Thursday , February 16, 2012 - 3:01 PM
Snowfall in the Sierra Nevada has remained consistent for 130 years, with no evidence that anything has changed as a result of climate change, according to a study released this week.
The analysis of snowfall data in the Sierra going back to 1878 found no more or less snow overall -- a result that, on the surface, appears to contradict aspects of recent climate-change models.
John Christy, the Alabama state climatologist who authored the study, said the amount of snow in the mountains has not decreased in the past 50 years, a period when greenhouse gases were supposed to have increased the effects of global warming.
The heaping piles of snow that fell in the Sierra last winter and the paltry amounts this year fall within the realm of normal weather variability, he concluded.
"The dramatic claims about snow disappearing in the Sierra just are not verified," said Christy, a climate-change skeptic and director of the Earth System Science Center at the University of Alabama in Huntsville.
Climate experts and water-resources officials were immediately skeptical of the report, pointing out that it doesn't come to a meaningful conclusion and uses data from a ragtag collection of people, many of them amateurs.
Christy's study used snow measurements from railroad officials, loggers, mining companies, hydroelectric utilities, water districts and government organizations going back to 1878. That's when railroad workers began measuring the snowpack's depth near the tracks at Echo Summit using a device similar to a yardstick.
Christy said some of the information will be published in the American Meteorological Society's online Journal of Hydrometeorology.
Christy divided California into 18 regions based on the amount of snow that falls and on the quality of the records for that region, and crunched the numbers. They show no changes in average snowfall over the 130 years and no changes from 1975 to 2000, a period when studies have shown that global temperatures rose. The snow level was consistent even in the Sierra's western slope, where much of California's water supply comes from.
"California has huge year-to-year variations and that's expected to continue," Christy said.
Mike Dettinger, a climatologist and research hydrologist with both the Scripps Institution of Oceanography and the U.S. Geological Survey, said Christy is picking and choosing data while misleading people about what climate-change scientists are actually saying.
For one, he said, snow depth is not as good a measure of the winter weather conditions as water content and density.
The number of inches or feet of snow on the ground can mean a variety of things, he said, depending on if it is fluffy powder or compacted, wet snow.
Recent studies by Scripps scientists have found that over the last 50 years the southern Sierra snowpack has gotten larger while the northern Sierra pack has shrunk. Although they have predicted the overall state snowpack would decrease over time as a result of climate change, nobody has claimed that it has happened yet, Dettinger said.
What's significant in terms of global warming, he said, is the fact that the snowpack has declined over three-quarters of the western United States, an area that includes Montana, Wyoming and New Mexico. Scripps researchers, in coordination with Lawrence Livermore National Laboratory scientists, have concluded that 60 percent of that downward trend is due to greenhouse gases.
"There is a popular conception that the snowpack has declined everywhere, but that is not what the science says," Dettinger said. "What we're saying broadly is that across western North America there have been declines in spring snowpack."
(Peter Fimrite is a San Francisco Chronicle staff writer. Contact him at firstname.lastname@example.org.)
(Distributed by Scripps Howard News Service, www.scrippsnews.com.)
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