Why Is Winter Snow Extent Interesting?

Guest post by Steven Goddard

Several people keep asking why am I focused on winter snow extent.  This seems fairly obvious, but I will review here:

  1. Snow falls in the winter, in places where it is cold.  Snow does not generally fall in the summer, because it is too warm.
  2. Winter snow extent is a good proxy for winter snowfall.  Snow has to fall before it can cover the ground.

So what about summer snow cover?  Summer snow cover declined significantly (from the 1970s ice age scare) during the 1980s, but minimums have not changed much since then.  As you can see in the graph below, the overall annual trend since 1989 has been slightly upwards.

click to enlarge

Data from Rutgers University Global Snow Lab

Note in the image above that there has been almost no change in the summer minimum snow extent since 1989, and that the winter maximums have increased significantly as seen below.

Summer snow cover is affected by many factors, but probably the most important one is soot, as Dr. Hansen has stated.

The effects of soot in changing the climate are more than most scientists acknowledge, two US researchers say. In the Proceedings of the National Academy of Sciences, they say reducing atmospheric soot levels could help to slow global warming relatively simply. They believe soot is twice as potent as carbon dioxide, a main greenhouse gas, in raising surface air temperatures. … The researchers are Dr James Hansen and Larissa Nazarenko, both of the Goddard Institute for Space Studies, part of the US space agency Nasa, and Columbia University Earth Institute.

http://news.bbc.co.uk/2/hi/science/nature/3333493.stm

The global warming debate has until now focused almost entirely on carbon dioxide and other greenhouse gas emissions, but scientists at the University of California – Irvine, suggest that a lesser-known problem – dirty snow – could explain the Arctic warming attributed to greenhouse gases….The effect is more conspicuous in Arctic areas, where Zender believes that more than 90 percent of the warming could be attributed to dirty snow.

http://www.scienceagogo.com/news/20070506202633data_trunc_sys.shtml

In summary, winter snowfall is increasing and currently at record levels, and summer snow extent is not changing much.  Earlier changes in summer snow extent were likely due primarily to soot – not CO2.

Why Is Winter Snow Extent Interesting?

Several people keep asking why am I focused on winter snow extent.  This seems fairly obvious, but I will review here:

1. Snow falls in the winter, in places where it is cold.  Snow does not generally fall in the summer, because it is too warm.

2. Winter snow extent is a good proxy for winter snowfall.  Snow has to fall before it can cover the ground.

So what about summer snow cover?  Summer snow cover declined significantly (from the 1970s ice age scare) during the 1980s, but minimums have not changed much since then.  As you can see in the graph below, the overall annual trend since 1989 has been slightly upwards.

Data from Rutgers University Global Snow Lab

Note in the image above that there has been almost no change in the summer minimum snow extent since 1989, and that the winter maximums have increased significantly as seen below.

Summer snow cover is affected by many factors, but probably the most important one is soot, as Dr. Hansen has stated.

The effects of soot in changing the climate are more than most scientists acknowledge, two US researchers say. In the Proceedings of the National Academy of Sciences, they say reducing atmospheric soot levels could help to slow global warming relatively simply. They believe soot is twice as potent as carbon dioxide, a main greenhouse gas, in raising surface air temperatures. … The researchers are Dr James Hansen and Larissa Nazarenko, both of the Goddard Institute for Space Studies, part of the US space agency Nasa, and Columbia University Earth Institute.

http://news.bbc.co.uk/2/hi/science/nature/3333493.stm

The global warming debate has until now focused almost entirely on carbon dioxide and other greenhouse gas emissions, but scientists at the University of California – Irvine, suggest that a lesser-known problem – dirty snow – could explain the Arctic warming attributed to greenhouse gases….The effect is more conspicuous in Arctic areas, where Zender believes that more than 90 percent of the warming could be attributed to dirty snow.

http://www.scienceagogo.com/news/20070506202633data_trunc_sys.shtml

In summary, winter snowfall is increasing and currently at record levels, and summer snow extent is not changing much.  Earlier changes in summer snow extent were likely due primarily to soot – not CO2.

