3 / m**2 or 100 mm of ice melting on average.

Depending on area, the annual rainfall is 2 to 9 times than that.

Help, help, the sky is falling :-) :-)

On Thursday, April 16, 2020 at 6:11:12 PM UTC+10, snipped-for-privacy@downunder.com wr ote:

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Probably not yet.

The problem with the Greenland ice sheet - and the West Antarctic ice sheet - isn't about them melting in place (which would take a very long time) bu t rather when they are going to slide off into the ocean.

The extra melt-water pouring through them down to bed-rock below lubricates the glacial flow. At some point the glaciers start moving fast enough that frictional heating produces more melt-water, and you get a lot of ice slid ing into the sea in a few years.

This happened with quite few ice sheets at the end of the last ice age, and sea levels went up quite rapidly over a century or so while it was going o n for a particular ice sheet - there were several.

At some point the extra fresh water in the Northern Atlantic stopped the Gu lf Stream for 1300+/-10 years, which had an interesting effect on the clima te around the North Atlantic.

Not exactly the sky falling, but definitely attention-getting.

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Bill Sloman, Sydney

Melting land ice raises ocean levels. But rainfall does not, because it originally came from the ocean. So it's hard to learn anything from the comparison.

--
 Thanks, 
    - Win

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The comparison is how fast it is melting vs. how fast it is laid down. In Greenland much of the "rainfall" ends up as glacier.

That's why I asked about context. Is this ice melting significant in the n ormal ebb and flow of the glaciers? After all, glaciers lose ice all the t ime. Just ask the survivors of the Titanic.

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  Rick C. 

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The Greenland area is about 1 % of the total ocean surface area. If

100 mm ice melts away in Greenland, the ocean level will increase by 1 mm.

How did the Greenland and Antarctic glaciers form initially ? By comets hitting those areas ? I do not think so.

Most likely there has been a small imbalance between annual rainfall and annual melting, allowing ice buildup for a long time, which removed water from the oceans and deposited upon the glaciers.

Now it appears that at least in some years the imbalance has shifted and the melting is slightly larger than the rainfall during some years. The basic evaporation/rainfall cycle has not changed, but does the rain fall onto the same areas as before ?

The relevant question is the difference between rainfall and melting in a specific glacier.

amatic-

n Greenland much of the "rainfall" ends up as glacier.

normal ebb and flow of the glaciers? After all, glaciers lose ice all the time. Just ask the survivors of the Titanic.

The answer is no. The real problem is what hit the Titanic. When large chun ks of ice break off from the ice-sheet they end up heading towards the equa tor and melting much faster than they would have when they were part of the ice sheet,

Lots of melt-water in the ice sheet lubricates glacier flow, and more of th e ice sheet slides off as iceberg. Ice sheets don't melt in place but rathe r start sliding off into the ocean progressively faster, until there's no i ce there to slide off.

Sea level rise at the ends of ice ages isn't a smooth process - it goes up fast for a century or so as some ice sheet or other slides off into the oce an in big chunks.

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Bill Sloman, sydney

The relevant question is "how fast is the glacier sliding off into the ocean?" and whether the extra melt-water is speeding this up.

--
Bill Sloman, Sydney

The trend was 120 m rise in 8000 years from 15000 to 7000 BP.

Yes, there is a good lubrication during summer and autumn months.

What happens when the lubricant is missing during the winter ? It will increase the friction and slow down the ice, finally getting it to a stop on less tilted surfaces..

In order to have frictional bottom heating and hence lubrication during the winter, the ice must be moving (converting potential energy to kinetic energy, which is converted to heat by friction).

The ground tilt must be much larger to get the ice moving again.

In the next summer, with new lubricant, the ice starts moving even on less tilted surfaces.

On Friday, April 17, 2020 at 5:01:30 PM UTC+10, snipped-for-privacy@downunder.com wrot e:

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eet - isn't about them melting in place (which would take a very long time) but rather when they are going to slide off into the ocean.

tes the glacial flow.

Better, anyway.

ing produces more melt-water, and you get a lot of ice sliding into the sea in a few years.

The lubrication isn't missing during the winter - there's just less of it.

Some of the heat that melts the ice sheet comes up from below. The centre t he earth is rather warm, and while it have been cooling off for billions of years, there is some residual heating from long-lived radio isotopes.

o a

There's a lot of ice moving down towards the sea. It may slow down, but it isn't going to stop.

It gets pushed over the less tilted bits by the adjacent ice moving down th e more tilted bits.

Frictional heating would help, but it isn't the only heat source - and isn' t usually a significant one.

Somewhere. The upstream ice pushes on the downstream ice.

