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Posted at 12:30 PM ET, 01/13/2011

Does snow cover extent debunk global warming?

By Jason Samenow

Snow cover extent as of 1/13/11. Source: National Operational Hydrologic Remote Sensing Center

Snow on the ground in every state except Florida. Sixty-five percent of the nation covered in snow (down slightly from yesterday's 71% due to melting in the South). Is this evidence to question global warming?

Simply put, no.

A snapshot of snow cover in some part of the world at a given time tells us nothing about the global picture or the long-term trends.

A dataset tracking annual snow cover since the late 1960s over the entire Northern Hemisphere, from Rutgers University's Global Snow Lab, does not show an increasing trend. Rather, it suggests a decline.

Northern Hemisphere snow cover anomalies (departures from average) spanning November 1966-December 2010. Source: Rutgers Global Snow Lab

The record shows there is considerable year-to-year variability in annual snow cover, but snow cover tended to be higher through the mid-1980s compared to the past 15-20 years. This becomes evident by tracking the black line - the moving average - in the graph above.

Snow cover extent declines have been pronounced in spring, whereas the trend in winter and fall has been relatively flat. See the images below for seasonal visuals and look at the black trend line in each of the graphs.

Winter Northern Hemisphere snow extent (1967-2010). Black line is trend line. Source: Rutgers Global Snow Lab

Spring Northern Hemisphere snow extent (1967-2010). Black line is trend line. Source: Rutgers Global Snow Lab

Fall Northern Hemisphere snow extent (1967-2010). Black line is trend line. Source: Rutgers Global Snow Lab

The overall tendency toward decreasing snow cover is not surprising in light of long-term increases in global average temperatures. On Wednesday, both NASA and NOAA announced 2010 had tied 2005 for the warmest year on record.

(Unfortunately, there is not a comparable dataset for the Southern Hemisphere, although there have been some regional studies. Note: the amount of land area in the Southern Hemisphere (SH) is less than the Northern Hemisphere so snow cover changes in the SH would have a relatively small influence on global snow cover.)

By Jason Samenow  | January 13, 2011; 12:30 PM ET
Categories:  Climate Change, Latest, U.S. Weather  
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Next: PM Update: Cold holds, winds diminish


Less snow = :-(
Longer local growing season due to climate change = :-)
Hey, give me lemons & I'll do my best to make lemonade.

Posted by: FIREDRAGON47 | January 13, 2011 12:46 PM | Report abuse

I've read global warming increases the likelihood of violent storms, which in the winter can lead to more snow cover.

1978 is the last time I can recall New England having two blizzards in such close proximity. I only made it as far NE as NYC after the second one, but even there snow piles on the side streets in Manhattan were up to the second story of bldgs.

And when is the last time so much of Dixie had two signficant snows in barely more than two weeks? Might have to go back to March 1960 when there were helicopter food drops to snowbound residents in western NC.

Posted by: JerryFloyd1 | January 13, 2011 1:08 PM | Report abuse

i liked that theory i read here (a week or two ago?) about how the warming arctic might be somehow causing cold air to "drop" out of the arctic onto us? if it brings more snow to falls church, i'm all for it...

how do they measure "snow extent"? i mean that changes everyday, right? is it "permanent" extent (where snow stayed on the ground all season)? maximum extent? average of daily extents?

Posted by: walter-in-fallschurch | January 13, 2011 1:32 PM | Report abuse


Global warming should increase winter the fact snow cover hasn't changed much during winter isn't terribly surprising.

Posted by: Jason-CapitalWeatherGang | January 13, 2011 2:05 PM | Report abuse


Rutgers describes how they measure snow here: About the data. Basically, it's measured via satellite.

Posted by: Jason-CapitalWeatherGang | January 13, 2011 2:10 PM | Report abuse

I feel like a broken record.

It doesnt have to be THAT cold for it to snow. It just has to be cold ENOUGH. Expect more larger east coast storms.

Posted by: DullesARC | January 13, 2011 2:12 PM | Report abuse

I'm curious what the prevailing or consensus view of global warming advocates is on the question of whether the earth can be self-correcting. In other words, I gather that advocates believe the planet will continue to warm up, and don't expect the warming effect to itself trigger a global counter-reaction. Thanks.

Posted by: novajeffc | January 13, 2011 2:12 PM | Report abuse

HAHA, what a twist of fate! Guess where Dr. Robinson his data? This "crude illustration"!:

Posted by: Brian-CapitalWeatherGang | January 13, 2011 2:22 PM | Report abuse


I could write a whole post regarding what goes into creating the maps that Rutgers uses to calculate snow extent. Basically, we have GIS-based program called the Interactive Multi-Sensor Snow and Ice Mapping System (IMS) on which we can pull in pretty much every satellite data source that we have available, visible, microwave, geostationary, polar orbiting, etc. and where we can overlay surface station reports from all over the world. From this an analyst will create a snow and ice overlay layer for the northern hemisphere once a day valid at 00z at a resolution of 4 km (way better than the automated microwave products). This is then fed into the numerical models and shipped out to customers such as rutgers for climate research. I'm also developing a Sea Ice maximum and minimum product (available on the webpage) that we run from the maximum (March) to the minimum (September) to chart seasonal sea ice loss in the Arctic.

