John Christy says his new study of Sierra Nevada snowfall shows global warming is not the dire threat many make it out to be.
âIn general, it depends on what religion you have,â Christy said when asked about the reaction to his paper. âIf you believe Man is doing horrible things to the planet, then you canât believe this report. If you believe the other way, then this is a chapter in your bible.â
Climate change skeptics have seized on the report published by the peer-reviewed Journal of Hydrometeorology.
James Taylor â" who is not a scientist and is affiliated with the Heartland Institute, which challenges global warming â" penned a blog for Forbes.com that said, âAlarmists were asserting with near unity that global warming was responsible for winters with below average snowfall. Christyâs study shows that as far as the Sierra Nevada mountains are concerned, the alarmists are wrong on both counts â" there is no trend one way or the other.â
Christyâs climatology colleagues say not so fast.
David Pierce said Christy is going beyond the data in his study, which shows steady snowfall since 1878 in the Sierra, and is making conclusions he hasnât proven.
Global warming models predict snowfall will decrease as temperatures rise toward the end of this century, not now, said Pierce, a researcher at the Scripps Institution of Oceanography in La Jolla, Calif., where he studies the effects of climate change on ocean temperatures and water resources â" including snow â" in the western United States.
Pierce takes exception to Christy making such claims in the media instead of in his study, adding this âis unfortunate because peer-review is the process that filters out unsupported personal opinion from what is backed by evidence.â
Study notes
Christyâs study looks at snowfall measurements in the Sierra and goes back further than any previous ones â" requiring him to hand-input more than 26,000 entries from before 1920.
He is director of the Earth System Science Center at the University of Alabama in Huntsville. He grew up in Fresno, Calif., where he watched with fascination as storms built over the Sierra Nevada mountains and learned to estimate snow levels by memorizing ridges and elevations.
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Another hurdle with his Sierra study was that many stations reported âzeroâ snowfall when what they meant was that they didnât record what fell. This required verification of thousands of numbers â" with some of the worst reporting happening in recent decades as people relied on faulty automated systems or thought others were marking snowfall.
Christy found that snowfall in the Sierra â" despite yearly extremes with lots of snow like last year or little snow like this year â" hasnât increased or decreased. To use the studyâs scientific parlance, there have been âno statistically significant trends in their periods of record (up to 133 years) nor in the most recent 50 years.â
Kelly Redmond, a climatologist at Renoâs Desert Research Institute and deputy director of the Western Regional Climate Center, was not surprised by the findings.
âAs a rule, California temperatures have been increasing, but what snow cares about is the temperature when itâs falling,â Redmond said.
Based on DRIâs âclimate trackerâ data, overall temperatures for the Sierra show a trend toward higher temperatures from 1895 to now. But if you look at just winter months â" when the most snow falls â" temperatures have been steady for more than a century.
As long as precipitation also stays steady, and it has, then snowfall would be stable, just as Christy found.
In fact, rising temperatures wonât necessarily have an effect. Imagine an average winter temperature of 10 degrees below freezing â" even a 5-degree rise would still be cold enough to create snow. Itâs even likely in such a scenario snowfall could increase because, as Redmond explains, warmer air can hold more water, so in general more snow will fall at 5 degrees below freezing than at 10 below.
But if more and more winter days have average temperatures above freezing, then precipitation changes from snow to rain.
Such a scenario could be disastrous for California and Northern Nevada. Without the natural storage of a healthy snowpack, everything downstream that counts on water â" trees, wild animals, humans, farms â" is in danger.
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Heated debate
Some scientists say itâs not right for Christy to claim his study contradicts climate predictions.
âFrom a purely scientific perspective, it is bad form for a scientist to publish a paper and then to claim in press releases and in the media that the paper proves something that the paper itself doesnât actually specifically address,â said Michael Ashley, a professor of astrophysics at the University of New South Wales.
Christy says there was no need to include details on climate models predicting decreased Sierra snow because such studies and claims have been widely made.
He gave the example of U.S. Energy Secretary Steven Chu, who said in 2009 that in a worst-case model of global warming, up to 90 percent of the Sierra snowpack could disappear by centuryâs end.
âWeâre looking at a scenario where thereâs no more agriculture in California,â Chu told the Los Angeles Times.