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As you can see in the graph below, the overall annual trend since 1989 has been slightly upwards.
And what is R^2 for that graph?

Quite possible, however temperatures seem to be falling on landmasses as well and so the soot problem might turn out to be a good thing.

Steve Goddard

Just to be clear and avoid getting off on irrelevant tangents, snow cover did decrease from 1970 through 1989. Winter snow cover has returned to the unusually high levels of the 1970s. Summer snow cover has not returned to 1970 levels, but has not declined since 1989.

terry46

It is interesting how Henson tries to do the global warming spin.If the first theory doesn’t work then change theory.Folks these people could care less about what is really happening .The planet is cooling .But this goes against thier theory and goverment control.

Eddie

Could we get a close up view of the summer snow extent, like we did for the winter to see what tend looks like over the same period?

Leo G

Soot – mostly man made. yet somewhat easy to cleanup. does not stay around for hundred years, washes out with the melting. tackle this first, then see where we are….IMHO

JJ

The X axis in the first graph is mislabeled. Are those weeks? Can you show data from 1970 -present?

Is the first graph the one you meant to accompany this post? It doesn’t match the description.
PS. I just woke up, so maybe my brain ain’t workin’ yet.

pauly

‘When you’re in a hole, stop digging’ is a sound piece of advice.

Keeps deep frost away from the ground surface. Any farmer will know benefits of the winter snow cover.

John Phillips

We may be reaching a tipping point for the next glacial period. Humans are surely to blame. I just haven’t quite figured out how yet.

So there is more humidity in the Northern atmosphere during winters – so what?
That is doing what in relation to climate change?
It feels like reading the coffee pot – after having had one coffee, only.

Tenuc

Zender had a little lamb,
Its fleece was black as soot.
And everywhere that Zender went,
It’s sooty foot it put.

Summer snow cover declined significantly (from the 1970s ice age scare) during the 1980s,

The 1970s ice age scare caused snow cover to decline??

Steve Goddard

Leif,
Please feel free to do any statistical analysis you want, and share the results with us. If you want to repeat for the last 10 years that would also be appreciated.

Steve Goddard

The first graph X-axis shows weeks since 1966. It is pretty easy to pick out winter maximums and summer minimums.

Caleb

Expanded winter snow-cover must increase the albedo-effect. I’d like to see a discussion by people wiser than myself about what the difference might be.
I have some questions regarding the effect the bounced-back sunlight would have on the temperature of the atmosphere.
I assume that when snow reflects sunlight the sunlight doesn’t change into infrared waves, but remains the same long(?)-wave radiation it was on the way down. Therefore it would not “excite” CO2 on its way out. Is this assumption correct?
Does such long(?)-wave radiation warm the atmosphere at all, as it passes through?
If it does, would not the albedo-effect increase the warming of the atmosphere, because the light would warm on its way in, and also on its way out?
If this was true then, even as expanded snow-cover reflected a lot of heat back into outer space, we might see some slight warming of the troposphere. This might lead to the false impression things were getting warmer, even as we lost a lot of heat to outer space.
Are Oxygen and Nitrogen warmed at all, when sunlight passes through them?
If my ideas are way off base, I don’t mind being educated in the slightest. Thanks in advance.

Steve Goddard

jj,
Here is the entire Rutgers weekly data set going back to 1966.
https://spreadsheets.google.com/oimg?key=0AnKz9p_7fMvBdHBkREJtSmNlbm9xNnlza0JEcXUwZ2c&oid=2&v=1266508331457
Note the near record maximum on the right edge.

Steve Goddard (07:45:02) :
Please feel free to do any statistical analysis you want, and share the results with us. If you want to repeat for the last 10 years that would also be appreciated.
Come on. You have that data handy. And have software [Excel?] to put in the trend line. Just ask it for R^2 to gain some credibility.

