No mention of missing “M’s” here in this press release from University of Melbourne
Melting sea ice has been shown to be a major cause of warming in the Arctic according to a University of Melbourne study.
Findings published in Nature today reveal the rapid melting of sea ice has dramatically increased the levels of warming in the region in the last two decades.
Lead author Dr James Screen of the School of Earth Sciences at the University of Melbourne says the increased Arctic warming was due to a positive feedback between sea ice melting and atmospheric warming.
“The sea ice acts like a shiny lid on the Arctic Ocean. When it is heated, it reflects most of the incoming sunlight back into space. When the sea ice melts, more heat is absorbed by the water. The warmer water then heats the atmosphere above it.”
“What we found is this feedback system has warmed the atmosphere at a faster rate than it would otherwise,” he says.
Using the latest observational data from the European Centre for Medium-Range Weather Forecasting, Dr Screen was able to uncover a distinctive pattern of warming, highly consistent with the loss of sea ice.
“In the study, we investigated at what level in the atmosphere the warming was occurring. What stood out was how highly concentrated the warming was in the lower atmosphere than anywhere else. I was then able to make the link between the warming pattern and the melting of the sea ice.”
The findings question previous thought that warmer air transported from lower latitudes toward the pole, or changes in cloud cover, are the primary causes of enhanced Arctic warming.
Dr Screen says prior to this latest data set being available there was a lot of contrasting information and inconclusive data.
“This current data has provided a fuller picture of what is happening in the region,” he says.
Over the past 20 years the Arctic has experienced the fastest warming of any region on the planet. Researchers around the globe have been trying to find out why.
Researchers say warming has been partly caused by increasing human greenhouse gas emissions. At the same time, the Arctic sea ice has been declining dramatically. In summer 2007 the Arctic had the lowest sea ice cover on record. Since then levels have recovered a little but the long-term trend is still one of decreasing ice.
Professor Ian Simmonds, of the University’s School of Earth Sciences and coauthor on the paper says the findings are significant.
“It was previously thought that loss of sea ice could cause further warming. Now we have confirmation this is already happening.”
kadaka (KD Knoebel) says:
May 1, 2010 at 9:40 am
From skye on May 1, 2010 at 8:27 am:
(…) (http://rapidfire.sci.gsfc.nasa.gov/subsets/?mosaic=Arctic.2010121.terra.4km).
(…)
But again, I will let the visible satellite imagery speak for itself. If water had the same reflectance as ice, you wouldn’t be able to see the difference between the two in the imagery. But, you do.
Such wonderful imagery looking straight down!
Now post some pics showing what it looks like at the small angles, let us see what the reflectance looks like as incoming light from the Sun would actually “see” it.
What the MODIS is showing is reflected sunlight!
Phil. says: May 1, 2010 at 11:26 am
What the MODIS is showing is reflected sunlight!
Modis is showing reflected sunlight that reaches the satellite overhead – mainly that will be sunlight reflected off irregular surfaces such as ice crystals. It is not showing sunlight reflected off surface water which will leave the surface at the 10 or 20 degree opposite angle to that which the sunlight is received .
http://www.shunya.net/Pictures/NorthPole/Yamal-reflection.jpg
http://twistedsifter.com/wp-content/uploads/2009/04/north-pole-sunset.jpg
http://www.jodcast.net/archive/200802Extra/iss_view.jpg
kadaka (KD Knoebel) says:
May 1, 2010 at 9:40 am
The sun angles are still rather low right now in the Arctic especially at the most northern latitudes. But go ahead and look at September imagery and you will see the same thing (dark=water, bright=ice or clouds).
And so that you understand, MODIS is measuring the reflected solar energy. And it scans up to angles as oblique as +/- 55 degrees. I’m not sure what you mean by “incoming light from the Sun would actually see it”.
