Total snow cover for the northern hemisphere (NH) is an important indicator of the condition of the climate, and a factor affecting northern-hemisphere albedo. More snow cover doesn’t necessarily indicate colder temperatures. Total snowfall depends on temperature and humidity, and warmer temperatures increase the amount of water vapor the air can hold, increasing the total potential snowfall. Still, they’re at least partly related to temperature; there’s certainly more snow during winter than summer. Snow is an important part of the earth’s albedo, or reflectivity to incoming sunlight; fresh snow is one of the most highly reflective surfaces found on the planet.
Has snow cover shown trends over the last several decades? NH snow cover data since late 1966 can be obtained from Rutgers University. Let’s take a look.
A plot of snow cover in the NH shows a distinct (and not unexpected) strong annual pattern, more in winter and less in summer:
The annual pattern is easier to see if we zoom in on just a few years of data:
To look for trends, it’s useful to remove the annual cycle from the data in order to compute the difference between a given month’s snow cover and what’s typical for that month; this defines snow cover anomaly:
There’s a clear, and statistically significant, trend over the last 40 years. Annual average NH snow cover has declined by about 41,000 km^2 per year.
But the trend has not in fact been linear. We can smooth the snow cover data with a Savitsky-Golay filter, which not only enables us to compute the estimated smoothed value, but a likely error range as well:
Apparently NH snow cover declined sharply during the 1980s, then increased somewhat in the early 1990s (possibly due to the Mt. Pinatubo volcanic explosion), was reasonably stable from about 1995 to 2003, and has since been again in decline. We can also smooth the data using a wavelet transform, which we can apply directly to the snow cover data rather than anomaly data. I’ll set the time scale to be much shorter than for the Savitsky-Golay filter, so we’ll get a look at some of the faster fluctuations from year to year:
There is of course more interannual variation in the wavelet smooth, because it’s tuned to detect that, but the overall picture is the same: a large decline during the 1980s, a smaller increase in the early 1990s, and a recent resumption of decline.
Wavelet analysis can show us not just the annual average NH snow cover, it can also quantify the amplitude of the annual cycle (the difference between peak and trough). Here’s a plot of the semi-amplitude (which is just half the amplitude):
Clearly, although average snow cover has declined over the years, the annual cycle has gotten bigger. This tells us that the decline isn’t the same throughout the year, instead there’s a seasonal pattern to it. In particular, with the cycle amplitude growing while the annual average declines, we can expect that most if not all of the decline in NH snow cover is occuring during the summer minimum.
We can further delineate this by computing annual averages for each season separately. Let’s take the usual climatological seasons, Dec-Jan-Feb for winter, Mar-Apr-May for spring, Jun-Jul-Aug for summer, and Sep-Oct-Nov for fall. Here’s the average NH snow cover anomaly over time, for the winter season:
There’s been almost no change over the years; the trend in wintertime NH snow cover isn’t statistically significant. But for the spring season, it’s a different story:
There’s quite a strong (and significant) trend, snow cover declining by about 64,000 km^2 per year. For summer the trend is even stronger:
Summertime snow cover in the NH has been declining at an average rate of about 101,000 km^2/yr. For the fall season, we once again note no statistically significant decline:
The overall picture is now clear: during fall and winter, NH snow cover hasn’t really shown any trend over the last four decades, but in spring and summer it’s declined significantly, with its fastest decline during summer.
It seems to me that this sequence of events fits the pattern expected from global warming. Higher average temperatures cause earlier and greater snow melt, leading to significantly less summertime snow cover. But they also increase the total atmospheric water vapor, allowing more snowfall during winter to compensate the decrease caused by snow melt, leading to no net change in fall/winter snow cover. This is just speculation on my part, but it makes sense to me.
This much is beyond doubt: the effect of snow albedo on climate forcing is far greater during summer than winter, because that’s when the hemisphere receives the greatest sunlight and the impact of albedo is most important. When a region is in total darkness, albedo has no affect at all! Hence the decline in summer snow cover may have been a significant factor in the rapidly rising temperatures of the northern hemisphere land areas.
82 responses so far ↓
Rainman // April 9, 2008 at 3:32 pm
Hmm… now this is interesting.
I’ve been doing further research at the sites suggested by others, and was surprised at how little the temp drops when in an ice age (~4C). Given the NH is warmer than SH in general (attributed to lower land mass, etc), the albedo of the NH would seem to be a driver for ice age entry/exit.
I’m still scratching the surface of this, but other than earth’s procession, what are the main drivers for ice ages? (they don’t occur every procession min/max)
[Response: The main astronomical cycles are obliquity (the tilt of the earth's axis), precession (not the usual astronomical definition, but the angle between the equinoxes and the perihelion of earth's orbit), and eccentricity. I post on the topic here.]
John Mashey // April 9, 2008 at 5:27 pm
Nice analysis, and given that we ski in Canada, I’m pleased to see the Winter snow is hanging in there.
On the other hand, maybe it’s time to start planning on covering Greenland or Northern Canada with aluminum foil… I once back-of-the-enveloped that 3 years’ world aluminum production would do Greenland, and of course, there are most likely better ways … but seriously, has anyone computed how much Northern land area needs to be covered with a good reflecting material to raise the overall albedo enough to be noticable?
David B. Benson // April 9, 2008 at 5:30 pm
Tamino aka “Hansen’s Bulldog wrote “But they also increase the total atmospheric water vapor, allowing more snowfall during winter to compensate the decrease caused by snow melt, leading to no net change in fall/winter snow cover.” with ‘they’ referring to ‘higher average temperatures’.
My understanding is that water vapor responds to temperature changes in less than two weeks. So I think you need to demonstrate higher average temperture during the fall and winter seasons during the latter part of the series in comparison to the earlier part.
dhogaza // April 9, 2008 at 6:02 pm
You don’t need increased winter snowfall, you just need enough snow falling on enough cold days to cover the bare earth exposed during summer.
Snow cover is extent, two-dimensional, km^2, no?
The situation’s the same as with the arctic ice cap, yes, extent has been decreasing in summer, and the volume year-round has been decreasing steadily in recent decades, but winter refreeze means that the extent during winter hasn’t been steadily decreasing. It’s just *thin*, not absent :)
Dano // April 9, 2008 at 6:38 pm
The last three places I’ve lived have had mountain ranges that supplied summer water -Sierra Nevada, Cascades and now here all have water managers who report increasing springtime snowmelt resulting in changing management regimes/paradigms.
