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USGS-led study finds that recent unusual snowpack declines in the Rockies may signal a fundamental shift from precipitation to temperature as dominant influence

A new study led by the US Geological Survey (USGS) suggests that snowpack declines in the Rocky Mountains over the last 30 years are unusual compared to the past few centuries. The paper is published in Science.

Over the past millennium, late-20th century snowpack reductions are almost unprecedented in magnitude across the northern Rocky Mountains, and in their north-south synchrony across the cordillera. Both the snowpack declines and their synchrony result from unparalleled springtime warming due to positive reinforcement of the anthropogenic warming by decadal variability.

...Together these events may signal a fundamental shift from precipitation to temperature as the dominant influence on snowpack in the North American Cordillera, with significant consequences for regional water supplies.

—Pederson et al.

Runoff from winter snowpack accounts for 60% to 80% of the annual water supply for more than 70 million people living in the western United States.

USGS scientists, with partners at the Universities of Arizona, Washington, Wyoming, and Western Ontario, led the study that evaluated the recent declines using snowpack reconstructions from 66 tree-ring chronologies, looking back 500 to more than 1,000 years. The network of sites was chosen strategically to characterize the range of natural snowpack variability over the long term, and from north to south in the Rocky Mountains.

With a few exceptions (the mid-14th and early 15th centuries), the snowpack reconstructions show that the northern Rocky Mountains experience large snowpacks when the southern Rockies experience meager ones, and vice versa. Since the 1980s, however, there were simultaneous declines along the entire length of the Rocky Mountains, and unusually severe declines in the north.

Over most of the 20th century, and especially since the 1980s, the northern Rockies have borne the brunt of the snowpack losses. Most of the land and snow in the northern Rockies sits at lower and warmer elevations than the southern Rockies, making the snowpack more sensitive to seemingly small increases in temperature. Also, winter storm tracks were displaced to the south in the early 20th century and post-1980s. Forest fires were larger, more frequent and harder to fight, while Glacier National Park lost 125 of its 150 glaciers.

—USGS scientist Gregory Pederson, lead author

USGS scientist and co-author Julio Betancourt said that the difference in snowpack along the north and south changed in the 1980s, as the unprecedented warming in the springtime began to overwhelm the precipitation effect, causing snowpack to decline simultaneously in the north and south.

Throughout the West, springtime tends to be warmer during El Niño than La Niña years, but the warming prior to the 1980s was usually not enough to offset the strong influence of precipitation on snowpack.

—Julio Betancourt

The La Niña episode this year is an example with lots of snow in the north while severe drought afflicts the south. But, in the north, this year’s gains are only a small blip on a century-long snowpack decline.

In the West, the average position of the winter storm tracks tend to fluctuate north and south around a latitudinal line connecting Denver, Salt Lake City and Sacramento. In El Niño years, winter storms track south of that line, while in La Niña years, they track to the north.

This study supports research by others estimating that between 30–60% of the declines in the late 20th century are likely due to greenhouse gas emissions. The remaining part of the trend can be attributed to natural decadal variability in the ocean and atmosphere, which is making springtime temperatures that much warmer.


  • Gregory T. Pederson, Stephen T. Gray, Connie A. Woodhouse, Julio L. Betancourt, Daniel B. Fagre, Jeremy S. Littell, Emma Watson, Brian H. Luckman, and Lisa J. Graumlich (2011) The Unusual Nature of Recent Snowpack Declines in the North American Cordillera. Science doi: 10.1126/science.1201570



Oh my... another bogus "study" from the unwilling to accept fact "scientists" in service of AGW theory. How easy is it to prove the bogussness?? Just view the hard data actually referenced in the Science paper...

The data are April snow water equivalent standard deviations or SWE. The paper claims:

"Over the past millennium, late-20th century snowpack reductions are almost unprecedented in magnitude across the northern Rocky Mountains..."

But when you look at the actual data from 1935 - 2006 (used by USGS Pederson) the April SWE average (plus or minus 1) is steady with snowpack increases in the last two years.


Looking at the southern cordillera (Colorado) and checking the NRCS SNOTEL Colorado data reveals no change in average SWE from 1935 - 2009:


THX W.Eschenbach & WUWT for truth vigilance. These are desperate times for the remnants of AGW. It is embarrassing to claim these papers pass any kind of "peer review."


Trees can tell a relevant history over 1000+ years. Deniers will never believe it. Loosing 125 out of 150 glaciers is peanuts. Others will grow as the West gets dryer and hotter?


What is probably needed at this point is some serious attention to treating collective misanthropy. This is an unfortunate condition based on old forms of prejudice and racism. Misanthropy today expresses itself in a collective conscious consumed with blaming an entire species of beings for global faults.

The odd element of this condition is most of the faults are products of the misanthropist's imagination. Tolerance, acceptance and vigilance against prejudice are all-important corrections.


