A new report says snowfall in the Sierra hasn’t shrunk, but not everyone’s buying it
There are good years and there are bad years, but overall, snowfall in the Sierra hasn’t declined in the past century. That’s according to a new study by University of Alabama climatologist John Christy (who, it’s worth noting, has come under fire as a climate change denier).
The San Francisco Chronicle had a story about the report, “Searching for information in 133 years of California snowfall observations,” (link is to the abstract; full article is behind a pay wall) in today’s paper:
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.
Roger Bales, a professor of engineering at UC Merced and director of its Sierra Nevada Research Institute, said this study can’t be used to draw conclusions about climate change.
“(Christy) may have done some appropriate statistical analysis, but the conclusions are stressed beyond what the data will bare. It’s not surprising he didn’t find a trend because he lumped everything together.”
Bales said to detect a change in precipitation patterns from snow to rain, which is an indicator of climate change, the details of the data at specific elevations would be more valuable than all the numbers combined.
The Chronicle also quoted U.S. Geological Survey climatologist Mike Dettinger, who said that water content and density of snow are better measures than snow depth.
Kelly Redmond, a climatologist at the University of Nevada’s Desert Research Institute said he was slightly surprised to see the report, but not floored by it.
“It’s quite natural to say if it’s warming up we’ll see less snow, but in some places because of higher temperatures, we could see more,” he told me. “There’s that famous quote by René Dubos, ‘Trends are not destiny.’ This is a study of what it’s been up to this point. But I’m hesitant to say if it’s been this way, it’s going to stay this way.”
John Christy got in touch, and I asked him to respond to some of the points in this post. I’m copying his response in here.
Snow Water Equivalent (SWE): my recent paper directly addressed that issue and found snowfall a very good proxy for SWE. SWE is a valuable measure of one thing (amount of liquid water in the snowpack on a particular date, which misses the impact of later snowfalls). SWE is very useful for its purposes, but only a few measurements go back to around 1930. Snowfall is a different metric (my paper) and goes back another 50 years (thanks to a lot of effort on my part) and so has the high added value of length-of-record as well as a metric of great value to define snow amounts as they fall (for recreation, snow clearing, snow-dependent ecology as well as runoff).
The rate of change of snowfall has been modeled to have already shown decreases (in the models). I addressed issues like temperature (Christy et al. 2006) and runoff/precipitation (Christy and Hnilo 2010 attached) … no changes have been found. Thus, models are not doing well in showing what mother nature is doing. It’s always a nice corner to run to by saying “our predictions can’t be tested because they apply only to the future” — the infamous unfalsifiable hypothesis. I test model results for the time over which we have both observations and model results. (My main work is dealing with global temperatures from satellites where it is more straightforward to show model vs. observation disagreement.)
One critical part of the paper was the handling of “missings as zeros,” where non-reports (i.e. missing) had been filled in with zeros since 1970 by someone down the line for many stations. I had to eliminate as many of these as possible — a very tedious process.
I looked at the elevation dependence in the So. Sierra in the last paper. Note that in the past 60 years, most sites showed positive trends, with no dependence on elevation.
Regarding the Calif. Water Report — the blog commenter was comparing very different apples and oranges: the time frame is different in two ways and the quantity itself is very different. In Fig. 2-13 the quantity is only Apr-Jul runoff for the Sacramento Basin only, not total annual runoff of all of the Sierra. The annual runoff (Fig. 2-14 lower and Fig. 2-16 lower) shows precisely what I found — no trend. The time periods are different too — mine go back 30 years more. It looks to me like California will have roughly the same amount of water it has had for the last 100 years — but I know the demand for water is always rising.