Richard Telford

The data start in 1966. So why does your analysis starts in 1989?

MinB

I notice that you only cite NH snow extent. What does SH look like?
Does measuring snow extent give any indication of temperature trends in Arctic and Antarctic? Or is this more of a measure of mid-latitude variation?
What would slope for winter snow cover look like without 2010, i.e., how much flatter might it be?

DirkH

“Christian A. Wittke (07:38:51) :
So there is more humidity in the Northern atmosphere during winters – so what?
That is doing what in relation to climate change?”
The post doesn’t talk about “humidity in the Northern atmosphere”. How do you conclude that the humidity has risen? And while we’re at it, do you think that the mean humidity has risen? The peak humidity? Both? In which layers of the atmosphere? Any idea?
Or have you been confused by The Time with their “In the meantime, warmer air could be supercharged with moisture and…”
at
http://www.time.com/time/health/article/0,8599,1962294,00.html?xid=rss-fullhealthsci-yahoo
(which was pretty hilarious, i mean, SUPERCHARGED WITH MOISTURE. Like, more than 100% – which usually leads to precipitation, even when The Time doesn’t notice.)

Tom P

Leif Svalgaard (07:16:08) :
I was going to write something about fish and barrels, but the analogy rather breaks down when the fish start shooting themselves.

Henry chance

Snow cover is God’s gift to winter wheat fields. It is so many times better than mere rain fall.
As we read about the permanent dustbowl and reality shows us great ground cover for wheat.
Wheat can grow in the subsoil zones when covered by insulating snow.

Ralph

Ah ! So the snow was not rotten, ıt was dırty !!
.

John Innes

For coal-fired power stations, and perhaps to a lesser extent for other soot-generators, it should be cheaper to reduce the soot emissions than to extract and sequester the CO2 generated and emitted. Electrostatic precipitation has a head start, but CO2 separation and sequestration is only just out of the starting box in recent years. Hohlfield observed in 1824 that an electric discharge cleaned dust laden gases, and not too many years later, Lodge, and later Cottrell made and installed practical dust precipitators for smelter fumes. In 1935, Penney announced the development of the Precipitron, with a major reduction is size and voltage and an improvement in efficiency. This horse is already half way to the finish line.
Surely we can work from this as a starting point, and get more bang for our warming reduction buck by reducing soot instead of CO2? For a start, simply slowing the exhaust gas velocity through larger precipitators would reduce soot emission. It should be a simple matter to calculate the improvement that can be achieved per dollar spent, even without new developments. Considering the millions of dollars being thrown at CO2 studies, let alone action, we could not only be reducing AGW right now, if in fact it exists; we could reduce real pollution and breathe cleaner air. What were those numbers for coal-fired plants in construction or planned, again?

DirkH

“Caleb (07:47:41) :
I assume that when snow reflects sunlight the sunlight doesn’t change into infrared waves, but remains the same long(?)-wave radiation it was on the way down. Therefore it would not “excite” CO2 on its way out. Is this assumption correct?”
Yes. Only you got the “long” wrong – the longwave part of the spectrum we usually talk about here is the Longwave Infrared that is absorbed by CO2 and to a larger extent by water vapour, > 1 mikrometer. Visible light has shorter wavelengths, around 350nm IIRC.
“Does such long(?)-wave radiation warm the atmosphere at all, as it passes through?”
No, not in a significant way, as it is not absorbed.
“If it does, would not the albedo-effect increase the warming of the atmosphere, because the light would warm on its way in, and also on its way out?
If this was true then, even as expanded snow-cover reflected a lot of heat back into outer space, we might see some slight warming of the troposphere. This might lead to the false impression things were getting warmer, even as we lost a lot of heat to outer space.
Are Oxygen and Nitrogen warmed at all, when sunlight passes through them?”
No interaction between visible light and O2 or N2, otherwise air wouldn’t be transparent for visible light. So visible light that is reflected e.g. by snow will go outwards. There might be refraction by water droplets, so clouds will diffuse visible light. In the absence of clouds, the light reflected by snow (or white roofs, or any part of the surface) will just radiate into space without warming anything significantly.