Snow and ice do not reflect the incoming solar radiation equally in all directions. In the forward direction (i.e. if your sensor is in the same position as the sun), snow is very forward scattering (i.e. you are receiving more energy in that direction than if you were opposite the sun). You can google snow BRDF and water BRDF to see for yourself the distribution of reflectance at different angles and how viewing the surface in the forward or backward direction and at nadir or oblique viewing angles looks like. You will notice that both water and snow show strong forward scattering, so you can still discriminate between the two.
Also, the albedo is the integral of the albedo over all angles.
Bill, what you are seeing in this link: http://rapidfire.sci.gsfc.nasa.gov/subsets/?subset=Arctic_r04c03.2009253.terra.2km
is new ice formation (very thin ice) at the edges of the consolidated ice pack, and a lot of cloud cover not just over the consolidated ice pack, but also over the open water areas. If you zoom into the 250 m version you can see this more easily for yourself. But of course you do still notice where the cracks (leads) in the ice are and the ice edge by the differences in color (i.e. albedo) between ice and open water.
MODIS data is so useful for looking at the ice cover, it’s too bad it’s cloudy most of the time in the Arctic.
TomRude, Reur April 29, 2010 at 9:48 pm
Thanks for your:
That link is worth repeating again!
BTW, I’m thinking of changing my ID to “Embarrassed of Melbourne’
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Bill Illis, Icarus, Skye, Phil, et al: Did you see that link above?
At a quick first look I did a search for the word albedo, and found a handful of hits in the text, but guess what: no mention of any values, probably because it is a very complicated topic, that is fraught with naïve contradictions or ambiguity in some of the literature.
To check-out what Bill has been saying about water reflection when the sun is low in the sky, look out over open water whilst the sun is setting towards the normal horizon on a clear day. (this cannot be seen from a satellite). As for the claim that snow and ice albedo changes similarly, well, that is even more complicated depending on grain size and age etc. And anyway, any increase from a nominally high normal (90 degree vertical) value has less significance. It is probably less confusing to talk of reflection and incident angles of light.
I’m not totally sure about this, but I believe the very real optical difference with water is in its surface tension layer.
Anyhow, see my next post which will show graphically that the solar energy input does NOT correlate with the seasonal regimes of freezing and melting. (which in turn means that albedo arguments are not significant in effect)
From skye on May 1, 2010 at 1:25 pm:
The sun angles are still rather low right now in the Arctic especially at the most northern latitudes. But go ahead and look at September imagery and you will see the same thing (dark=water, bright=ice or clouds).
And so that you understand, MODIS is measuring the reflected solar energy. And it scans up to angles as oblique as +/- 55 degrees. I’m not sure what you mean by “incoming light from the Sun would actually see it”.
Thus I wonder if you are being deliberately obtuse. You realize the “sun angles” are low (small), yet you do not realize I am talking about those angles? Granted it may be hard to tell if all one reads is your horribly mis-selected partial quote, but still…
MODIS can scan up to 55deg from vertical. So what? The sunlight comes in at very low angles. At small angles from horizontal the sunlight will reflect, not be absorbed. As I previously mentioned, a certain amount of the sunlight will get blocked from hitting the water by the ice itself. Thus going by MODIS pics yields a false image of what happens to the incoming light as by those small angles there will be a lot less open water “visible” to the incoming light thus less energy absorbed than what one would infer from the MODIS view.
Is that really so hard for you to comprehend?
Bill Illis, Icarus, Skye, Phil, et al: Did you see that link above?
and Kadaka.
The points about the albedo feedback affect seem to be missing from these posts. The issue is that during summer the ocean absorbs solar energy from the sun and this is released back to the atmosphere during autumn with the sun dips below the horizon again and air temperatures fall. There is no way the ocean can refreeze w/out the ocean first releasing that heat back to the atmosphere. The ice-albedo affect comes into play as the ocean loses it’s highly reflective sea ice cover during summer, thereby allowing the ocean to absorb more of this energy during the summer. The argument about September low sun angles is completely mute.