Your analysis, Tamino, is yet another data point to draw upon, thank you.
Surely the denialists have a boilerplate answer for this quandary. Where is the kim bot’s automated reply routine?
Best,
D
dhogaza // April 9, 2008 at 7:05 pm
Snowpack is huge in the Cascades this year! Therefore, global cooling has begun!
How’d I do? :)
Nick Barnes // April 9, 2008 at 7:21 pm
It occurs to me that anomaly might be better expressed as a proportion. In the summer there is far less snow (the summer minimum is less than 10% of the winter maximum). It’s simply impossible for the summer anomaly to be (say) -5 million square kilometres, whereas that would be clearly possible in winter. How would the anomaly analyses look if we measured anomalies as proportions of the seasonal average?
Nick Barnes // April 9, 2008 at 9:03 pm
This isn’t right. Albedo affects both absorption and radiation. A white or reflective surface exposed to a clear night sky will lose less heat than a black surface.
I don’t think it makes much difference to your argument, though.
Paul T // April 9, 2008 at 9:13 pm
Are there any other implications from the declining summer snow besides albedo and precipitation, like say ocean currents in the Pacific or Atlantic? Or am I way off base here?
S2 // April 9, 2008 at 10:05 pm
Nick Barnes:
Actually I think that’s wrong - there’s no reason why a white body should lose less heat than a black body by radiation. The term “black body” refers to it’s ability to absorb, not emit.
Having said that, ice can act as a “blanket” if the seas underneath are warmer - so winter sea-ice probably slows down heat loss from the oceans - but this isn’t an albedo effect.
[Response: If I'm not mistaken, Kirkhoff's law states that the absorptivity and emissivity are roughly equal, so a white body both absorbs and emits less radiation.]
S2 // April 9, 2008 at 10:25 pm
I thought Kirkhoff’s law applied to electronics?
I admit that I could be wrong, but from my memory of physics there’s no good reason why a white body should emit less radiation than a black body at the same temperature.
It’s many years since I studied this, though.
At equilibrium a white body will absorb less (and therefore emit less) than a black body, but the poles are hardly at equilibrium.
I think. :)
luminous beauty // April 9, 2008 at 10:47 pm
Some confusion here.
Kirkhoff’s Law is for absorption and emission of a gray body at thermal equilibrium. It doesn’t really deal with physical behaviors of different materials.
Emissivity for ice and deep water are ~0.98. Water slightly higher usually.
Deep water albedo is ~0.04. Ice albedo is ~0.95. Freshly fallen snow as high as 0.98.
Thermal conductivity of ice is ~4x greater than liquid water. It’s sole insulating characteristic is as a radiant barrier. Snow is better, because it is filled with air pockets.
Hansen's Bulldog // April 9, 2008 at 11:03 pm
The wikipedia entry would imply that Kirchoff’s law does apply. However, it occurs to me how it can be valid, and *still* snow would, under real-world conditions, exhibit very low absorption (high albedo) but not exhibit very low emission.
That reason is that the absorptivity/emissivity is wavelength-dependent. For shortwave (solar) radiation, the absorptivity and therefore emissivity could be extremely low, but for longwave it could be considerably higher.
Hansen's Bulldog // April 9, 2008 at 11:18 pm
Upon reflection, I realize that if absorptivity equals emissivity at all wavelengths, but is not constant as wavelength varies, then it’s not a gray body and Kirchoff’s law doesn’t apply.
How silly of me.
TCO // April 9, 2008 at 11:32 pm
Tam:
1. Nice analyses and discussion.
2. I think the moisture vapor feedback is more rapid than season to season.
3. Is there a seminal journal paper on this stuff or did you just go and do useful analysis on your own, that is publishable?
4. I think another way to express or think about this is something having to do with gradients and seasons. AGW tends to warm the Northern lattitudes more. but in the Winter, they are snow covered regardless. So the major impact is on erosion of the snow coverage in summer. This is somewhat non-intuitive given that AGW is supposed to hve more impact in winter than in summer. (although I’m not sure the records support that.) In any case the two gradients could be characterized mathematically. (sorry if this is akwardly expressed.)
[Response: The analysis is my own -- that's my job -- but I'd be surprised if noone has yet published essentially the same results in some journal somewhere.
The temperature records from far northern latitudes that I've seen do support greater warming in winter than summer. But that could still be related to less summer snow; if winter melt is increased, then the remaining snowpack would be thinner and more vulnerable to summer disappearance. But this too is speculation.]
Eli Rabett // April 9, 2008 at 11:51 pm
Exactly, the absorptivity in the IR is very high (~1) for just about anything. In the visible it varies, so what is affected is the absorption/reflection of sunlight.
G Kramm is still sticking his finger up his nose on this one.
Heretic // April 9, 2008 at 11:55 pm
Dhogaza had a point. The fact that the winter coverage has not changed does not indicate that more or less snow is falling (to know that, we need to know thickness). It is rather indicative of the surface extent of snow conducive conditions: air temp, available moisture and surface temp.
Considering how quickly water vapor is supposed to cycle, it seems unlikely that the low summer extent can lead to increased snow fall. Furthermore, we do not know if snow fall is really increased or not, just that winter coverage is stable. I guess it would be interesting to look at snowpack data and see how it correlates with coverage, i.e. whether a thin snowpack is consistently reflected as smaller coverage.
cce // April 10, 2008 at 12:09 am
You can generate maps using the GISTEMP website that show the strongest anomalies are at high latitudes over land during the northern hemisphere winter. http://data.giss.nasa.gov/gistemp/maps/
Ralph // April 10, 2008 at 12:35 am
Emissivity will vary with wavelength appropriate for the temperature. For 300K, you’re talking around 10 microns(long-wave infrared). For solar radiation, it’s around 550nm(green light).
Clean snow is absorbs little energy in the visible spectrum(80%) in the long-wave infrared range.
steven mosher // April 10, 2008 at 1:20 am
ahh. this snow job misses the next big debate
Look at how GISS-UAH and GISS-RSS and
GISS - (UAH+RSS/2) shapes up for march
and then guess where HADCRU will come into the mix.
