Global warming and the Ice Caps
Ron writes:
Well, I will read it, though I don't have time right now. But from the quotes he gave, I've got a couple off-the-cuff thoughts:
This confuses me, because I would've expected the polar ice caps to have been roughly equal, yet this states that Antarcitica is the vaast majority of it, and the rest of the glaciers of Eareth, including the Arctic polar region and all other (moutainous) glaciers are only 2m SQ Km. Or perhaps the article is mistaken.
So anyway, take a generous estimate, and say that a bit more than 10% of the Earth is covered by polar and other glacier ice. That's an overestimate, but that's okay, because the seriousness of global warming justifies a worst-case scenario calculation. (As long as the assumptions are acknowledged).
This View of Earth shows us that average albedo is .37. Figure that this includes the relatively high albedo of the ice caps whiuch we've postulaated are disappearing. This would make the average albedo lower, but since 90% of the Earth is NOT covered in ice currently, we're talking about 10% area at 90% albedo changing to some value slightly higher than 37% albedo. Completely discounting the increase in albedo that extra cloud cover would make (because all that H20 is not going to be water, a significant amount will be water vapor), which increase in cloud cover would be significant (see: Nuclear Winter).
Another factor: Out of this 10 or 15% of the Earth's surface which is covered in persistant ice, how much is polar? 56% of glacier surface is Subpolar: That means that the area with the greatest change in albedo is also the area that recieves the least amount of sunlight (as we all know, the latitudes closest to the poles recieve the leat amount of sunlight, both in absolute time and in absolute intensity, because A: the angle puts the poles mostly in shadow for half the year, and B: the increased angle 'of attack' for sunlight means that a greater mass of atmosphere lies between incoming sunlight and the surface, which attenuates the amount of energy which is actually obvserved at surface level. Additionally, the oblique angle ensures that some light waves are refracted to never reach the surface.
Age-old question: Why is the sky blue? Answer: Because longer wavelength red light does not refract as much, while shorter wavelength blue-ish light is refracted and scattered toward the surface during the day. At dawn and dusk, the red-ish light is at an angle where is mostly coming straight in, and thus dawn and dusk are redder.
At the poles, a similar condition obtains to dawn and dusk, where the longer wavelength (less energetic) visible light is the majority that reaches the surface. Bottom line, the poles receive MUCH less energy from the sun than the equator. That's why it's colder there, and that's why even if enough warming happened to melt the caps, which is unlikely in the extreme due to feedback mechanisms in the atmosphere, and which none but the most chicken-little-like alarmist even mention, the increased albedo of the polar regions, which would come down from about 90% to something like the average of the rest of the planet (37%), and would receive a fraction of the solar energy that the lower latitudes receive, would not have an overwhelming effect on warming the planet.
In fact, the most significant place to measure global warming, would seem to not be the poles, but rather the equator. If tempreatures at the equator start drastically rising, I would see that as being a very alarming sign of the 'cliff' phenomena in global warming.
This is a very, very long read. Yet I highly recommend it.
Normally, I don't pay TOO much attention to the Guardian, but this is a very, very thought-provoking issue.
It's quite a long read, I recommend the articles "oil and troubled water" and The Drowned World:
Well, I will read it, though I don't have time right now. But from the quotes he gave, I've got a couple off-the-cuff thoughts:
albedo:Glossary of Glacial Terms
The percent reflectivity of a surface. Ice may reflect up to 90 percent of incoming solar radiation (albedo = 90).
At the present, glacier ice covers about 15 million sq km (5.8 million sq mi), or 10 percent, of Earth’s land area. [...] The ice sheet in Antarctica covers 13 million sq km (5 million sq mi).Encarta
This confuses me, because I would've expected the polar ice caps to have been roughly equal, yet this states that Antarcitica is the vaast majority of it, and the rest of the glaciers of Eareth, including the Arctic polar region and all other (moutainous) glaciers are only 2m SQ Km. Or perhaps the article is mistaken.
So anyway, take a generous estimate, and say that a bit more than 10% of the Earth is covered by polar and other glacier ice. That's an overestimate, but that's okay, because the seriousness of global warming justifies a worst-case scenario calculation. (As long as the assumptions are acknowledged).
This View of Earth shows us that average albedo is .37. Figure that this includes the relatively high albedo of the ice caps whiuch we've postulaated are disappearing. This would make the average albedo lower, but since 90% of the Earth is NOT covered in ice currently, we're talking about 10% area at 90% albedo changing to some value slightly higher than 37% albedo. Completely discounting the increase in albedo that extra cloud cover would make (because all that H20 is not going to be water, a significant amount will be water vapor), which increase in cloud cover would be significant (see: Nuclear Winter).