But Kadaka, both snow/ice and water show strong forward scattering at low sun angles (or high solar zenith angles however you want to define it), and this is even stronger at low sensor viewing angles (or high sensor zenith angles). All satellite visible instruments observe the surface at 1 combination of viewing/solar angles. But in the Arctic there are many of these observations per day, thereby allowing some characterization of the surface BRDF to be achieved. This is what the MOD43 (MODIS albedo and BRDF data product) achieve on an 8-day time interval.
Kadaka, if you don’t want to believe in the ice-albedo feedback that Skye has tried to explain to you, there are several recent journal articles that discuss this in depth. Papers by Perovich do a good job explaining this in relatively easy to understand language. You can also plot anomalies and trends in total absorbed solar radiation from NCEP, JRA-25 or ERA-40 Interim analysis and see for yourself how the amount of solar radiation absorbed in the Arctic has been changing as the sea ice has been declining during summer.
Bill Illis, Icarus, Skye, et al:
There is a discussion on the low levels of arctic solar energy and albedo on a recent thread starting here. It utilizes much information, even webcams, available at Longyearbyen in the Norwegian Svalbard archipelago. The location is at 78:13 north and it is seemingly right on the typical sea-ice boundary. This particular Longyearbyen website enables selection of many parameters daily/monthly, and has enabled me to construct this graph, showing the midday sun elevation versus sea-ice cover. The inference is that the low solar energy and the albedo considerations do not adequately correlate with the sea-ice cycle, and that therefore there must be other far more powerful causations.
Or, in other words, the popular albedo feedback alarmism is grossly exaggerated.
kadaka (KD Knoebel) says:
May 2, 2010 at 2:14 pm
MODIS can scan up to 55deg from vertical. So what? The sunlight comes in at very low angles. At small angles from horizontal the sunlight will reflect, not be absorbed.
The reflected light will be the horizontally polarized light, vertically polarized light will be absorbed.
Bob_FJ says:
May 2, 2010 at 3:52 pm
Bill Illis, Icarus, Skye, et al:
There is a discussion on the low levels of arctic solar energy and albedo on a recent thread starting here. It utilizes much information, even webcams, available at Longyearbyen in the Norwegian Svalbard archipelago. The location is at 78:13 north and it is seemingly right on the typical sea-ice boundary. This particular Longyearbyen website enables selection of many parameters daily/monthly, and has enabled me to construct this graph, showing the midday sun elevation versus sea-ice cover. The inference is that the low solar energy and the albedo considerations do not adequately correlate with the sea-ice cycle, and that therefore there must be other far more powerful causations.
Or, in other words, the popular albedo feedback alarmism is grossly exaggerated.
It might be more illuminating to plot vs rate of change of sea cover!
Wildred wrote in part May 2, 2010 at 2:54 pm
Wildred, further to my May 2, 2010 at 3:52 pm which crossed yours:
It is a matter of scale that you need to consider; YES, there is arguably an albedo feedback but it is evidently small compared with many other processes. A fundamental thing that you seem to overlook is that the nominal solar energy per unit area is greatly reduced in the region where sea-ice prevails. (nominally zero at the “solar poles“). Also, its path length through the atmosphere is greatly increased. (although there is some scattering) Another fundamental oversight is that you seem to imply that the sun is the primary heating source in the region. However more importantly heat is transferred from lower latitudes via various air and sea circulations, and, erratically via various oceanic oscillation highs.
There has been mention that the newly exposed ocean, (a fraction of the winter ice area), absorbs solar energy all summer, and that this is then only released to the atmosphere in autumn. (when thermo’ law 2 then permits that). Well for a start, the “early heat”, when comes autumn, is no longer in the region or at the ocean surface , because of ocean dynamics.
I’ve highlighted some text in yellow in the composite graph that I showed earlier. Wildred, please study that text, and if there is anything you disagree with, or don’t understand, please let me know.
Incidentally, sea-ice as usually defined may have significant areas of exposed water. (up to 85%?). So how does that albedo thing work again?
And, don’t forget wind-packing variations, and wind-drift into warmer waters. And……. And submarines in open water at/near the poles, out of relevant satellite sight.