Matt

Leif,
R^2 correlation wouldn’t make sense on a X vs T plot. Its typically used to compare the degree of correlation of two separate variables (i.e. on a scatter plot).

kwik

Norway has already given lots of money during many years to the Soviet’s to put filters on them large factories up in Nickel ….they never used it to filter the smoke anyway….the whole area was black for kilometers after kilometers.
Dont know how it is at the moment…. but back then you could see when you crossed the border to Soviet-land.
Free country; Clean.
Communist land; Dirty.

Steve Goddard

Richard,
The analysis starts in 1989, because that is when the current upwards trend started. The 1970s was cold and had an unusually large amount of snow. Snow cover declined during the 1980s from the 1970s peak.
Winter snow cover has now returned to the record high values.

atmoaggie

Trends aside for the moment, this past winter is reaching for the snowfalls not seen since the winter of 1977-78 (as has been well covered). What do this year and the winter of 1977-78 have in common? An El Nino combined with a near-neutral to negative PDO index. That notable winter was the last time this combination happened.
Just as the causes of the PDO’s behavior is not well understood, I am of the opinion that it’s teleconnections are poorly understood, as well. (no surprise, it is a 60 year cycle and we have measured one half of one cycle via global coverage by satellite…and there is no guarantee that this particular cycle is representative of the norm as variability exists in the cycles themselves)
PDO index by month: http://jisao.washington.edu/pdo/PDO.latest
PDO index history plot here (only through Sept 2009): http://jisao.washington.edu/pdo/
another plot…a little experimental: http://www.esr.org/~gunn/pdo/pdo_fig1.png

kyle

Snowmageddon provides a “teachable moment” to explain the reality of the effects of Global Warming pollution.
Listen to the Earthbeat Radio podcast: http://bit.ly/a7m4n1

Steve Goddard

Leif,
While the trend is slightly upwards, there has been no statistically significant trend in weekly snow cover over the last 20 years. Winter maximums have increased significantly while summer minimums have stayed relatively constant.
http://wattsupwiththat.files.wordpress.com/2010/02/snow_response1.png
It has been claimed repeatedly in the press that snow cover is declining, but the evidence does not support that over the last two decades. A Google search of snow cover decline turns up over one million hits.
What is your point? Do you think that winter snow cover has not been increasing and is not at or near a record maximum?

Matt (08:17:53) :
R^2 correlation wouldn’t make sense on a X vs T plot. Its typically used to compare the degree of correlation of two separate variables (i.e. on a scatter plot).
R^2 value does make sense in evaluating a trend. A trend is just that: a correlation of a variable with time. Remove the connecting lines [which are artificial anyway] and the graph is indeed just a scatter plot.

Steve Goddard (08:30:34) :
While the trend is slightly upwards, there has been no statistically significant trend in weekly snow cover over the last 20 years.
What is your point? Do you think that winter snow cover has not been increasing and is not at or near a record maximum?

My point is that it is a bit silly to open a post with a graph that has no significant trend with the words: “As you can see in the graph below, the overall annual trend since 1989 has been slightly upwards”
And we still do have any explanation why the first 20+ years were left out. If you leave out all the data except the last two years, you’ll get quite a correlation. So what was R^2? You are beginning to sound like Mann who wouldn’t reveal his R^2 either 🙂

MattN

What the hell will R^2 tell you here?

Fredrick Lightfoot

Now Steve, I can see this is going to get interesting.

Steve Goddard

I am completely at a loss as to what some people are disputing.
We have been told over and over again since Hansen spoke to Congress in 1989, that winter snow is declining and that winter storms are moving north.
Clearly that is not happening, quite the opposite.