I find this focus on monthly junk funny. It’s like blaming Katrina on AGW. pretty soon you know the weather will turn. and the coolists will crow. and then it will turn again.
How do you GOVERN when you know short term observations may prove you “wrong”
( see the scare quotes ijits)
JCH // April 10, 2008 at 11:33 am
“On the other hand, maybe it’s time to start planning on covering Greenland or Northern Canada with aluminum foil …” - John Mashey
I’ve suggested this sort of thing a couple of times on RC. Nobody says much. I think the west could pay African farmers to keep much of the Sahara bright white.
Because of tons of sunshine (and fertilizer), Alaskan vegetables grow to an astonishing size.
ejort // April 10, 2008 at 12:24 pm
Re: Emission versus Reflection
Albedo is reflection. It has nothing to do with
white/black/grey body emission so Kirchoff’s law doesn’t apply.
Materials behave very differently under the two different processes, see for example:
http://rammb.cira.colostate.edu/wmovl/VRL/Tutorials/GOES39/emissiv3.htm
http://rammb.cira.colostate.edu/wmovl/VRL/Tutorials/GOES39/emissiv4.htm
Boris // April 10, 2008 at 12:41 pm
I’m going to go out on a limb and say this is probably not caused by air conditioners in proximity to thermometers.
Gavin's Pussycat // April 10, 2008 at 1:22 pm
ejort:
Not true: albedo is what doesn’t get absorbed.
For a given wavelength, the percentage of incoming light that gets absorbed equals the percentage of the value given by Planck’s curve that gets emitted. Kirchhoff-Bunsen’s law.
E.g., heat up a glass test tube with a Bunsen burner. It doesn’t glow, because glass doesn’t absorb visible light. Dangerous :-)
For grey bodies, the percentage is a constant independent of wavelength.
Joshua W. Burton // April 10, 2008 at 1:39 pm
Albedo is reflection. It has nothing to do with
white/black/grey body emission so Kirchoff’s law doesn’t apply.
The point of Kirchhoff’s law is that reflection and emission/absorption are related, in just such a way as is needed to stop you building a workless heat pump. (Because then you’d use it to build a perpetual motion machine, wouldn’t you? Just a little one, I daresay. Nature can see your kind coming a mile off, and plans ahead.)
To be precise, a body in a thermal bath at its own temperature must neither absorb nor emit energy, when integrated over all angles and all frequencies, else you could move heat uphill with the right paint. Therefore, albedo plus emissivity must equal one: all the energy that comes in has to go out, and there’s no use taking photographs of your clay masterpieces by their own glow while they’re still in the kiln; all you’ll see is red. (Similarly, if you want to build an IR telescope and put it in orbit, you’d better have enough liquid helium onboard so that you’re not just imaging your own glowing mirror.)
Now, take the object out of thermal equilibrium — in the case of the earth, put it in a cold bath at around 2.7K, with a spatially isolated heat source at 5700K. Absorption and emission need no longer balance: the earth can heat up, or cool off. But the identity that albedo = 1 - absorptivity = 1 - emissivity still holds, where the first equals sign enforces the First Law of thermodynamics, and the second one enforces the Second Law.
ejort // April 10, 2008 at 3:02 pm
“Not true: albedo is what doesn’t get absorbed.”
and
“albedo = 1 - absorptivity = 1 - emissivity still holds,”
Ok, I take your points. Albedo is reflection. What isn’t reflected is absorbed. What gets absorbed is re-emitted.
My point was you shouldn’t mixup which laws
apply to which process.
Albedo is not thermal emission, it is reflection/scattering. You wouldn’t apply Plank’s law
to light reflected off a mirror. :-)
Aaron Lewis // April 10, 2008 at 4:33 pm
Bottom line: Under current conditions of global warming, snow in winter helps keep the soil warm. In summer, the snow melts and the soil is able to collect and store more heat.
This has special impact in permafrost soils where storing more heat means melting permafrost. Warmer soil in agricultural areas changes required cultural practices including irrigation and type and yield of crops.
Permafrost is frozen water. Melting permafrost allows water to drain into the oceans raising sea level. Melting summer snow means all of the water from the snow reaches the sea each year, changing water resource patterns
This analysis has very real and practical implications.
Gavin's Pussycat // April 10, 2008 at 4:39 pm
itself
Yes… beautiful argument. I had forgotten about that.
You don’t even need the ‘re-’. As long as the object itself isn’t changed, the emission spectrum (as a percentage of Planck) will equal the absorption spectrum (as a percentage of incident light).
Joshua W. Burton // April 10, 2008 at 6:49 pm
Albedo is not thermal emission, it is reflection/scattering. You wouldn’t apply Plank’s law to light reflected off a mirror.
Uh, sure I would. A mirror with albedo A, sitting in the dark at a temperature T, will emit spherical power (1-A)σT4 per unit area. This is the Stefan-Boltzmann law, derived by integrating the Planck distribution over frequency. Note that the albedo enters into the emission formula precisely because reflection and emission are not independent quantities, thanks to the laws of energy and entropy.
Now, snow is not as white near the earth’s emission peak (300K, deep infrared) as it is near the peak of the solar spectrum. So, as Nick Barnes says, it’s not trivial to work out how important snow’s whiteness is at night. But insofar as snow is white in the relevant frequency range, that whiteness does matter, even in the dark. High-albedo objects radiate inefficiently at night, as a necessary and complementary aspect of their reflective efficiency in the daytime.
Dano // April 10, 2008 at 6:50 pm
Because of tons of sunshine (and fertilizer), Alaskan vegetables grow to an astonishing size.
No. In the Mat-Su valley, it is because of good soil and long days.
Before petrochemical fertilizer the veggies were just as huge.
As for large-scale albedo projects, sure. Cover the surface with foil. Riiiight. I’m sure the biota will enjoy that immensely.
Best,
D
Hugh // April 10, 2008 at 7:56 pm
Are the Alaskan veggies as tasteless as Icelandic apples.
You see them in the shop and they have a real ‘Sleeping Beauty’ quality; size of a baby’s head and rosy red.
It’s all downhill once you bite them though, shame.
TCO // April 10, 2008 at 9:54 pm
Geek science question:
I am familiar with both SPECULAR and DIFFUSE reflectance. Are both of these considered part of the albedo?