Another factor: Out of this 10 or 15% of the Earth's surface which is covered in persistant ice, how much is polar? 56% of glacier surface is Subpolar: That means that the area with the greatest change in albedo is also the area that recieves the least amount of sunlight (as we all know, the latitudes closest to the poles recieve the leat amount of sunlight, both in absolute time and in absolute intensity, because A: the angle puts the poles mostly in shadow for half the year, and B: the increased angle 'of attack' for sunlight means that a greater mass of atmosphere lies between incoming sunlight and the surface, which attenuates the amount of energy which is actually obvserved at surface level. Additionally, the oblique angle ensures that some light waves are refracted to never reach the surface.
Age-old question: Why is the sky blue? Answer: Because longer wavelength red light does not refract as much, while shorter wavelength blue-ish light is refracted and scattered toward the surface during the day. At dawn and dusk, the red-ish light is at an angle where is mostly coming straight in, and thus dawn and dusk are redder.
At the poles, a similar condition obtains to dawn and dusk, where the longer wavelength (less energetic) visible light is the majority that reaches the surface. Bottom line, the poles receive MUCH less energy from the sun than the equator. That's why it's colder there, and that's why even if enough warming happened to melt the caps, which is unlikely in the extreme due to feedback mechanisms in the atmosphere, and which none but the most chicken-little-like alarmist even mention, the increased albedo of the polar regions, which would come down from about 90% to something like the average of the rest of the planet (37%), and would receive a fraction of the solar energy that the lower latitudes receive, would not have an overwhelming effect on warming the planet.
In fact, the most significant place to measure global warming, would seem to not be the poles, but rather the equator. If tempreatures at the equator start drastically rising, I would see that as being a very alarming sign of the 'cliff' phenomena in global warming.
posted by Larry at
9/11/2004 04:52:00 AM
5 Comments:
Adam again, dude.
Couple of points:
Uh the article points to increased world tempurature (from the global mechanism of CO2) producing generally higher tempuratures.
This is a general and global thing.
This melts more ice, i'd guess as a general assumption. (i'm not being facicious, that might actaully be a wrong assumption.)
Once the ice has started to melt, the SPOT albedo of the ice is reduced. That is localised thermodynamic properties of the area are changed, due to the colour change, from white ice to dark whatever.
This means the area (being coloured darker) now absorbs more heat, melting yet more ice. lets say these areas go to rock (0.3) from snow (0.6) thats twice as much heat going into those areas and melting or stoping the forming of ice / snow.
I'm unsure of which type of Albedo you are quoting, so i've used the numbers from here: http://scienceworld.wolfram.com/physics/Albedo.html
As a totally seperate issue, the globe keeps getting hotter, from the CO2 and also possibly from all that extra water vapour released (you keep telling me is a greenhouse gas). The overall albedo of the planet, probably stays the same for the reasons you've stated. It's not the cause of the initial global warming. and sea levels continue to rise.
Is all that clear? from your post it seems like either you've really missunderstood this or your trying to obscure the issue, for what ever reason.
"Uh the article points to increased world tempurature (from the global mechanism of CO2)"
Which has yet to be proven, it's still speculation and theory. Hotly contested theory, in fact, and not just among pundits, politicians, and ignorant hicks.
"Once the ice has started to melt, the SPOT albedo of the ice is reduced. That is localised thermodynamic properties of the area are changed, due to the colour change, from white ice to dark whatever.
This means the area (being coloured darker) now absorbs more heat, melting yet more ice. lets say these areas go to rock (0.3) from snow (0.6) thats twice as much heat going into those areas and melting or stoping the forming of ice / snow. "
Right. But let's examine one assumption: what the albedo of the unvcovered area will be. It's likely to be pretty close to the average of the rest of the world, right? I addressed that in my post. You're also ignoring (as I addressed in my post) that the majority of the Earth's ice cover is at the poles, where even if it were completely uncovered, and the uncovered area consisted of macadam blacktop, it would STILL garner less heat than lower latitudes, purely because of the angle of incidence of sunlight striking that portion of the planet.
"As a totally seperate issue, the globe keeps getting hotter, from the CO2 and also possibly from all that extra water vapour released (you keep telling me is a greenhouse gas). The overall albedo of the planet, probably stays the same for the reasons you've stated. It's not the cause of the initial global warming. and sea levels continue to rise."
