Spurious Warming Trends In The American West

By Paul Homewood  

 

SNOTEL Network

 http://www.wcc.nrcs.usda.gov/snow/

 

WUWT ran a post in January about a warming bias in the SNOTEL station network.

 

From the “temperature bias only goes one way department” and the University of Montana:

Mountain system artificially inflates temperature increases at higher elevations

MISSOULA – In a recent study, University of Montana and Montana Climate Office researcher Jared Oyler found that while the western U.S. has warmed, recently observed warming in the mountains of the western U.S. likely is not as large as previously supposed.

His results, published Jan. 9 in the journal Geophysical Research Letters, show that sensor changes have significantly biased temperature observations from the Snowpack Telemetry (SNOTEL) station network.

More than 700 SNOTEL sites monitor temperature and snowpack across the mountainous western U.S. SNOTEL provides critical data for water supply forecasts. Researchers often use SNOTEL data to study mountain climate trends and impacts to mountain hydrology and ecology.

Oyler and his co-authors applied statistical techniques to account for biases introduced when equipment was switched at SNOTEL sites in the mid-1990s to mid-2000s.

His revised datasets reduced the biases to reveal that high-elevation minimum temperatures were warming only slightly more than minimum temperatures at lower elevations.

“Observations from other station networks clearly show that the western U.S. has experienced regional warming,” Oyler said, “but to assess current and future climate change impacts to snowpack and important mountain ecosystem processes, we need accurate observations from the high elevation areas only covered by the SNOTEL network. The SNOTEL bias has likely compromised our ability to understand the unique drivers and impacts of climate change in western U.S. mountains.”

http://wattsupwiththat.com/2015/01/12/another-bias-in-temperature-measurements-discovered/

 

According to the Abstract:

Here we critically evaluate this network’s temperature observations and show that extreme warming observed at higher elevations is the result of systematic artifacts and not climatic conditions. With artifacts removed, the network’s 1991–2012 minimum temperature trend decreases from +1.16°C decade⁻¹ to +0.106°C decade⁻¹ and is statistically indistinguishable from lower elevation trends. Moreover, longer-term widely used gridded climate products propagate the spurious temperature trend, thereby amplifying 1981–2012 western U.S. elevation-dependent warming by +217 to +562%. In the context of a warming climate, this artificial amplification of mountain climate trends has likely compromised our ability to accurately attribute climate change impacts across the mountainous western U.S.

 

In other words, most of the warming recorded by NOAA in the western US since 1981 is spurious. For instance, the West Region, (which encompasses California and Nevada), shows a trend since 1981 of 0.4F/decade. The real figure may be as low as 0.1F.

(In addition to this “West” region, there are also the Northwest and Southwest ones, both of which include a large number of SNOTEL stations).

 

http://www.ncdc.noaa.gov/cag/

 

Not only do the biased SNOTEL temperatures have a significant effect on the mountainous areas, where it follows there is little other monitoring, but, as the paper points out, the errors are propagated over a wider area.

This is because they are used for the purpose of infilling USHCN sites at lower elevations, where data is missing. For instance, in Nevada, of the thirteen USHCN stations, seven have estimated data. (See Appendix). 

 

I asked NOAA at the time what action they would be taking to correct for these errors, but have had no response.  

This really is a scandal. We are not just talking about an odd station out by a few tenths of a degree. The area affected by these spurious temperatures must account for nearly a third of the country, and the size of the error is said to be huge.

If this was any other field of science, a batch of erroneous , or even suspect, data such as this would be thrown out immediately.

Ironically, the paper’s Introduction states:

 

 

NOAA are keen to homogenise when it helps to cool the past, but don’t seem very interested when it might do the opposite.

Of course, it may be that NOAA are this minute investigating the problem and taking action.

But I am not holding my breath.  

 

 

 

APPENDIX

Nevada USHCN Stations – Number of Estimated Months in 2013 (Latest available)

 

Location	No of Months Estimated
Austin	12
Battle Mtn	0
Boulder City	12
Elko	0
Fallon	0
Golconda	12
Lovelock	0
McGill	11
Mina	5
Reno	3
Searchlight	0
Wells	12
Winnemucca	0