Joshua W. Burton // April 11, 2008 at 12:34 am
I am familiar with both SPECULAR and DIFFUSE reflectance. Are both of these considered part of the albedo?
Yes. Both silvery objects and white ones can have an albedo arbitrarily close to 1.
Molnar // April 11, 2008 at 2:59 am
Your Mt. Pinatubo hypothesis is hard to resist given the timing, but I wonder if anyone has a theory on how the effect could persist to the extent that we are only now getting back to the pre-Pinatubo anomaly?
Alexander Ač // April 11, 2008 at 7:45 am
Dear Tamino,
I would have a comment to Your previous post regarding the rate of CO2 increase from Mauna Loa readings. There is an recent paper by Piao et al. (2008) from Nature, where they have found that during the autumn warming on the nothern hemisphere, increased temperature (compared to long-term average) increases respiration more than photosynthesis (thus off-setting the net carbon gain). While this is not the case during the spring. Could you separate the data in your 1st graph from the previous post on SPRING and AUTUMN months and see, if there is any difference between them? Based on the Piao et al. study the autumn (and especially autumn warmer) months should have seen larger inter-month CO2 increase than spring months (assuming that anthro CO2 emission are +- the same)…
Best, Alexander
ejort // April 11, 2008 at 10:48 am
”
>Albedo is not thermal emission, it is
>reflection/scattering. You wouldn’t apply Plank’s
>law to light reflected off a mirror.
Uh, sure I would. A mirror with albedo A, sitting in the dark at a temperature T, will emit spherical power (1-A)σT4 per unit area.
”
You’re mixing things up. :-)
The (1-A) is not part of Stefano-Boltzman’s law.
The (1-A) comes from discarding the solar radiation reflected by the Earth when considering how much is absorbed and then equating that to how much should be emitted.
If there’s no incident solar radiation (1-A) x 0 = 0 as Tamino originally said. ;-)
Joshua W. Burton // April 11, 2008 at 1:23 pm
No, you still don’t get it. The emissivity, which equals (1-A), is part of the Stefan-Boltzmann law for thermal emission, even in total darkness. The reason albedo enters into it is because albedo and emissivity have a fundamental connection, enforced by the 2nd law of thermodynamics.
ejort // April 11, 2008 at 1:45 pm
”
No, you still don’t get it. The emissivity, which equals (1-A), is part of the Stefan-Boltzmann law for thermal emission, even in total darkness.
”
We’ll have to agree to disagree then.
You seem to think thermal emission is somehow related to “reflection of darkness”. :-)
NOTE: I’m not arguing there’s no thermal emission,
I’m just saying it’s unrelated to the incident light (there is none) or the albedo.
I think the problem is you’re using mathematical equations rather than looking at the real physics.
The equations you’re using break down when there is no incident light. It is a 0/0 problem.
Albedo = Reflected Light / Incident Light
P. Lewis // April 11, 2008 at 2:12 pm
Then there arises the moot point that even at night the dark is not absolute (although the darkness will tend to a maximum on a cloudy moonless night).
And then there is the infra red …
BBP // April 11, 2008 at 2:19 pm
There will always be incident light (unless you somehow have a dark room at 0 Kelvin…)
Joshua W. Burton // April 11, 2008 at 2:49 pm
We’ll have to agree to disagree then.
Ahem. Sorry, no more time for this. Pulling rank.
Here are two of the best undergraduate texts, if you actually want to learn this stuff. Sorry about the prices; they cost about a third that much when I used to teach from them.
“Reflection of darkness” is a very evocative phrase to describe the necessary entropic relationship of thermal emissivity to reflectivity, by the way. To make sense of your metaphor, perhaps we’d think of it this way: dark objects are bad reflectors of light (low A), so they’re good “reflectors of darkness” (high 1-A=ε). As temperature increases, an imaginative person might say that the “darkness” (i.e., blackbody glow) grows more intense, and everyone emits more of it, but even in a hot kiln a dark object glows more than a reflective one, because of its higher ε.
I wouldn’t try that in front of a classroom, because it would confuse many more students than it would help, but if you find it a useful image to help remember the connection between thermal emission and albedo, run with it!
J // April 11, 2008 at 3:05 pm
I think ejort is slightly confused about how “albedo” is being used here. The hypothetical object in question has some particular albedo in the visible spectrum … which is, as he/she says, irrelevant in this dark room. But it also has some (different?) albedo in the IR … which in turn is related to its emissivity at the same lambda … and which is manifestly not irrelevant because the IR incident radiation is > 0 (unless you’ve managed to pull off some kind of really neat trick).
Actually, in the real world I’ve never heard anyone use the expression “albedo” to refer to spectral reflectance in the IR … but the terminology doesn’t really matter.
Hansen's Bulldog // April 11, 2008 at 3:14 pm
There are different uses of the word “albedo.” It can refer to the reflectance at a given wavelength of light, in which case of course it’s wavelength-dependent, or it can refer to the reflectance on incoming radiation which matches a particular light source (like the sun).
It can also refer to the reflectance of an object in an isotropic radiation field (equally illuminated from all directions), which is the geometric albedo, or it can refer to the reflectance of a planet under actual solar illumination conditions, which is the Bond albedo. This is different from the geometric albedo; for earth, the most reflective parts (the poles) are the least illuminated.
Climate science deals specifically with the Bond albedo, which is the reflectance of incoming solar radiation under actual illumination conditions (averaged throughout the year).
Nick Barnes // April 11, 2008 at 3:28 pm
As Eli pointed out, what really matters in the dark is the IR emissivity: neither the snow nor the land it covers is hot enough to emit anything at visible wavelengths.
And as Joshua pointed out, the IR emissivity is intimately - arithmetically - connected to the IR reflectivity (aka IR albedo). For fundamental thermodynamic reasons, emissivity plus reflectivity has to be equal to one, i.e. non-reflective objects have to be good emitters and reflective objects have to be poor emitters. How much an object emits at a wavelength doesn’t depend on how bright the environment is at that wavelength; only on how hot the object is and the emissivity at that wavelength.
I hope I’ve got this straight.
So what really matters is the IR emissivities of surface materials (snow, ice, sea water, soil, vegetation, soil, rock, etc). Eli asserts that they are all ~1. Has anyone got data for this?
