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:
- Snow falls in the winter, in places where it is cold. Snow does not generally fall in the summer, because it is too warm.
- 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.
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.
Richard (18:19:39) :
I let you off when you made a blunder re black bodies, also about CO2 freezing out of the atmosphere.
It is nice that you let me off all my blunders. The one about black bodies I don’t recall. Refresh my memory [use email if needed].
But you are getting insufferable. If you do not have a point keep quiet, just let it go.
Well, I think I do have a point, namely that one does not start out a topic by claiming there is a clear trend. when there isn’t. R^2 is a perfectly valid method to gauge this as I have tried to demonstrate. Now, I’m willing to ‘let it go’ as it is clear to everybody [without my insistence] that there is no significant trend in the first Figure and that by judicious cherry picking one can claim a [barely] significant increase.
[snip – nice try “thefordprefect” – you are no longer welcome here when you do shape shifting, pick a name preferably your real one, and stick with it, otherwise bugger off]
Steve – Zender did NOT claim that 80% of the soot was due to burning of fossil and biofuels. Read it more carefully
“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%.”
If I read this right this is saying that if you could somehow eliminate the soot due to biomass burning (forest fires and the like), then the remaining carbon generated by fuel burning would cause 80% of the warming. But that isn’t the same as saying that 80% of the soot is due to these sources as the warming effect is non-linear. In other words snow only has to be slightly dirty to cause significant warning and making it twice as dirty probably wont double the effect.
The non-linearity makes the way in which the results are stated deceptive. I suspect that if you analysed the warming contribution of soot from biomass burning in the same way you would find that it too could be said to be `responsible for 80% of the warming’ – maybe more! If so then that would mean cutting all the soot contribution from fuels would only diminish the warming by 20%.
He has presented his results in a rather strange way which I don’t think is very informative. What you would want to know is the marginal impact of mans contribution to the underlying situation, and that isn’t the number he’s chosen to give us.
Dude (18:46:18) :
It is not cherry picking to say that since 1989, snow extent has been increasing.
It is clear that for a climate trend, one or even two years more or less shouldn’t matter. So what is missing is a sensitivity analysis. What difference in R^2 [which is a convenient and valid measure] does it make to start in 1988, 1989, or 1990 and to end in 2009, 2008, or 2006. For a robust signal these small changes shouldn’t matter much. Yet no such analysis was made. The resistance one feels about this may be telling. Of course, I could make that analysis myself, but it really behooves Steve to make it.
Steve Goddard (18:46:03) :
Ah, you found something.
So they say the models do a lousy job with snow cover, they don’t show any (model) trend over the 20th C, but a decreasing trend over the 21st C.
You should also discuss this one (Brown, 2009), which looks to be a newer and more detailed study.
http://ams.allenpress.com/archive/1520-0442/22/8/pdf/i1520-0442-22-8-2124.pdf
As well as the observations, as discussed in Changnon et al, and whatever all the IPCC AR4 had to say about the topic (both observations and projections).
You wouldn’t want to be accused of cherry-picking by not giving the whole context of the literature, after all.
Dude (18:46:18) :
“A second-order polynomial fit would likely result in a higher R^2 value.”
The game is not to increase your R^2 by increasing the order of the polynomial. That’s generally a horrible idea.
Steve Goddard (18:46:03) :
Why are all these models unable to show any increase in snow, decrease in temps, increase in rainfall, etc?
I am wanting to call the computer banks they use Deep Gloom.
davidmhoffer (19:25:41) :
“A photon has momentum so can give you a kick = increase your kinetic energy”
no Leif… you have photons confused withy photon TORPEDOES. They haven’t been invented yet.
The energy and momentum of a photon are related by E = pc, where p is the magnitude of the momentum vector p. The momentum p points in the direction of the photon’s propagation and has a magnitude of p = h/L, where h is Planck’s constant and L is the wave length. So, photons do have momentum and can give you a kick and increase your kinetic energy.
Richard (18:19:39) :
And I do not think you understand the meaning of R^2 for the trendline in this case. Basically it would mean how well does your trendline fit the data
No, that is not what R^2 tells you. It tells you how much of the variation of the data can be explained by a [linear] trend. So, if R^2 is 0.03, it means that 97% of the variation of the data is not due to the trend. By smoothing the data, you increase R^2, but you also decrease the significance as you have fewer independent data points. In the extreme you can form the average of the first half of the data and of the last half. R^2 for those two average points is 1, but the significance is 0.