I’ve built a global Albedo model for another project and actually crunched through the numbers awhile ago. While sea ice melt in the high Arctic may have local impacts, the overall area is such a small component of the total Earth surface area and it receives such a small percentage of the total Earth solar radiation budget, that ice melting early in the season or late in the season has very, very little impact on global temperatures.
It is not until sea ice, snow and glaciers become permanent throughout the summer at lower latitudes, 70N and lower, that the feedback cycle starts to become important enough to take note of. I guess that has to start with permanent sea ice in the Arctic ocean first, but it makes little difference when there is a seasonal melt cycle as occurs nows.
If the sea ice melted out completely 2 months earlier than it semi-melts now (and followed the seasonal pattern of declining Albedo 2 months earlier) , the global Albedo would only decline from 0.2982 to 0.2973 and global temperature would increase by 0.09C.
Phil. said on May 2, 2010 at 5:03 pm:
The reflected light will be the horizontally polarized light, vertically polarized light will be absorbed.
Only fully true at Brewster’s angle, which is about 53 deg from the normal (from vertical) air to water. At greater angles, as would be seen in the Arctic, the reflection coefficient for the vertically polarized light rises quickly to total reflection (per the Fresnel equations) Yes, the vertically polarized light will also be reflected, by differing amounts on both sides of Brewster’s angle.
“”” kadaka (KD Knoebel) says:
May 3, 2010 at 9:53 am
Phil. said on May 2, 2010 at 5:03 pm:
The reflected light will be the horizontally polarized light, vertically polarized light will be absorbed.
Only fully true at Brewster’s angle, which is about 53 deg from the normal (from vertical) air to water. At greater angles, as would be seen in the Arctic, the reflection coefficient for the vertically polarized light rises quickly to total reflection (per the Fresnel equations) Yes, the vertically polarized light will also be reflected, by differing amounts on both sides of Brewster’s angle. “””
Well I’m pretty sure that Phil knows alla bout fresnel Reflection and polarisation of light. My only quibble with his statement:- “”” The reflected light will be the horizontally polarized light, vertically polarized light will be absorbed. “”” would be that it would be more correct to say that the vertically polarised light is TRANSMITTED rather than ABSORBED; but I’m also sure that Phil meant “aborbed by the ocean” and after transmission that too is a pretty safe bet.
I would also prefer to put it slightly differently; in that the “vertical polarisation” is almost certainly not vertical since it must be perpendicular to the ray direction; so I would say that polarisation in the plane of incidence is transmitted (and then absorbed) while the polarisation perpendicular to the plane of incidence it reflected. And of course that is for the Electric Vector, and once again true only for the Brewster angle or at least near that.
As a practical matter, at the Brewster angle, the reflection coefficient for the perpendicular polarisation component is about double what it is at normal incidence; so the loss of the transmitted component, is almost made up by the enhanced reflectance of the perpendicular polarisation.
And finally; I’ll be gobsmacked if all of that is not perfectly well known to Phil.
One can’t write a PhD thesis on every little thing that comes up.
And to close the loop on the above; for incidence on water at the Brewster angle the reflection coefficient of the polarisation perpendicular to the plane of incidence; is about 4-5%; so the rest of that polarisation is also transmitted into the water, and subsequently absorbed.
So at the Brewster angle the reflected light is indeed plane polarised; but the transmitted light is only elliptically polarised; and quite weakly at that.
Phil, you wrote May 2, 2010 at 7:31 pm
I don’t think it would be worth the effort.
The important thing is that the existing plot shows that whilst solar input in the spring correlates expectantly with reducing sea-ice; in the Autumn, it does not. That is to say that counter-intuitively, from about mid August, (depending on year), sea-ice levels start levelling-off and then rise, despite being exposed to a somewhat similar level of solar input to that of spring. (which seemingly results in the opposite effect of melting). Oh, and Autumn is the time when the ocean releases the “summer-stored-heat” back to the atmosphere right?
Anyhow, if you want to get an idea of rate of change of sea cover, then it can be visualized in a unit-less way in the varying slope steepness.