Posted by: Brian-CapitalWeatherGang | January 13, 2011 2:34 PM | Report abuse

"The overall tendency toward decreasing snow cover is not surprising in light of long-term increases in global average temperatures."

I feel like this statement should be limited to those months when snowfall is temperature limited: eg, I'd expect later first snowfall and earlier last snowfall for any given region, and perhaps less snowcover in southern regions that rarely reach freezing temperatures. However, during the depths of the winter, the increased ability of warmer air to hold moisture should mean that as long as the temperature is still freezing, warmer = more snow. Does modeling indicate which effect would be expected to be larger on the annual average?

(this is kind of like the greenland ice sheet argument: increased snowfall in the interior was expected to balance out increase melt at the edges for small warming. Of course, observations have since indicated otherwise)


Posted by: marcusmarcus | January 13, 2011 2:48 PM | Report abuse

thanks guys.

what i'm wondering is how do they take all that data and come up with a value for a given year on those fall, winter and spring charts? i.e., is that 2010 value of ~47.5M for winter the average of each of the daily values for winter?

Posted by: walter-in-fallschurch | January 13, 2011 3:14 PM | Report abuse


Great point. I didn't go into the seasonal details and modeling... but the dramatic spring decline is a pretty strong global warming signal whereas the fact winter is flat is not surprising given increases in precip which probably negate melting from warmer temps at lower latitudes. Would be interesting to look at how models handle the balance.

Posted by: Jason-CapitalWeatherGang | January 13, 2011 3:27 PM | Report abuse

i think if the earth is warming its doing so as a natural cycle. i dont believe at all that man is causing the earth to warm or cool, we have no power to do that, nature is more powerful than man.

i just dont think there is any way to prove man made global warming exists, our recors of average global temps just dont go back far enough to be sure that the earth isnt going through its natural cooling/warming cycle.

the biggest mind blower for me is that the global warming believers blame everything on global warming. when its too hot, they blame global warming. when its too cold they blame global warming. when theres alot of snow they blame global warming, when theres no snow again, its global warming.

i just dont believe that we bumans are causing any of this, we arent. capable of it. extreme winters/summers along with extreme storms have always haPpened throughout history. huge blizzards and long xroughts are nothing new. and most importantly, volcanoes throw out more hazardous chemicals into the air than my car could do in a lifetime.

lets cap the volcanoes aNd put sun resistant blankets over all the ice on earth ;)

Posted by: KRUZ | January 13, 2011 3:41 PM | Report abuse

When will the PM Update be posted?

Posted by: BobMiller2 | January 13, 2011 3:50 PM | Report abuse

How much does a volcano put out compared to hundreds of millions of cars? I would guess the cars' output would outdo the volcano.

As for man's ability to change the environment, man-made freons did a job on the ozone layer. We stopped producing nearly all freons and the ozone layer started to heal. We have also managed to make a few species extinct.

It is a fact that carbon dioxide absorbs infrared radiation. By increasing carbon dioxide, more IR is trapped and the earth will be warmer. If the atmosphere is warmer, it will hold more water vapor and trap more IR. How much? You need to do the math and many scientists have tried. We know the equations that govern the atmosphere and they have been integrated in climate models. The results from climate models suggest that the warming we have seen in the last hundred years can be explained by increased carbon dioxide. Are the climate models complete and without problems? Absolutely not. Are they good enough to suggest explanations for the observed warming? I and many other scientists think so.

Unfortunately mankind is powerful enough to change the climate.

Posted by: Dadmeister | January 13, 2011 3:59 PM | Report abuse

"i dont believe at all that man is causing the earth to warm or cool, we have no power to do that, nature is more powerful than man."

#76 it's not us

#84 it's a natural cycle

"most importantly, volcanoes throw out more hazardous chemicals into the air than my car could do in a lifetime."

#60 volcanos emit more

Posted by: walter-in-fallschurch | January 13, 2011 4:04 PM | Report abuse

you say, "i and many other scientists think so."

are you a scientist? what kind?

Posted by: walter-in-fallschurch | January 13, 2011 4:14 PM | Report abuse

Kruz -> So your suggesting a cycle of over 650K years? Epica and Vostok cores show no CO2 concentrations as high as we have now going back that far, not even close to the current levels. CO2 is incontestably a greenhouse gas... Are you suggesting a solar cause? Even that would not connect to a 650K+ frequency, I can't think of anything that would.