Okay, so I think you have a misunderstanding here: Greenhouse gases decrease the albedo of the planet. Not just making it 'darker' to the eye, but trapping infrared and ultraviolet also, increasing the solar energy and as it becomes trapped, converting it to heat. My point about compensating factors are such that cloud cover will reflect certain wavelengths, much like the postulated 'nuclear winter' would throw dust particles in the air. None of this is proven beyond a shadow of a doubt, but it's good theory. On a cloudy day, less sunlight hits the surface right? It's cooler then. Adding to complexity, this heat may just be getting trapped in air ata higher altitude, but I think it's pretty acceptable to say that increased cloud cover (as distinct from water vapor, as cloud cover is realy condensed water that it still scattered and in small enough droplets to stay aloft) will decrease the albedo of the Earthe significantly. So if we get enough ice melting to increase the cloud cover, then we could actually see the tmepreature drop.
Now all this doomsday speculation doesn't take into account thatt this is an on-going process, and one factor feeds back into other processes, producing rough equilibrium. Again, I believ it is possible that this euqilibrium could shift, for natural or anthropogenic reasons, but I don't believe the mechanisms are well-enough understand to base policy on yet. Especially a policy which will have far-reaching (catastrophic?) economic impact, like Kyoto. I can't even be sure if it's going to rain or not any given day, no matter how many weather reports I watch.
"Is all that clear? from your post it seems like either you've really missunderstood this or your trying to obscure the issue, for what ever reason."
You should know me better. Obscuring the issue? I know it's possible I'm misunderstaning something- I'm a layman working with conflicting information presented to me by various 'experts', many of whom honestly compromise their credibility with outrageous claims and doomsday warnings that don't come true. Paul Ehrlich, for example.
If this keeps up i'm going to have to get an account. (adam again.)
I'm gonna break this down for you as simply as possible.
Okay, yes CO2 heating of the atmosphere is a theory. That's not what we're talking about here.
Lets make the assumption, that the globe is getting hotter. We have to make this assumption, because if we don't then the Ice caps stay steady state and this is a pointless discussion. There is evidence that they are changing, but we are not talking about that evidence.
Now, Albedo. There are several different types of albedo, as i pointed out in that link in my above comment.
The overall Albedo of the planet, is in this case irrelevent ( and has a different meaning, the .37 figure is the astrolonomical Albedo and has to do with more than just IR radiation). we're not concerned with that. were disscussing how the ice caps melt, and how it occurs quicker because of the colour change of ground exposed. It is pretty unlikely that this alone would effect the planetary albedo, and again largley irrelevent to ocean level rise issue.
So are you following this: Black ice melts quicker than white ice. That's what Albedo means.
The more ground that gets exposed, the faster the patch will grow, since it can absorbe twice as much enegy. Remembering that this energy will have to be removed, by forming ice. Now i've used the figures for incident energy, which show a doubling of the absorbsion. Those figures come from that link, and may be wrong, but the basic generality that black things get hotter than white things isn't. It's high school physics.
Now, you say the albedo of the exposed areas goes to the average of the rest of the world. sure, let say it does. It doesn't matter, because the ice has melted, and the sea level has risen. remember that this is in the context of a warmer globe, not due to the ice melting, but ofr other reasons.
Now, also you state that these polar areas recieve less heat from the sun generally. Sure that's true. But lets assume that the amount of sunlight hitting the surface there stays relativly constant. The ice / rock is now absorbing more heat energy from those same rays, than the plain ice was before. so it doesn't matter, how much sunlight there is, cause they are now using it twice as well(by the ice to rock figure).
The misunderstanding you have is this, that the albedo of the planet is involved. it isn't, this is all about the albedo of a couple of isolated areas that contain a shirt load of water!.
Oh, and as for increased cloud cover, droping the tempurature.... well, venus our best example of a run away greenhouse effect, has plenty of clouds. Still, i'm more than alittle concerned about the sea level rising by that metre....
So forget planetary albedo, it's irrelevent.
I hope i've not ranted on about this to much.
We haven't discussed the theory of global warming here, or it's varacity.
You guys need to add another factor in this: geologic time. Can we honestly make any theories at that level without more than 100 years' accurate data?
Adam again.
Acurate data going back millions of years is found in the deep core ice samples taken in polar regions. it's also avalible from sediment deposits.
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