Foreword: I give thanks to Steve McIntyre for this analysis. Steve came to a conclusion similar to what I alluded to in my initial rebuttal where I said:
“For all I know, they could be comparing homogenized data from CRN1 and 2 (best stations) to homogenized data from CRN 345 (the worst stations), which of course would show nearly no difference.“
Steve does a superb job of deconstructing the memo’s undocumented results. Perhaps someday Dr. Thomas Peterson of NCDC will tell us how he did his analysis and show supporting data and methods. – Anthony
The NOAA Talking Points memo falls well short of a “full, true and plain disclosure” standard – aside from the failure to appropriately credit Watts (2009).
They presented the following graphic that purported to show that NOAA’s negligent administration of the USHCN station network did not “matter”, describing the stations as follows:
Two national time series were made using the same gridding and area averaging technique. One analysis was for the full data set. The other used only the 70 stations that surfacestations.org classified as good or best… the two time series, shown below as both annual data and smooth data, are remarkably similar. Clearly there is no indication for this analysis that poor current siting is imparting a bias in the U.S. temperature trends.
Figure 1. From Talking Points Memo.
Beyond the above sentence, there was no further information on the provenance of the two data sets. NOAA did not archive either data set nor provide source code for reconciliation.
The red graphic for the “full data set” had, using the preferred terminology of climate science, a “remarkable similarity” to the NOAA 48 data set that I’d previously compared to the corresponding GISS data set here (which showed a strong trend of NOAA relative to GISS). Here’s a replot of that data – there are some key telltales evidencing that this has a common provenance to the red series in the Talking Points graphic.
Figure 2. Plot of US data from www1.ncdc.noaa.gov/pub/data/cirs/drd964x.tmpst.txt
An obvious question is whether the Talking Points starting point of 1950 is relevant. Here’s the corresponding graphic with the 1895 starting point used in USHCN v2. Has the truncation of the graphic start at 1950 “enhanced” the visual impression of an increasing trend? I think so.
Figure 3. As Figure 2, but to USHCN v2 start
The Talking Points’ main point is its purported demonstration that UHI-type impacts don’t “matter”. To show one flaw in their arm-waving, here is a comparison of the NOAA U.S. temperature data set and the NASA GISS US temperature data set over the same period – a comparison that I’ve made on several occasions, including most recently here. NASA GISS adjusts US temperatures for UHI using nightlights information, coercing the low-frequency data to the higher-quality stations. The trend difference between NOAA and NASA GISS is approximately 0.7 deg F/century in the 1950-2008 period in question: obviously not a small proportion of the total reported increase.
Figure 4. Difference between NOAA and NASA in the 1950-2008 period. In def F following NOAA (rather than deg C)
As has been discussed at considerable length, the NASA GISS adjusted version runs fairly close to “good” CRN1-2 stations – a point which Team superfans have used in a bait-and-switch to supposedly vindicate entirely different NASA GISS adjustments in the ROW, (adjustments which appear to me to be no more than random permutations of the data, a point discussed at considerable length on other occasions.)
For present purposes, we need only focus on the observation that there is a substantial trend difference between NOAA and GISS trends.
Given that, when NOAA’s Talking Points claim that there is a supposedly negligible difference between the average of their “good” stations and the NOAA average (which we know to run hot relative to GISS), then arguably this raises issues about the new USHCN procedures.
Y’see, while NOAA doesn’t actually bother saying how it did the calculations, here’s my guess as to what they did. The new USHCN data sets (as I’ll discuss in a future post) ONLY show adjusted data. No more inconvenient data trails with unadjusted and TOBS versions.
When I looked at SHAP and FILNET adjustments a couple of years ago, one of my principal objections to these methods was that they adjusted “good” stations. After FILNET adjustment, stations looked a lot more similar than they did before. I’ll bet that the new USHCN adjustments have a similar effect and that the Talking Points memo compares adjusted versions of “good” stations to the overall average.
So what they are probably saying is this: after the new USHCN “adjustments” (about which little is known as the ink is barely dry on the journal article describing the new method and code for which is unavailable), there isn’t much difference between the average of good stations and the average of all stations.
If the NASA GISS adjustment procedure in the US is justified (and most Team advocates have supported the NASA GISS adjustment in the US), then the Talking Points memo merely demonstrates that there is something wrong with the new USHCN adjustments.