J // April 11, 2008 at 4:14 pm
Emissivities for water, snow, ice, and vegetation are all very close to 1 in the 8-14 micron window. Dry soil is a bit lower.
There are lots of sources of data on this. Here’s just one:
http://www.icess.ucsb.edu/modis/EMIS/html/em.html
luminous beauty // April 11, 2008 at 5:18 pm
It isn’t the Stefan-Boltzmann Law that determines the relation of emissivity to reflectivity, but the relationship of a given material’s emissivity and reflectivity that determine the Kirchhoff equilibrium point as derived from S-B for that material.
Example; Ice is naturally highly reflective because of flaws in it’s crystalline structure. Without those flaws, it would be as absorptive as liquid H2O (in the visible spectrum). It is nearly as emissive (in the IR spectrum) as water, less a smidgeon only because it is usually colder.
(Natural) ice loses energy (IR) much more easily than it gains it from visible light because of albedo (gray body tending toward white). For liquid water the two are very close (near black body). Hence the generalized (across all frequencies) gray body Kirchhoff equilibrium temperature for (natural) ice is lower than that for water, given that the source of energy is mostly VL.
ejort // April 11, 2008 at 5:19 pm
”
I think ejort is slightly confused about how “albedo” is being used here.
”
I don’t think I’m confused, but you might be right judging by Joshua not getting my point?
If you go back to the original controversy:
”
When a region is in total darkness, albedo has no affect at all!
This isn’t right. Albedo affects both absorption and radiation.
”
Then my point is;
Yes, Albedo effects absorption and radiation/emission (I conceded it earlier), but it is irrelevant to Tamino’s comment because in his example there is nothing to absorb.
Although it is kind of moot (as suggested by BBP)
because of the third law of thermodynamics.
Even the “vacuum” of space radiates some energy.
P.S. “Reflection of darkness” was meant as a “proof by contradiation”. Inbound radiation of 0 Wm-2 has no entropy or energy making the 1st and 2nd laws pretty much irrelevant. ;-)
ejort // April 11, 2008 at 5:34 pm
”
Actually, in the real world I’ve never heard anyone use the expression “albedo” to refer to spectral reflectance in the IR … but the terminology doesn’t really matter.
”
I’d guess it is convention because the atomsphere (or ground) will absorb the Solar IR and so it doesn’t really contribute to the albedo?
Nick Barnes // April 11, 2008 at 9:59 pm
ejort:
Yes, Albedo effects absorption and radiation/emission (I conceded it earlier), but it is irrelevant to Tamino’s comment because in his example there is nothing to absorb.
But there is something (IR) to emit. And high albedo substances are poor emitters (inescapably, because of the absolute fundamentals of thermodynamics, as pointed out by Joshua). Knowing this, my original original point was to question whether the high albedo of snow is relevant in the dark. Specifically, whether a loss of snow cover, and a resulting reduction in average albedo, would result in greater radiative heat loss.
Eli and J have answered this point very well for me by pointing out that there is almost no difference between the *IR* emissivities of the different materials, despite the wide variations in their *visible* emissivities. I didn’t know that; it’s useful information about the properties of these particular materials which cannot be deduced from a thermodynamical approach to the system. A happy accident, if you like.
Have we done this entirely to death now?
Vic // April 11, 2008 at 11:30 pm
Tamino,
Thanks for your research. This is an interesting issue.
It can also explains the fast melt of permafrost. The relative higher snowcover in fall isolates well so summerheat can be better stored in the soil. In spring that heat can accellerate the melt proces of snow and permafrost.
The month to month correlations in snowcoveranomalies are high for summer but much lower for winter. This means that snow doesn’t stand long on area’s which makes the difference in winter. The rate of replacement should play an important role in it but less in summer.
Snowcover also correlates well with de NAO-index, especially in januari, februari, march and in summer.
@ John Mashey
I’v calculated that about 2% of land have to be covered (albedo = 0,7) to compensate for al GHG forcing since 1850.
JCH // April 12, 2008 at 12:35 am
“@ John Mashey
I’v calculated that about 2% of land have to be covered (albedo = 0,7) to compensate for al GHG forcing since 1850. …” - Vic
What do you mean?
Vic // April 12, 2008 at 8:17 am
JCH,
The question was how much landsurface needs to be covered with high reflected material.
It’s complex to compute this exactly because it depends on latitude and average cloudcover over that area has to be known.
I keep it simple and use global mean values for cloud albedo and irradiance (48% of 335 W/m2 reaches earth surface) . Normal landalbedo is set to 0,1 and I choose 0,7 for the albedo of reflecting material. This material absorps 96 W/m2 less at average conditions. The radiative forcing due to greenhouse gases is about 2 W/m2 (IPCC) . Hence approxemately 2% percent of earth surface need to be covered , i.e. 105 miljoen square kilometer (my former post was not correct in here). This means 7% of total landsurface.
JCH // April 12, 2008 at 2:23 pm
That’s a lot of land. Isn’t the earth’s land surface area 150 million sq km?
Also, since it’s receding, shouldn’t the pursuit be to replace lost ice cover: to maintain the earth’s balance between ice and ice-free?
wildlifer // April 12, 2008 at 6:25 pm
I left this on the open thread, but it hasn’t appeared. Has anyone yet addressed Asher’s latest, I’m looking for rebuttals :
http://www.dailytech.com/Reseacher+Arctic+Temperatures+Not+Especially+Warm/article10713.htm
Since it deals with Artic temps, I guess it’s appropriate here.
[Response: Linking to, and asking about, Grudd's published research is legitimate. Linking to the dailytech article is not; this is NOT a blog to advertise denialist propaganda.
Just an example of how misleading that article is: the title is "Reseacher: Arctic Temperatures "Not Especially Warm," but if you read the published research, the word "arctic" is nowhere to be found. It's about a temperature reconstruction for Tornetrask, Sweden only.
The paper also points out that max-density indicates no long-term trend, but the more usual indicator, tree-ring-width, does in fact indicate unusual recent warming. I'll leave it to dendrochronologists to settle the issue which is more meaningful.]
wildlifer // April 12, 2008 at 7:22 pm
Thanks. :-)
dhogaza // April 12, 2008 at 7:38 pm
Hmm … since the post was a cry for help with a rebuttal argument, and since the article misrepresents the published paper, what would you have him do? Copy part of the article here rather than link?