Christy also mentioned a half-dozen published papers that he says back up his claim that climate models show snow shouldâve decreased in the Sierra by now.
A 2008 paper looked at SWE/P, the ratio of water in snow to the amount of overall precipitation, on April 1 in the West and found decreases in this measurement.
Pierce, a co-author, said that if you look at trends in the paper, it not only doesnât show a decrease for the Sierra, it shows that if the Northern and Southern Sierra are combined, the snow-water ratio is steady, just like the snowfall in Christyâs paper.
The other mountain ranges covered in the paper, however, do show a decline, Pierce added.
Another paper cited by Christy is based on a report by Greg McCabe, a climatologist with the U.S. Geological Survey. McCabe wasnât willing to say the paper said what Christy says it does: âI am not sure that the climate models are accurate enough to actually forecast the exact timing of changes.â
Christy also cited a 2004 paper looking at water in snowpacks on April 1, which he says correlates closely with snowfall. He said this report predicts decreases that should be seen by now.
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When contacted, two of that paperâs authors disagreed. Lead author Katharine Hayhoe said Christy was comparing âapples and orangesâ and making a comparison that âis not really valid.â Edwin Maurer, who did models for the paper, said he would be âwaryâ of making Christyâs comparison.
Better models
There arenât any papers looking at projections of Sierra snowfall, as opposed to snowpack, snowmelt or other snow-related measurements. Snowfall predications are what Christy says his study contradicts.
So, for this story, Pierce worked up 16 models using two different data archives, called CMIP-3 and CMIP-5. CMIP-5 is more advanced and takes into account more things, such as the cooling effects of volcanic ash, and its models predict less of a decrease in snowfall than the earlier formulations.
But the CMIP-3 archive wouldâve been the basis of global warming predictions in the past 10 or 15 years that Christy is referring to.
The results were shared with Christy, who said they support his contention that they predict a decrease in snowfall.
âFor the last 50 years, of the eight CMIP-3 models Dave gave you, six have downward trends, one is flat and one is slightly up â" a clear pattern,â he said. âWhen averaged together, there is no doubt they depict a declining amount of snowfall.â
Pierce disagrees. He said that although some models show negative numbers for snowfall over time, they arenât strong enough in that direction to be statistically significant.
The way he framed the results is that seven out of the eight models show no statistically significant trend, meaning 88 percent of the models agree with Christyâs findings that there has been no statistically significant trend in Sierra snowfall.
Redmond says thereâs too much noise â" meaning too many ups and downs in the snowfall measurements â" to get any trend out of the data yet.
âIf these models (run by Pierce) are thought of as opinions coming from science experts and only one out of eight says âI see something,ââ Redmond said, âthen itâs best to come back later when what they see is a little more clear.â
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Although Redmond is sympathetic to Christy and has co-authored a paper with him, he doesnât think Christyâs study contradicts global warming predictions.
âJohnâs study is a data point in the whole discussion,â he said. âI donât think it in and of itself negates the contention that the climate is warming up and should be expected to warm up.
âThereâs still about 90 years left in this century. With 12 percent of the precincts reporting, do we have the whole election in hand? Thereâs still a lot of room for things to happen in the next 88 years.â
Conclusion
If Christy had wanted to raise a red flag to the public, one way wouldâve been to say something like, âHey, I just did this study and it seems to go against what climate models are predicting, so we better do more research to make sure weâre not being led down the wrong path.â
Instead, Christy flat-out stated climate models are wrong and global warming is not dire â" without backing his claims scientifically. Not surprisingly, this raised the hackles of other climate scientists who have a lot invested in the models and think global warming is dire.
Itâs not the way to help us move forward.
Precisely because emotion often clouds our viewpoints, on this topic, we must have dispassionate, peer-reviewed facts â" facts that other experts have tried to tear down and canât â" so that we in the public can make informed choices about how to handle global warming.
If Christy is right that a global disaster isnât waiting at the end of this century, he owes it to all of us to hold up this claim to scientific scrutiny. This is too important of a claim to make untested. If heâs looking for new study topics, hereâs a perfect candidate.
â" Mark Robison is the Reno Gazette-Journalâs data editor and one of its Fact Checker writers.
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