Richard Telford

Steve Goddard (08:18:41)
There is nothing wrong with that. Provided you make it explicit what you have done, and acknowledge that by selecting the start point, you inflate the risk of a type I error. The post, as it currently reads, is deceptive. I am not implying that this is your intent. Plotting the entire dataset would be a good idea to clarify matters.

I’ve made my own Excel analysis of the data. The R^2 for the graph above is 0.3, and the slope is 87,000 km^2 increase in Winter snow cover per year. But, this is very sensitive to the choice of starting year. 1989 is a cherry-picked minimum, and the current year’s data is not completely in yet. If you plot from the cherry-picked maximum of 1978-2009 you get a decrease of 8,700 km^2 per year and an R^2 of 0.0035.
Using the Rutger’s data from 1974 onward, the slope of the trend is 19,000 km^2 increase per year, on a standard deviation of 1,400,000 km^2 per year, with an R^2 of 0.02, which is, for all practical purposes, flat.

@ Tom P (08:01:37)
Tom P, that doesn’t add anything to the conversation, and is actually insulting.
Reminds of the comments when I used to read RealClimate.

Lonnie Schubert

John Phillips [above] suggests we may be at the beginning of earth’s next glaciation of the northern hemisphere. I see that possibility too. It is overdue, geologically speaking. The short chart (last 20 years of winter snow extent) would fit a logarithmic increase, which is just what would be expected for the beginning of the creep of the ice sheets south. (Lookout Manhattan Island!)
However, as I recall my geology lessons, the northern ice sheet should need to completely disappear so as to provide sufficient extra open water surface to provide sufficient moisture for the extensive increase in snow, to provide the extensive increase in snow cover, which keeps driving the temperature down with increased albedo and all the water phase change, keeping the ice sheets growing south until the earth cools too much to keep the precipitation cycle going.
Of course, there were those making similar statements in the 1970s.
Hopefully it will take centuries (perhaps millennia) to cool enough regardless.
We still have engineers. I suppose I’m not worried.

Tom_R

>> DirkH (08:15:05) :
No interaction between visible light and O2 or N2, otherwise air wouldn’t be transparent for visible light. So visible light that is reflected e.g. by snow will go outwards. There might be refraction by water droplets, so clouds will diffuse visible light. In the absence of clouds, the light reflected by snow (or white roofs, or any part of the surface) will just radiate into space without warming anything significantly. <<
Visible photons are not absorbed by N2 or O2, but they are scattered by collisions, moreso for shorter wavelengths (hence the blue sky). The scattering process has to add some momentum, and thus kinetic energy, to the air molecules.
Hmm, as I write this I realize that the photon changes direction, but doesn't lose energy since the wavelength doesn't change. How is energy conserved when the air molecule gains kinetic energy but the photon energy remains the same?

Here is where you can find lots of Snow Cover data.
http://www.climate4you.com/SnowCover.htm#NH%20seasonal%20snow%20cover%20since%201966
Here, Rutger, is where much of that data comes from.
http://climate.rutgers.edu/snowcover/

Robert

“Earlier changes in summer snow extent were likely due primarily to soot – not CO2.”
If Zender is correct, yes. And what is the CAUSE of all that soot, accord to Zender? From the abstract:
“Applying biomass burning BC emission inventories for a strong (1998) and weak (2001) boreal fire year, we estimate global annual mean BC/snow surface radiative forcing from all sources (fossil fuel, biofuel, and biomass burning) of +0.054 (0.007–0.13) and +0.049 (0.007–0.12) W m−2, respectively. Snow forcing from only fossil fuel + biofuel sources is +0.043 W m−2 (forcing from only fossil fuels is +0.033 W m−2), suggesting that the anthropogenic contribution to total forcing is at least 80%.”
At least 80% of the soot is caused by BURNING FOSSIL AND BIOFUELS. So his theory is very interesting, and I hope it holds up, since it suggests the Arctic ice could rebound much more quickly if we took corrective action. But that corrctive action continues to be drastically reducing burning carbon compounds for energy.