[Response: His first comment didn't mention seeking a rebuttal. I was mistaken to interpret his 2nd comment as an attempt to link to denialist propaganda; it was clearly an attempt to seek refuting evidence. Even after the 2nd comment I failed to realize this; my mistake, I must be having a cloudy day.]
Vic // April 12, 2008 at 11:04 pm
JHC,
The total landcover is ten times more.
It seems to me a good idea to replace ice- and snowfree area’s first.
If every user of internet prints the IPCC report a thousand times and spread it around the earth it would help. ;-)
grant czerepak // April 13, 2008 at 12:10 am
Too little data.
One moment you are explaining the trend is not linear and the next moment you are making an implied linear extrapolation.
Your conclusions are made to fit your theory.
[Response: I made no extrapolation whatsoever. I show undeniable statistical results from the data, I speculate in a few places but not much, and I made it quite clear what was speculation and what was straightforward. I didn't imply any extrapolation, you just made that up.
You're just picking nits in an attempt to sling mud. The weakness of your attempt embarrasses you.
I'm guessing this is a response to my comment on your blog, and to your rather ridiculous claims. I commented there because I took you seriously; that's a mistake I won't repeat.]
grant czerepak // April 13, 2008 at 12:24 am
You made a linear interpolation of data points that do not reflect a linear progression.
If the data curves draw a curve.
[Response: Once again you embarrass yourself. Do you know the meaning of the word "interpolation"?
The purpose of the linear regression is to demonstrate the presence or possibly the absence of a trend, and to quantify the average rate of change over the entire time span of the data. It does exactly that. I also stated quite explicitly "But the trend has not in fact been linear." As for showing a curve, what this?
Most readers here either have enough knowledge, or sufficient humility, not to make such ridiculous statements as yours.]
Zeke // April 13, 2008 at 1:08 am
Tamino:
I’m still trying to figure out the origin of the claim over at Grant’s blog that:
“89% of the IPCC data was gathered in Europe, 10% in North America and 1% in the rest of the world.”
Now, there is a realistic argument to be made that the temperature record has historically had a northern hemispheric bias, though this is corrected for reasonably well, but a “Europe” bias is a new one for me. My only guess is that he looked at the WGII SPM graph on observations of biological systems effected by climate change. In this case, there is a reasonably strong European bias in the data, though observations of biological systems are in no way central to the theory of AGW.
As far as your post on Grant’s blog, while spending “a couple of years” studying the science might be necessary for detecting sophisms, that argument doesn’t always go over well. Recall Gavin’s infamous flop when he made a similar point to the audience at the E^3 debate against Lindzen and Crichton.
[Response: There's a blogger on wordpress, I don't recall the name, who has made repeated posts about the "European bias" in IPCC data; I strongly suspect that's where he got it from. You might be right about the WGII SPM.
I suggested to him that he needs a couple of years to understand the science, because his post gave me the impression that he was sufficiently open-minded and intelligent to do so. I was mistaken.]
dhogaza // April 13, 2008 at 1:24 am
I suspect this might be a result that surface temp records have been kept in europe for a long time, longer than here in North America?
And, um, that no other data exists (cough, cough)?
grant czerepak // April 13, 2008 at 2:54 am
The trend has not in fact been linear. Hmmm.
Since I am not knowledgable or humble, humor me and show the curve for the summer data.
If I am incorrect state it and explain why. Use reason and logic. That goes for luminous beauty as well. I liked your trendy put down lb, but that is all it is. Isn’t it convenient to advocate self-doubt when you are questioned regarding your own certainty?
I don’t believe in “leaving it to the professionals” because I believe in that gawd awful thing called democracy and free speech. I am agnostic about this issue. I neither accept or deny at this point. All I know is science made the tools that put us here using more resources, venting more carbon and producing more waste. The same mindset cannot get us out.
We cannot look at the world through the eyes of Descartes with the certainty that we are masters and proprietors of nature. That is the Dunning-Kruger Effect exhibited by the scientific community including climatologists and most of human society. Are the so called solutions by either side not going to create even more problems? Maybe that concerns me more than whether I agree or disagree with the evidence.
[Response: Are you some kind of masochist? This comment of yours is the most embarrassing of all. You tried so hard to criticize this post but only succeeded in making a fool of yourself, so you're trying to change the subject with a bunch of mumbo-jumbo. The most embarrassing part is that you're deluded enough to believe it makes you look smart. Think again.]
grant czerepak // April 13, 2008 at 5:13 am
What you are doing is speaking louder than what you are saying.
I think you are probably an intelligent person, but up to this point you won’t give me the benefit of the doubt that I have been reading the IPCC data before you suggested it. Actually, I think my seven years of university trumps yours. I worked with scientists for all of those years and I know very well how human scientists are. I’ve seen the influence of vested interests.
The summer data is a curve. It has only 40 data points. I don’t think this is good evidence. But you want to evade that. Why don’t you address it?
I talk outside your field and you call it mumbo-jumbo. You talk outside of my field and I step up to the plate. I say, “I hear you, but I am not pursuaded.”
Do you think I am ready to depend on a bunch of technocrats like you with no plan as to what to do when the world says “go”? Are we going to ruin the world economy with mega projects that may turn out to be a bunch of white elephants? If you have ever studied the history of this century you would know that the world is littered with dramatic failures of science and technology. There are variables that we cannot account for, so start seriously thinking about what the cost to the world will be before the judgment comes in.
All I see right now with AGW movement is the readiness to trip over the starting line and plant our faces in the dirt of a pastoral myth. What I see in the Climate Change advocates is the readiness to breathe the dirt of a progress myth. Irregardless of the evidence, it’s lose-lose.
JCH // April 13, 2008 at 5:27 am
Vic, total lay person here, so I’m not used to dealing with these large numbers, but is not this site stating the earth’s land surface comes to approximately 150 million sq km:
http://hypertextbook.com/facts/2001/DanielChen.shtml
Maintained in white, what continent(s) would accomplish your calculation?
grant czerepak // April 13, 2008 at 9:51 am
In conclusion, you used a linear regression and you don’t know the definition of interpolation. Second, you should have been using a non-linear regression to analyze the data. Consequently, you are giving your readers a false impression that the data extrapolates linearly downward.