Carot Eater and Stephen Goddard,
Please note that this June 2009 report indicates that the North East will experience Less Snow due to global warming.
It seems to me that we can find any position we want in these junk government reports except Science:
“June 2009
Members of Congress:
On behalf of the National Science and Technology Council, the U.S. Global Change Research Program is pleased to
transmit to the President and the Congress this state of knowledge report: “Global Climate Change Impacts in the United
States.” This report summarizes the science of climate change and the impacts of climate change on the United States,
now and in the future.”
Global Climate Change IMpacts page 107
“Since 1970, the annual average temperature in the Northeast has
increased by 2°F, with winter temperatures rising twice this much.150
Warming has resulted in many other climate-related changes,
including:
More frequent days with t • emperatures above 90°F
• A longer growing season
• Increased heavy precipitation
• Less winter precipitation falling as snow and more as rain
• Reduced snowpack
• Earlier breakup of winter ice on lakes and rivers
• Earlier spring snowmelt resulting in earlier peak river flows
• Rising sea surface temperatures and sea level”
Also this seems to contradict recent claims by the NYT and others who claimed that scientists predicted the increased snow in the North East we recently experienced.
Help!!!
Jay,
It is fairly obvious from your comments that you didn’t bother to read the article.
I fitted the equation to the data provided.
snow=25,320 + 22,303*SIN[-5.29*2*PHI/(week of year)}
then looked at residuals.
If anyone can see a pattern in these residuals, then he or she has been smoking too much pot!
It is quite clear that climate is neither linear nor a second order polynomial, given that the oceans are neither evaporated nor frozen after billions of years – which would be the necessary consequence.
People can argue endlessly about lies, damn lies and statistics, but sometimes they just need to trust their own eyes.
http://wattsupwiththat.files.wordpress.com/2010/02/dec-feb_snow_ext.png
Starting in 2001, 8 out of 10 years are above 45 million km2. Prior to that, 8 out of 11 years were below 45 million km2. The current year is the second highest on record. Enough with the statistics games, please.
I think the point of the topic was the lack of the CLAIMED negative trend no? I see no negative trend. I think I got the point. I think we could use more common sense in our scientists, maybe there should be a new collegiate prerequisites for BAs or at least PHDs as a minimum. CommonSense Logic101, shortly to be followed by contortionist logic1A, and for the undergraduate requirement…the forest through the trees1B!.
Steve Goddard (20:47:37) :
“just need to trust their own eyes.”
For them to do that, you need to show the entire data set. You can start your trend at 1989 if you really want to, but show the entire data set so people can judge the thing in context – are these trends, or just noise?
Just like with temperature: you could draw a trendline in global temperature up from 1996 to 1998, and then another one down from 1998 to 2000. They’d be pretty impressively steep lines, but would it mean anything?
Ric Werme (12:12:08) :
Steve Goddard (10:20:59) :
> R^2 on the winter graph since 1989 is 0.298514013
9 significant figures? Careful – Leif will start teaching you about significant digits and error bars.
NO THAT IS MY JOB!
carrot,
We have been bombarded with disappearing winter snow stories for years, and if you have been paying attention you should know that.
A CU professor predicted the demise of Colorado skiing in the middle of a record snow year two years ago. The Met Office predicted the demise of snow in England 10 years ago. RFK predicted the demise of snow in Washington DC two years ago. I just pointed you to an article which showed all IPCC GCMs predicting the demise of winter snow.
carrot,
The upwards trend started in 1989. Prior to that there was a downwards trend. If I am showing a graph of the most recent upwards trend, why would I include years that aren’t part of that trend?
If I said “it warmed up 15 degrees between 6AM and 3PM” is that something you would dispute because I didn’t mention the downwards trend prior to 6AM?
Obviously every upwards trend is preceded by a downwards trend. That is a fundamental principle of nature.
Typo. Apologies to all. Should be:
snow=25320 + 22303*SIN[-5.29 + 2*PHI*(week of year)/52]
This is just a curve that symmetrically mimics the earth about the sun. You can get a better fit with extra frequencies, but that just makes it hard to understand and nothing meaningful changes.