Rather, it keeps moving, but a bit faster.

and sea levels went up quite rapidly over a century or so while it was goin g on for a particular ice sheet - there were several.

Gulf Stream for 1300+/-10 years, which had an interesting effect on the cl imate around the North Atlantic.

--
Bill Sloman, Sydney

Some reality checks.

The geothermal flux through the surface is below 0.1 W / m**2. Compare this to the 1000 W/m**2 solar flux.

To melt 0 C ice to 0 C water requires 333 kJ/kg. To melt 1 mm layer from the bottom of a 1 m **2 of ice column requires melting 1 kg of ice or 333 kJ. With less than 0,1 W available, this requires more than a month to create1 kg lubricant water, assuming no heat losses through the ice.

Clearly, the geothermal heat is completely insignificant in lubricating the bottom of the glacier.

There are hundreds or thousands of things not taken into account by climate models. One candid modeler said that not only don't we know the magnitudes of many causalities, we don't know the signs.

--

John Larkin         Highland Technology, Inc 

Science teaches us to doubt. 

  Claude Bernard

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That would be James Arthur's acquaintance, who didn't seem to be very good at it and went off and did something else.

John Larkin won't be able to name a single one of those "hundreds or thousa nds of things not being taken into account" but he could probably find the link to the climate change denial website where he read read the line.

He's a gullible twit, and that explains pretty much everything he writes ab out climate change.

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Bill Sloman, Sydney

Since the albedo of fresh snow can be as high as 0.85, as little as 150 W/m**2 of that solar flux can end up in the surface, and most of it gets re-radiated away at night.

At the bottom of the ice sheet, the heat and the meltwater it produces do stick around.

As I said, the lubrication isn't missing in winter, there's just less of it.

The ice sheet is a mile or so thick, so the heat loss through it is pretty slow.

What makes you think that? And does it matter? Glaciers keep on flowing down to the sea all through the year.

The point I was originally making is that they do speed up from time to time, and lots of melt-water does appears to help that.

If you want weird things in ice sheets read up on Dansgaard-Oeschger cycles,

and Bond events

They seem to be rather complicated structures.

--
Bill Sloman, Sydney

On Friday, April 17, 2020 at 7:36:12 AM UTC-4, snipped-for-privacy@downunder.com wrote :

rote:

f

-dramatic-

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sheet - isn't about them melting in place (which would take a very long ti me) but rather when they are going to slide off into the ocean.

icates the glacial flow.

eating produces more melt-water, and you get a lot of ice sliding into the sea in a few years.

t.

e the earth is rather warm, and while it have been cooling off for billions of years, there is some residual heating from long-lived radio isotopes.

A liter of water spread over a square meter doesn't sound insignificant to me. That would be a layer 1 cm thick, no?

It's not clear just what the need is to facilitate movement of the ice abov e. Given the roughness of the ground or maybe the lack of roughness given the ages it has been under the ice, a cm may be perfectly adequate to facil itate movement. I know I slip and fall from a layer of melted ice much thi nner than a cm. Much, much thinner.

If ice is slippery from your weight causing a melted layer of water, why do esn't that layer of water freeze your foot to the ice as you lift the press ure???

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  Rick C. 

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The volume of a 1 m x 1m x 1 cm is 100 cm x 100 cm x 1 cm, is 10000 cm**3 or 10 dm**2 or 10 liters and the mass is 10 kg.

1 kg of ice is a 1 mm thick layer, requiring 333 kJ to melt.

If you really want an example of geothermal heat causing glacier flow, take a look at

in which a vulcan erupted under a glacier, but that was on Iceland.

On Friday, April 17, 2020 at 1:44:47 PM UTC-4, snipped-for-privacy@downunder.com wrote :

ote:

r of

irm-dramatic-

**2. . .

ice sheet - isn't about them melting in place (which would take a very long time) but rather when they are going to slide off into the ocean.

ubricates the glacial flow.

l heating produces more melt-water, and you get a lot of ice sliding into t he sea in a few years.

f it.

ntre the earth is rather warm, and while it have been cooling off for billi ons of years, there is some residual heating from long-lived radio isotopes .

to me. That would be a layer 1 cm thick, no?

bove. Given the roughness of the ground or maybe the lack of roughness giv en the ages it has been under the ice, a cm may be perfectly adequate to fa cilitate movement. I know I slip and fall from a layer of melted ice much thinner than a cm. Much, much thinner.

doesn't that layer of water freeze your foot to the ice as you lift the pr essure???

You are right. I did the math pictorially in my head by seeing a liter as a cubic dl and thinking it could be spread over the meter by 1 meter area, but didn't do it right. I'll have to work on the projector right after I f ix my laptop hinge and keyboard.

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  Rick C. 

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