For all your statistical gymnastics you are a lightweight.
[Response: I'm a professional mathematician. My specialty is the statistical analysis of time series. I've authored scores of articles in the peer-reviewed scientific literature. The scientific community -- my peers -- consider me a heavyweight. Further "debate" with you serves no purpose; you don't have the knowledge to contribute anything useful, you're unwilling to learn because you're unwilling to admit your own ignorance, and delivering the "smackdown" on you is just too easy.
When I pointed out that your claims about the IPCC reports were mistaken, how painfully embarrassed must you have been to come here, make so many truly infantile statements about statistical analysis, repeat them even after being corrected, and refuse to stop embarrassing yourself -- all because you're desperate to save your giant ego. You've only proved that you're a petulant child. Go away, and let the adults continue our conversation.]
Julian Flood // April 13, 2008 at 11:53 am
Vic wrote:
quote I’ve calculated that about 2% of land have to be covered (albedo = 0,7) to compensate for all GHG forcing since 1850. unquote
Mitigation is all very well, but there are better methods than covering the land. Might I suggest you look at the other 70% of the world’s surface and consider Salter and Latham’s proposal for upping cloud condensation numbers using wind-powered trimarans? Non-polluting, able to be switched off at will, it is well within current tech levels.
I’d be very interested in your calculations of how much ocean surface would need to be covered by strato-cumulus cloud to offset all global warming so far: my numbers keep coming out ridiculously low.
http://www.mmm.ucar.edu/people/latham/
Luminous Beauty: you write knowledgeably about emissivity. You don’t happen to know the difference in seawater emissivity when ruffled by wind and when completely still? And how much ocean would have to be ruffled to offset warming? Would smooth water cool less during darkness? The stuff available on the web is very dense and I can’t pick my way through it.
TIA.
JF
Hank Roberts // April 13, 2008 at 3:59 pm
Worth reading:
http://www.openthefuture.com/2008/04/the_big_picture_resource_colla.html
TCO // April 13, 2008 at 4:40 pm
Certainly it’s possible that resources will collapse, but the previous over-predictions by the Club of Rome, make me take such comments skeptically. I’m concerned given the previous invalid predicitons and given that the peopel making these predictions are generally leftist and their prescrptions for dealing with the problems are leftist. Sure…they might be right. But I realize they have a conflict of interest to guide them towards supporting the statements they make.
Hansen's Bulldog // April 13, 2008 at 4:59 pm
It’s probably best to take discussion of resource limitations to the open thread. My fault for not saying so earlier.
Vic // April 13, 2008 at 10:18 pm
JHC,
Thanks for your correction and helping me to solve this bug. Landsurface is indeed about 150 million sq km. However, the partial landcover with high reflective material is still 7%.
TCO // April 13, 2008 at 10:46 pm
Maybe we could just put a big mirror or shade or something like that in space.
Hank Roberts // April 13, 2008 at 11:44 pm
For subscribers to Jim Baen’s _Universe_
http://baens-universe.com/
don’t miss a good article in this month’s online edition by David Brin.
Nonsubscribers — try it. Good stuff.
Long title: “Becoming Stewards of Our World: The Great Theme of the 21st Century, Part Two, Editing the Sun: A Way Out Way Out”
He goes through many of the suggested options.
And — teaser — he writes:
“I’ll describe work I’ve done with Lowell Wood, Ken Caldiera and others on a single, concrete proposal —keeping the polar bears from going extinct. We’re preparing this work for publication now.”
They propose to
“… reflect mostly ultraviolet … energy, which heats when absorbed.
This describes a scientific experiment, designed to understand the complex climate system, not the beginning of an engineering project.”
Admirable idea, I hope. Serious authors with real credentials writing it. No mention therein of where to watch for the coming publication.
Watch the skies ….
Brian D // April 14, 2008 at 12:19 am
TCO:
Oddly, things that amount to that have been suggested. One that comes to mind is seeding the atmosphere with more sulphate aerosols in the hopes of increasing “global dimming”. It’s cheaper than the mirror (and was proposed by a more credible source), but still amounts to climate engineering.
It’s amazing the lengths people will go to rather than have their favorite blankie (cheap oil) taken away, isn’t it? Especially when the suggestion is of such huge magnitude and expense that committing to it is basically the same as inaction (that is, it’ll have unforeseeable consequences, long delays, lots of protesting, and little will get done).
By presenting arguments like that, it’s easy for delayers to bring up two of their favorite friends: The Straw Man and the False Dilemma. By framing their poor option as the only alternative, they can project its failings onto other, more legitimate courses of action. You can already seethis technique being applied to biofuel (”because corn ethanol is made from food, and we’re seeing high corn prices, ALL biofuel, regardless of source, must cause famine”).
One wonders how long it’ll take before the public realizes the delayer tactic for what it is: Poor logic that supports a philosophy they should have outgrown by now.
(Apologies for both the handwavy approach and the apparently-obnoxious tone. No hostility is intended here, but I don’t have the time right now for proper rigor or tone-of-voice corrections. Sorry.)
grant czerepak // April 14, 2008 at 12:38 am
I think the ego, petulance and childishness are your traits, Tamino. It is obvious in your demands for deference and reaction to my simply and honestly questioning the analysis of the data. And I know a lot about data. I’ve worked with terabytes of it.
You made a mistake in this analysis. You know it. And knowing it you resorted to a personal attack instead of correcting your error.
You haven’t done me a bit of harm although you obviously want to. You have only hurt yourself and the cause you support.
[Response: When you came here you had a real opportunity to learn. You could have gained some insights not only into what the data are telling us, but some of the methodology (both simple and advanced) used to glean those insights, from a professional working in the field. Instead you chose to offer petty criticism. And you simply refuse to acknowledge that you're wrong, in spite of the fact that your claims are so idiotic that even my most ardent adversaries (and there are quite a few who are regulars here) won't come to your defense. That's because they know that agreeing with you will make them look like idiots too.
You're also an outright liar when you claim to be "honestly questioning the analysis." From the start you tried to ridicule it. You only made yourself ridiculous with the attempt.
Everybody gets it. Except you. You have made yourself into a laughingstock.]
jp // April 14, 2008 at 1:59 am
Enough from this grant czerepak already. He’s a bigger idiot than Anthony Watts.
