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Ice sheets and dust

Lord of Planar said:
Various studies have clean snow albedo generally around 0.85 to 0.9, or more, and changing to as low as 0.5 with soot and/or dust. That is a factor of three times or more radiative absorption from getting dirty. I fine layer that diminishes the albedo to 0.7 is invisible except under a microscope or other equipment measuring reflectivity.

How about these:

For just 10 ppb on the surface:


We find evidence that black soot aerosols deposited on Tibetan glaciers have been a significant contributing factor to observed rapid glacier retreat. Reduced black soot emissions, in addition to reduced greenhouse gases, may be required to avoid demise of Himalayan glaciers and retain the benefits of glaciers for seasonal fresh water supplies.
​


BC concentrations of 10 ng g−1 significantly alter the albedo (reflectivity) of a thick snow layer. The visible albedo of deep fresh snow, about 0.9–0.97, is decreased by 0.01–0.04 by a BC amount of 10 ng g−1 (16, 18), thus increasing absorption (1 minus albedo) of visible radiation by 10–100%, depending on the size and shape of snow crystals and on whether the soot is incorporated within snow crystals or externally mixed
​


The impact of albedo change is magnified in the spring, at the start of the melt season, because it allows melt to begin earlier. Then, as melting snow tends to retain some aerosols, the surface concentration of black soot increases, and BC becomes even more effective at increasing melt of snow and ice.
​

Black soot and the survival of Tibetan glaciers


BC has been implicated in previous studies as
potentially disrupting Arctic climate. Clarke and Noone
[1985] found that snow albedos are reduced by 1–3% in
fresh snow and by another factor of 3 as the snow ages and
the BC becomes more concentrated.
​

Distant origins of Arctic black carbon: A Goddard Institute for Space Studies ModelE experiment
This is probably another reason we see a net ice loss in Antarctica and Greenland, but in the arctic:


BC deposition in Greenland is about 10 times greater than in Antarctica and 10 times less than in Tibet.
​


In addition to absorbing radiation when lofted in the
atmosphere, BC also causes surface warming when deposited
on snow and ice surfaces [Flanner et al., 2007; Hansen and
Nazarenko, 2004]. Sensitive regions (e.g., the Arctic and
the Himalayas) are particularly vulnerable to warming due
to the snow albedo effect [Kopacz et al., 2011; McConnell,
2010], which tends to enhance snow and ice melting due to
the absorption caused by the increased BC deposition.
​

Historical and future black carbon deposition on the three ice caps: Ice core measurements and model simulations from 1850 to 2100

I have seen more dramatic numbers than these in other studies, but don't recall the keywords I need to find the studies.

Whether from the sun, or forcing from greenhouse gasses, the snow is warming twice as fast or more from the albedo changes cause by soot.
Click to expand...

Do you have any figures for the actual amount of heat energy being absorbed by snow/ice/dirt for Greenland ice? The Watts per square meter numbers?
 
Tim the plumber said:
Do you have any figures for the actual amount of heat energy being absorbed by snow/ice/dirt for Greenland ice? The Watts per square meter numbers?
Click to expand...

Some papers express the number in equivalent forcing, which isn't the same, and global rather than regional. Any of this is calculated from models which may be incorrect, and no better than greenhouse gas calculations. The papers referring to such things started some time back. I'm not going to keep looking for papers I started reading so many years ago. The simple fact is that absorption is 1 - albedo. If the albedo starts at 0.95, and decreases to 0.9. The absorption is doubled. These changes, outside of high latitude volcanic eruption, are primarily soot induced. Soot will absorb nearly the entire EM spectra, so the changes affect from solar UV to longwave.

Consider a 100%+ of EM absorption by soot vs. less than a 10% increase of warming due greenhouse gas changes. I get the less than 10% by assuming that CO2 forcing increased by 2/32, or 6.25%of the total CO2 forcing. It should be apparent that soot is melting the ice at a far quicker rate than greenhouse gas changes, since that calculation has CO2 at a 6.25% warming increase. Keep in mind, a doubling of CO2 increase the forcing of CO2 by only 3.71/32, or 11.6%. However, albedo changes are a linear response instead of logarithmic.

The increases of the algae on ice also change the albedo of ice.

At our level of the constant burning fossil fuels, the aerosols in the atmosphere remain rather permanently, unlike periodic volcano eruptions.
 
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Lord of Planar said:
Some papers express the number in equivalent forcing, which isn't the same, and global rather than regional. Any of this is calculated from models which may be incorrect, and no better than greenhouse gas calculations. The papers referring to such things started some time back. I'm not going to keep looking for papers I started reading so many years ago. The simple fact is that absorption is 1 - albedo. If the albedo starts at 0.95, and decreases to 0.9. The absorption is doubled. These changes, outside of high latitude volcanic eruption, are primarily soot induced. Soot will absorb nearly the entire EM spectra, so the changes affect from solar UV to longwave.

Consider a 100%+ of EM absorption by soot vs. less than a 10% increase of warming due greenhouse gas changes. I get the less than 10% by assuming that CO2 forcing increased by 2/32, or 6.25%of the total CO2 forcing. It should be apparent that soot is melting the ice at a far quicker rate than greenhouse gas changes, since that calculation has CO2 at a 6.25% warming increase. Keep in mind, a doubling of CO2 increase the forcing of CO2 by only 3.71/32, or 11.6%. However, albedo changes are a linear response instead of logarithmic.