So tell us, Reel... what do Arizona and the rest do for water in the summer, when their "snow equivalents" fall as rain and have run off by mid-May?


"Hydrologists, meanwhile, are cheering what they say will be a huge increase in water reservoir storage for tens of millions of people across the West. Lake Mead and Lake Powell, two huge dammed reservoirs on the Colorado River battered in recent years by drought, are projected to get 1.5 trillion gallons of new water between them from the mammoth melt. " May, 2011


I found this amazing resource... the internet!!


errata: in the earlier "bogussness" is misspelled. Should be bogusness...

Aaron Turpen

Not sure what Rockies they were "surveying," but Colorado, Utah, and Montana are expecting FLOODING this year due to heavy snowpack melting.

Someone tell these global warming scientists that we're in the Holocene and have been warming for 10,000 years.

Aaron Turpen

Engineer-Poet: they realize that they shouldn't have built their houses in the damn desert and expected to have a green lawn and big trees. That's what.




How long will deniers take to realize that climate is changing and that we are partially responsible?


What makes you think they don't realize it?

When people deny something that has as much evidence behind it as AGW does the reason has to be more than not realizing it. They stay in denial because of dogma, the backfire effect, lack of mental plasticity (we all lose that with age), or ego.


Crickets... and mosquitoes.


Yes, flooding during the all-at-once spring melt, Aaron.

Is Lake Mead going to be full again, though? Dream on.


750 billion gallons will swell Lake Mead nicely.


I think Lake Mead is currently only 41% full and the last time it was this low it took 19 years to refill.


According to the Bureau of Reclamation Upper Colorado Region Water Operations:

"The unregulated inflow forecast for Lake Powell over the next 3 months based on the May [2011] preliminary Water Supply forecast is as follows: June-6,100 kaf (198% of average); July-3,300 kaf (212% of average); August-950 kaf (155% of average). This forecast was last updated on June 3, 2011. Incorporating these new forecasts the most probable Lake Powell unregulated inflow volume projection for water year 2011 is 16.7 maf (138% of average).

Only 5 of 47 years since the closure of Glen Canyon Dam have had unregulated inflow volumes greater than what is projected for this year. Natural variation - Earth's climate regulator for the last 4B years - continues to function normally.

Stan Peterson


Since I live in Phoenix, the hottest city in the World, we are celebrating the coolest summer in recorded Phoenix history. It is mid-June and we have had but a single day over 100 degrees, (in February!) when we ordinarily would have had two steady months of such temperatures. Meanwhile we can enjoy our air conditionisng powered by cleanly fracturing actinide nuclei, and sip our cool Magaritas.

At the same time, our "silver necklace" of reservoirs are full to overflowing. The two mammoth damms and reservoirs on the Colorado, that we don't rely on for water, but could, the 1930s era Lake Mead and the 1960e era Lake Powell, are rapidly filling from the mammoth snow melt that ordinarily would be about finished, but has just begun to feed them. Lake Powell will be over 80% full and is dumping water at amximum flow to replenish Lake Mead. Both had fallen to mid levels in the previous ten year drought, but the water that might have fallen on drought stricken Texas and Oklahoma has fallen as snow on the Rockies this year. Most of the Colorado drainage has snow accumulation of 200-250% above normal.

If it had not been for the lower levels of the reservoirs, to absorb this snow melt, we would be facing floods similar to the flooding that occured here in the 1980s, and 1960s before that, and is affecting the Missisippi River Valley now.

Proving once again that there is no world ending disaster, just normal fluctuations. We also know that the Hohokam Indians had to leave Arizona in the 700-800s due to a prolongued droght, before this "millenial" USGS study.

Global Warming Cassandras can't have it both ways, although they do try. A warmer world would also be a wetter world, with more evaporation and consequently more rainfall.

I should be much more inclined to observe the USGS revised estimates of recoverable oil in the Williston formation. When the USGS annaounces that formation contains more recoverable Oil than in Saudi Aarabia, using current technology, I would want to take notice. OTOH, teh US demand for Oil has been declining now for going on 9 years, according to the IEA, so it won't be long before we don't care.


What we confirm in this story is USGS Mr. Pederson et al, Science, and peer reviewer's lack of ability to do rigorous science. Many of the paper's statements bear zero support from the underlying data. Were it not for the rigorous work of third parties, many inured to believe in "official" institutions like USGS, and Science "The World's Leading Journal of Original Scientific Research" - would find this "paper" disturbing.

But as we see from the above dialog - neither Pederson et al, Science and peer reviewers or the USGS is rigorous enough to do the science. This casts a lengthening shadow across the remnant of the AGW campaign, its Science journal, peer reviewers and the USGS. In one fell swoop the integrity of all these players is irreparably tarnished. THIS is why all major industrial nations have rejected an extension of Kyoto. Lack of Integrity. Once lost, it's hard to recover.

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