At first it was good for a laugh. Now he’s just a bore. You owe it to your readers not to subject us to this.
grant czerepak // April 14, 2008 at 4:19 am
You’re a single issue fanatic guilty of intellectual dishonesty and scientific orthodoxy.
You’re analysis and conclusions regarding this pitiful dataset are crap.
And your sacred and intensely dry IPCC data is about as empirical and accurate as the Farmer’s Almanac. Climatologists can measure, but their record for prediction, which is the hallmark of science, is abysmal.
So, now what do I wait for? The Thought Police?
[Response: Now you've turned into a raving lunatic. I didn't think it was possible for you to make yourself look more ridiculous -- but you found a way. JP is right, it's time for you to go.]
Nick Barnes // April 14, 2008 at 8:40 am
Many thanks to J for his link to the MODIS UCSB Emissivity Library. From that page, the critical piece of information:
Snow is unusual in that it has a high reflectance in the solar (visible) region where most of the downwelling energy is during the day, and a very high emissivity in the thermal region.
Note the word “unusual” in that sentence. My expectation of snow being a more “usual” material is what prompted my point about albedo.
Back to Tamino’s very entertaining smackdown now. Watching someone with that level of ignorance claiming that Tamino “doesn’t know the definition of interpolation”. Brilliant. You could charge money for this.
Hank Roberts // April 14, 2008 at 2:28 pm
Mr. Czerepak makes more sense today on his own turf. While he hasn’t understood the basic physics, he does understand how politics screws up responses to systems problems.
Note this on his page today:
” Will the solution factories produce the environmental equivalent of an Amazon, Ebay or Google? Or will we do the more likely thing? Treat the symptoms instead of improving the health of the planet.”
This — give him credit due — is a fundamental observation. It’s from system dynamics. You can find the same from Donella Meadows.*
IT people understand in their bone marrow that managers push leverage points in the wrong direction, and patch symptoms ignoring and increasing problems. That’s IT.
He hasn’t understood the basic physics — but neither have most of us. Remember the long, long pair of threads over at RC where a few patient people worked at finding words to give a clue hollw those photon thingies interact with some wiggly molecule shapes.
We take the quantum mechanics underlying radiation physics on trust. Using it we get the right answers — we in fact get the whole semiconductor industry on which all the computers are now based.
Anyone who believes the math that led to semiconductors is, eventually, going to believe climate physics works — not because it ‘makes sense’ that this is how the world works. Because it describes reality, in math, well enough to build on.
———————
* Here’s a wonderful Donella Meadows article I never expected to see again, someone posted it online:
http://www.slideshare.net/moJoe/it-seemed-like-the-thing-to-do-at-time-state-of-mind-and-failure/
Here’s the Leverage Points article — if you haven’t read this, please do:
# ^ Donella Meadows, Leverage Points: Places to Intervene in a System , 1999 http://www.sustainabilityinstitute.org/pubs/Leverage_Points.pdf
May I humbly suggest not pissing people off just because they piss us off, and not yelling at people just because they yell?
Some people who do give a damn have short fuses and little patience. Don’t lose them by helping them make the wrong choices here.
Don’t push the wrong way when you find you have leverage.
None of us are sensible on all points of discussion.
Debate is for setting people off.
Science is for understanding how the world works.
Maybe we _do_ need a bar down the street where we can all go jam after “work” here.
[Response: Hank, you're one of the most valuable readers I've got. You're intelligent, well informed, and you've often pointed me to resources I wasn't aware of that I consider extremely valuable. You're a real treasure.
But I don't agree. From his first comment here, he's done nothing but make truly idiotic attempts to ridicule this post. It's clear that he lacks even the most basic understanding of data analysis, yet he kept insisting, staunchly refusing to admit his ignorance. Seriously, when it comes to mathematical analysis this guy makes Anthony Watts look like Stephen Hawking. There are a lot of smart people who don't know beans about mathematical analysis, but they have enough brains not to make infantile attempts to "correct" those who do.
It's also quite clear that he was carrying out a personal grudge, it was an attempt to discredit me personally. Either he wanted revenge or to recover his extremely fragile ego.
His blog makes the ludicrous claim that the IPCC reports are bogus because 89% of the data come from Europe, 10% from N. America, and a mere 1% from the rest of the world. This was his response to my pointing him to the IPCC reports when he asked for more scientific evidence.
All of which argues very strongly against his critical thinking skills. In my opinion, he's proven himself unwilling to listen to reason but willing to sling mud on topics about which he knows less than nothing. I didn't "lose him" -- he got lost all by himself.]
JCH // April 14, 2008 at 2:42 pm
Vic, so by your calculation, 10.5 million square kilometers of white equivalent would have to be added to the existing 15 million square kilometers of white?
And that would essentially offset the GHGs emitted by mankind to date?
Hank Roberts // April 14, 2008 at 6:07 pm
Tamino, no argument with your perception and closure there.
Everything I wrote below the link to
http://www.sustainabilityinstitute.org/pubs/Leverage_Points.pdf
wasn’t a comment on your point of view (my bad, not clear); I meant that as cautionary to myself and others to avoid feedback whining.
Some mixes are hypergolic, and saying ‘no more’ is certainly appropriate.
Point intended: I was surprised to find the sustainability/leverage perspective there. I would guess the fact that people often push the wrong way when they find they have some leverage gets rediscovered fairly often, and by people from all sorts of different viewpoints/biases/belief systems.
Nothing I read here from him gave evidence of that level of clarity. Missionaries are more fundamentalist abroad than at home, I think, and we got Witnessing rather than curiousity.
And enough of that!
pathlesswood // April 15, 2008 at 3:32 am
I think as uninformed as grant czerepak may have been it didn’t warrant the treatment he was given by by demeaning and labeling him. If we’re going to win over lay people we’re going to have to be pretty patient.
That aside, apparently there is an engineer working on developing a mirror swarm–millions of them–that he wants to put in orbit between the sun and the earth. I’m looking for the link.
Barton Paul Levenson // April 15, 2008 at 4:51 pm
grant czerepak writes:
When did scientific orthodoxy become a crime? I do go with the people who say the speed of light is a real limit, mass can be converted to energy and vice versa, and light propagates by an inverse-square law. Is there something morally wrong in doing so?
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