The increases of the algae on ice also change the albedo of ice.

At our level of the constant burning fossil fuels, the aerosols in the atmosphere remain rather permanently, unlike periodic volcano eruptions.
Click to expand...

Wonder how you read so many papers years ago when you told us you subscribe to one (1) journal, and that was a year or two ago, if I recall.

Enquiring minds want to know!
 
Lord of Planar said:
Some papers express the number in equivalent forcing, which isn't the same, and global rather than regional. Any of this is calculated from models which may be incorrect, and no better than greenhouse gas calculations. The papers referring to such things started some time back. I'm not going to keep looking for papers I started reading so many years ago. The simple fact is that absorption is 1 - albedo. If the albedo starts at 0.95, and decreases to 0.9. The absorption is doubled. These changes, outside of high latitude volcanic eruption, are primarily soot induced. Soot will absorb nearly the entire EM spectra, so the changes affect from solar UV to longwave.

Consider a 100%+ of EM absorption by soot vs. less than a 10% increase of warming due greenhouse gas changes. I get the less than 10% by assuming that CO2 forcing increased by 2/32, or 6.25%of the total CO2 forcing. It should be apparent that soot is melting the ice at a far quicker rate than greenhouse gas changes, since that calculation has CO2 at a 6.25% warming increase. Keep in mind, a doubling of CO2 increase the forcing of CO2 by only 3.71/32, or 11.6%. However, albedo changes are a linear response instead of logarithmic.

The increases of the algae on ice also change the albedo of ice.

At our level of the constant burning fossil fuels, the aerosols in the atmosphere remain rather permanently, unlike periodic volcano eruptions.
Click to expand...

The reason I am after this is to do the simple sum of working out just how much snow and ice could possibly melt on Greenland's ice sheet.

So I need the total insolation, the angle of the sun, the albedo, the initial temperature of the surface or something close to it and thus the maximum melt rate from the top pops out. If it's less than 1m of melting (w.e.) then there has to be a net build up of ice. Well, there is a little bit of melting from geothermal energy and a little bit of flow down the exit glaciers but....
 
Tim the plumber said:

The reason I am after this is to do the simple sum of working out just how much snow and ice could possibly melt on Greenland's ice sheet.

So I need the total insolation, the angle of the sun, the albedo, the initial temperature of the surface or something close to it and thus the maximum melt rate from the top pops out. If it's less than 1m of melting (w.e.) then there has to be a net build up of ice. Well, there is a little bit of melting from geothermal energy and a little bit of flow down the exit glaciers but....
Click to expand...

Well, I don't care about the absolutes. To me, it is common sense that the change in albedo has a substantial impact on ice warming vs. the minor changes in greenhouse gas forcing.

All the forcing on a global scale is getting close to 400 W/m^2. The AR5 say we have increased the forcing by what? About 2 W/m^2? This is 1/2%, when depending on where you look, soot has increase the absorption of this radiate heat by 25% or more, and in some places by more than 200%. Now the forcing at the northern ice isn't going to be the 400 W/m^2, but it doesn't matter when you look at the percentage changes.

Point is, greenhouse gas changes are minuscule for melting ice vs. albedo changes.

Yes... The geothermal changes that melt the ice where the land meets an ice sheet. This is also a factor that has changes outweighing greenhouse forcing changes.
 
Lord of Planar said:
Well, I don't care about the absolutes. To me, it is common sense that the change in albedo has a substantial impact on ice warming vs. the minor changes in greenhouse gas forcing.

All the forcing on a global scale is getting close to 400 W/m^2. The AR5 say we have increased the forcing by what? About 2 W/m^2? This is 1/2%, when depending on where you look, soot has increase the absorption of this radiate heat by 25% or more, and in some places by more than 200%. Now the forcing at the northern ice isn't going to be the 400 W/m^2, but it doesn't matter when you look at the percentage changes.

Point is, greenhouse gas changes are minuscule for melting ice vs. albedo changes.

Yes... The geothermal changes that melt the ice where the land meets an ice sheet. This is also a factor that has changes outweighing greenhouse forcing changes.
Click to expand...

Yes. But if the increase in melting is of 5cm to 15cm who cares given the 1m snow fall?
 
Tim the plumber said:
Yes. But if the increase in melting is of 5cm to 15cm who cares given the 1m snow fall?
Click to expand...

It matters as the ice sheets flow.

Think of them as rivers, but moving inches a year instead of feet per second.

Consider early melt ice as no longer being part of that solid river, with the same end results as diminishing the net snowfall, reducing the volume at the end.
 
Lord of Planar said:
It matters as the ice sheets flow.

Think of them as rivers, but moving inches a year instead of feet per second.

Consider early melt ice as no longer being part of that solid river, with the same end results as diminishing the net snowfall, reducing the volume at the end.
Click to expand...

Consider that the inches per year flow rate of the glacier is determined by the gradient of the land it is flowing down and the thickness of the ice at the start of the flow.

This will increase as the thickness of that inital ice increases but given the the increase is tiny comapred to the total the flow rate will not be significantly different.

So appart from the terminal edge of the ice moving inwards due to increased temperatures there is very little difference in mass.

The figure for the energy absorption of the ice sheet is thus important because it will allow the maximum possible melt rate to be found. If it significantly less than the snow fall rate then Greenland is increasing in ice mass.
 
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