hotrod ( Larry L )

In the 1970’s when worries of “the coming ice age” were all the rage, they were watching the snow extent closely as a leading indicator of possible cooling. The concept was based on the albedo changes, and the snow’s effect on heat storage on the land mass areas.
A reasonably good analogy would be to think of the land mass as a thermal capacitor, charged with thermal energy by an AC signal.
A given parcel of land grows warmer through the summer, then cools during the winter, eventually reaching some thermal equilibrium, where each year on average its temperature oscillates around a uniform temperature. In the northern temperate region this temp is approximately the ground water temperature and in much of the U.S. is about 55 deg F. (12.8 deg C).
The period of the global cooling concerns was also about the time the TAPPS study came out for Nuclear Winter, and one of the results of that were analysis of the effect of albedo changes on this stable thermal equilibrium temperature.
If you get early snows in the fall, and late snows in the spring, the increased albedo at times when the sun’s elevation angle is high would have much more impact on the thermal energy balance than the same snow extent occurring in the dead of winter.
A deep long lasting snow late in the spring would drastically slow the early spring heating (which would slow the entire summers heat storage). If you also had deep long lasting snow early in the fall, that would cut off solar heating of the ground early.
The worst possible situation would be deep long lasting snowfalls early in the fall, and late in the spring and very little snow (thin snow cover) in the depths of the winter. This would minimize heat insulation effects of the snow in the peak cold of the winter while still maintaining high albedo.
In the late 1970’s early 1980’s we had a nearly snow less winter here in Colorado and had major problems with deep freeze lines in the soil, causing all sorts of problems with frozen water lines etc. as the sharp cold temperatures in January and February froze the ground. Construction nearly ground to a halt over the winter as the ground was too hard to dig even with back hoes. A friend of mine spent that winter welding new teeth on backhoe buckets for a local construction company.
Any way back to the snow extent. One of the theories that came out of all this examination of albedo and timing/extent of snow was the theory of the “snow blitz” trigger for entering an ice age. Basically they suggested that a couple short summers due to heavy snows at the right time, could basically cut off summer time heating enough to trigger a plunge in seasonal average temperatures and that global temperatures would follow.
This pattern would have to repeat for several years running and in both hemispheres to trigger a global ice age. The snow blitz theory was one attempt to explain what triggering event pushed the climate over the edge into the actual ice age once the orbital cycles were in the proper phase to support long term glaciation. Some archelogical evidence showed that the changes in flora and fauna at the time of the shift into glacial dominance might happen very quickly (perhaps decades or even a few years). This led to hypothesis’s like the snow blitz hypothesis to explain the sudden change in prevailing weather, that lead to the change in the general climate. On the oceans the same theory applies to ice cover, as its extent late in the fall and late into the spring would strongly effect solar heating of the water beneath the sea ice do to absorption of solar energy. In that case the sea ice switches from acting as an insulator to keep the polar seas warm in the dead of the winter into sun shades reflecting away heating in the early and late part of the local summer seasons.
http://www.masterresource.org/2009/09/the-global-cooling-scare-revisited/
http://news.google.com/newspapers?nid=1346&dat=19750105&id=HI0sAAAAIBAJ&sjid=-_oDAAAAIBAJ&pg=7160,928089
Larry

John F. Hultquist

Caleb (07:47:41) DirkH (08:15:05) ‘sun rays and molecules’
Figure 2 in the following may be helpful:
http://www.wag.caltech.edu/home/jang/genchem/infrared.htm

A C Osborn

I don’t think that a Trend is even necessary, the human eye can see that there is nothing realy going on with the Summer graph.

Robert

Steve, points #1 and 2# are great, but you need a point #3:
3. Because warmer air holds more moisture, it can be too cold for snow. Antarctica, very example, is in many places too cold for snow. Warmer conditions may increase snow, if they make it warmer but not too warm for snow.

ventana

Spring snow cover is still trending downwards.