I don’t know how to paste the chart of residuals into these comments, but it is easy enough to generate in excel. If you look at the entire period from 1966 there is just no visual pattern of structual change. Sometimes the residuals are bigger sometimes smaller. On the winter side they are smallest around 1989, and largest around 1977-78 and the last couple of years.
Some years there is more so, some less. The year to year variation is entirely within statistical (and visual) norms.
ET,
Bingo! The climate models and forecasts were wrong.
Don Shaw (20:27:13) :
Good find. Keep digging, people. Context is important here: was everybody saying the same thing? Or are the predictions a contradictory and confused mixture? One complication:
“• Increased heavy precipitation
• Less winter precipitation falling as snow and more as rain”
If you combine these two, you could still on net get more snow…
I honestly had no idea what the predictions/statements were on this matter, but I can easily imagine its something the climate models would have trouble with. It’s known that regional precipitation projections need some improvement.
“Also this seems to contradict recent claims by the NYT and others who claimed that scientists predicted the increased snow in the North East we recently experienced.”
First, it’s simply incorrect for anybody to say they used understanding of climate to predict one freak winter. Weather is weather, climate is climate. If they said, “x is consistent with expectations”, that’s fine. Did the articles you read cite any papers? That could add to the pile. I think the Changnon paper shows some sort of increased snowfall trend for the US northeast, though I don’t know if it was significant.
That’s the other problem here – One freak snow season doesn’t prove or disprove any climate projection. And given the high variability in snow data, Goddard’s trend will continue to be questioned.
Well, because I love numbers, I took a look at the snow area figures. I subtracted the weekly average from weekly data to give anomalies. I expressed them as a percentage of NH average snow cover. Here is that graph:
A few comments, in no particular order:
1. As someone mentioned above, the PDO is important in this graph. The PDO went from cool to warm in about 1976, as can be seen in the snow area anomaly.
2. From about 1976 to about 1990, snow area was decreasing slightly.
3. Since 1990, it has increased slightly.
4. Changes over the entire period are about ±5%. By eyeball, none of them look statistically significant.
5. We’re about where we were in 1982.
6. There has been basically no change since 1995.
Now, perhaps there is a signal of a dangerously warming earth in there, but I don’t see it. And perhaps there is a signal of increasing soot melting the snow in there, but I don’t see it.
The change in albedo due to decreased snow coverage is supposed to be a strong positive feedback in the global thermal balance … I don’t see that either.
My conclusion? Either:
a) The land temperature records are badly corrupted, by some unknown combination of UHI, bad station siting, landuse/landcover changes, and nefarious meddling, or
b) Slight changes in temperature don’t change the snow area much. Increasing warmth theoretically increases both snow melt and precipitation, so they may basically offset each other, or
c) Both.
w.
Yeah Willis! Cutting to the chase as always. Now we have some clarity on the question of the shrinking or swelling winter snow extent, no so-called ‘cherry picking’ of dates involved.
“People can argue endlessly about lies, damn lies and statistics, but sometimes they just need to trust their own eyes.
http://wattsupwiththat.files.wordpress.com/2010/02/dec-feb_snow_ext.png
Starting in 2001, 8 out of 10 years are above 45 million km2. Prior to that, 8 out of 11 years were below 45 million km2. The current year is the second highest on record. Enough with the statistics games, please.”
Steve, the site that is your source for this information directly contradicts some of the things you are taking from their data. There is a strong negative trend in both summer and spring snow extent. In 2008, they report, the snow extent was: “1.1 million sq. km less than the 39-year average and ranks 2008 as having the 4th least extensive cover on record…””
It seems as though you are having trouble taking your own advice, and looking at what it right in front of your eyes.
One thing that no one has mentioned would be to compute the area under the curves from minimum to minimum for each year. The time x area should give an interesting look at how much the albedo changes. Any trend in peak levels or minimum levels strike me as being less valuable than the product of the time and the total snow surface available to reflect light.
A cycle with a tall but relatively sharp peak might have less actual effective change in albedo than a shorter but fatter cycle, as the latter would have snow present for a longer period of time.
If you really wanted to get fancy you could compute the days of sunlight for each day of the cycle and also compensate for the changing length of days. A given square area of snow during late December would reflect significantly less energy than the same area during March or April due to the longer day.
Larry