As far as the multiple incarnations of warming, it was for that reason that the term climate change came into use because people weren't catching on that global energy retention did not mean uniform warming. Global warming is not necessarily local warming.

Finally, Venus.

Posted by: miglewis | January 13, 2011 4:55 PM | Report abuse

If we all take off our cotton "yes AGW" and wool "no AGW" hats for a moment, I think we would all agree that snowfall will fluctuate naturally, some years or decades will be snowier than others. That is the way nature works. The question is then is there a trend over time (that won't reverse) corresponding to AGW? My answer (after putting my nice warm hat back on) is there is no irreversible trend towards less snowfall.

IOW, there will likely be more snow again like there was in the 60's and 70's. One possible explanation is that AO is going strongly negative, strongest since 1977. On the ocean cycles, AMO may (too soon to tell) also start to look like the 70's. PDO dropped back to 70's values starting in the early 2000's (with no repeat of 70's weather). The other problem with comparing anything with the 70's is that the 70's had a lot a variation (had more snow and less snow at various times).

Low solar activity seems to drive negative AO (through higher GCR and lower UV and probably other effects). Lower solar activity has less clear link with the oceanic cycles, PDO and AMO. And all of those will be affected to some extent by AGW although I would say that ice-free Arctic is not a direct driver of AO, but may dictate some of the jet stream patterns in a negative AO situation. That could mean more snow in the middle of ocean where it isn't measured.

Posted by: eric654 | January 13, 2011 5:01 PM | Report abuse

KRUZ - While I completely understand what you're trying to say and can't argue that global warming may very well just be a natural cycle (more likely actually), I do find it odd that you're arguing, oddly in a way, that man isn't a part of nature...almost as if what we do has no impact at all...when everything else in nature does. When any population of a species rapidly grows over a short period of time, and that species is using massive amounts of energy in order to live and grow even further (man, or whatever), odds are pretty good it has at least a minor impact on nature, don't you think?
Although, I think people arguing man-made climate change also completely miss the natural change side too…as if everything that happens is a direct impact of man, also an odd argument.

Posted by: parksndc | January 13, 2011 6:51 PM | Report abuse

parksndc, man-made global warming is not an *argument*, it is a scientific conclusion from the *evidence*.

Posted by: imback | January 13, 2011 9:31 PM | Report abuse


What kind of a scientist am I? I've studied and worked in atmospheric science/meteorology for 36.5 years. Currently I'm involved in evaluating numerical weather prediction. I evaluate weather models, not climate models, but they are close relatives to each other. Weather models have it easy, they are tested and evaluated every day on their forecasts, making it easier to find their flaws and try to correct them.

By the way, I do find some people try to attribute every weather event to global warming. I believe the correct answer to such questions is "We don't know. It's very difficult to say what part of day to day weather events is due to climate change and what is due to natural variability that would have occurred without greenhouse gases increasing."

One problem is the failure especially in the mass media to distinguish between a hypothesis and a theory. That the earth is warming is a scientific fact. That much of the warming is due to anthropogenic influences, of which carbon dioxide is the strongest, is a well-established theory, the best explanation of the facts that we have. That a warmer Arctic and declining Arctic sea-ice caused more sevcere winters over the eastern US and Europe is a hypothesis, not thoroughly tested in my humble opinion.

Posted by: Dadmeister | January 14, 2011 9:05 AM | Report abuse

Could climate change be a natural phenomena caused independently of man, absolutely. Just like the fact that I am gaining weight could be a natural phenomena independent of my eating habits. However, it is more than likely it is the McDonalds I shove down my throat every night for dinner. Obviously when dealing with climate cycles which last thousands of years or longer it is impossible to say definitively but the idea that all of the pollutants humans put into the atmosphere have zero effect is beyond the realm of skepticism.

Posted by: jbernard703 | January 14, 2011 11:20 AM | Report abuse

thanks for the info. so you ARE one of those people qualified to give a scientific "opinions" on weather/climate-type issues.

i agree about your distinctions btwn fact, theory and hypothesis. nonetheless, the "AGW means more snow for falls church" hypothesis is one i'd love to see verified over time...

Posted by: walter-in-fallschurch | January 14, 2011 12:31 PM | Report abuse


We're talking about the combined chemical compound output of nearly 7 billion on earth would you know that has no effect on our climate? The best-case scenario is that it doesn't; in that case any efforts to mitigate the effects are for naught other than the benefits conferred to us for having a cleaner environment (which are considerable). Yes, we'll have spent money making conversions and such, but in the meantime we'll have created jobs for making those conversions. The worst-case scenario is that we DO have a considerable impact on the climate; in that case to do nothing is to speed our demise.

Posted by: markf40 | January 15, 2011 6:35 PM | Report abuse

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