By Anthony Watts – Re-Blogged From WUWT
I’ve been saying for years that surface temperature measurements (and long term trends) have been affected by encroachment of urbanization on the placement of weather stations used to measure surface air temperature, and track long term climate. In doing so we found some hilariously bad examples of climate science in action, such as the official USHCN climate monitoring station at the University of Arizona, Tucson:
I have published on the topic in the scientific literature, and found this to be true based on the science we’ve done of examining the USHCN and applying the siting methodology of Leroy 2010.
In Fall et al, 2011 we discovered that there was a change to the diurnal temperature range (DTR). It decreased where stations had been encroached upon, because of the heat sink effect of man-made materials (asphalt, concrete, bricks, etc.) that were near stations.
For layman readers that don’t know what diurnal variation is, it is the daily variation of temperature due to the variation of incoming solar radiation from rotation of the earth on its axis.
It looks like this:
Here is what we found; in the best-sited stations, the diurnal temperature range in the lower 48 states has no century-scale trend, but the poorly sited stations had a reduction in DTR:
These results suggest that the DTR in the United States has not decreased due to global warming, and that analyses to the contrary were at least partly contaminated by station siting problems. Indeed, DTR tended to increase when temperatures were fairly stable and tended to decrease when temperatures rose.
Fall, S., A. Watts, J. Nielsen-Gammon, E. Jones, D. Niyogi, J. Christy, and R.A. Pielke Sr., 2011: Analysis of the impacts of station exposure on the U.S. Historical Climatology Network temperatures and temperature trends. J. Geophys. Res., in press. Copyright (2011) American Geophysical Union.
A few years back in 2012, I noted that NOAA was doing an experiment to prove or disprove what we learned.
Initial funding was provided this year by the USRCRN Program for a multi-year experiment to better understand the thermal impacts of buildings with parking lots on air temperature measurements. A site near the offices of ATDD will be instrumented to measure accurately the air temperature and other variables at multiple distances from the potential thermal heat source, corresponding to the distances from thermal sources used in classifying USCRN stations (Figure 7).
This study will have several applied and practical outcomes. Determining the downwind range of influence of a typical building will be important for understanding built environment impacts on surface air temperature measurements. Other measurements of radiation and heat fluxes will help illuminate the physical processes responsible for any detected heat transfers. Finally, this information will help influence future USCRN/USRCRN siting decisions. Additional insight is being sought by collaborating with National Weather Service (NWS) and National Institute for Standards and Technology (NIST) on extensions of the basic project. This effort promises to be greatly useful to understanding climate quality temperature measurements and how they can be influenced by the station site environment.
They have finally published. (h/t to Steve Mosher) Guess what? Like I’ve said all along (and been excoriated for saying so) they found exactly what we did.
Impacts of Small-Scale Urban Encroachment on Air Temperature Observations
Ronald D. Leeper, John Kochendorfer, Timothy Henderson, and Michael A. Palecki
Abstract (bold mine)
A field experiment was performed in Oak Ridge, TN, with four instrumented towers placed over grass at increasing distances (4, 30, 50, 124, and 300 m) from a built-up area. Stations were aligned in such a way to simulate the impact of small-scale encroachment on temperature observations. As expected, temperature observations were warmest for the site closest to the built environment with an average temperature difference of 0.31 and 0.24 °C for aspirated and unaspirated sensors respectively. Mean aspirated temperature differences were greater during the evening (0.47 °C) than day (0.16 °C). This was particularly true for evenings following greater daytime solar insolation (20+ MJDay−1) with surface winds from the direction of the built environment where mean differences exceeded 0.80 °C. The impact of the built environment on air temperature diminished with distance with a warm bias only detectable out to tower-B’ located 50 meters away.
The experimental findings were comparable to a known case of urban encroachment at a U. S. Climate Reference Network station in Kingston, RI. The experimental and operational results both lead to reductions in the diurnal temperature range of ~0.39 °C for fan aspirated sensors. Interestingly, the unaspirated sensor had a larger reduction in DTR of 0.48 °C. These results suggest that small-scale urban encroachment within 50 meters of a station can have important impacts on daily temperature extrema (maximum and minimum) with the magnitude of these differences dependent upon prevailing environmental conditions and sensing technology.
And, we’ve published at AGU on the effects of siting on 30 year temperature trends:
The quality of temperature station siting matters for temperature trends
30 year trends of temperature are shown to be lower, using well-sited high quality NOAA weather stations that do not require adjustments to the data.
NEW STUDY OF NOAA’S U.S. CLIMATE NETWORK SHOWS A LOWER 30-YEAR TEMPERATURE TREND WHEN HIGH QUALITY TEMPERATURE STATIONS UNPERTURBED BY URBANIZATION ARE CONSIDERED
Figure 4 – Comparisons of 30 year trend for compliant Class 1,2 USHCN stations to non-compliant, Class 3,4,5 USHCN stations to NOAA final adjusted V2.5 USHCN data in the Continental United States
EMBARGOED UNTIL 13:30 PST (16:30 EST) December 17th, 2015
SAN FRANCISCO, CA – A new study about the surface temperature record presented at the 2015 Fall Meeting of the American Geophysical Union suggests that the 30-year trend of temperatures for the Continental United States (CONUS) since 1979 are about two thirds as strong as officially NOAA temperature trends.
Using NOAA’s U.S. Historical Climatology Network, which comprises 1218 weather stations in the CONUS, the researchers were able to identify a 410 station subset of “unperturbed” stations that have not been moved, had equipment changes, or changes in time of observations, and thus require no “adjustments” to their temperature record to account for these problems. The study focuses on finding trend differences between well sited and poorly sited weather stations, based on a WMO approved metric Leroy (2010)1for classification and assessment of the quality of the measurements based on proximity to artificial heat sources and heat sinks which affect temperature measurement. An example is shown in Figure 2 below, showing the NOAA USHCN temperature sensor for Ardmore, OK.
Dare I call this new NOAA paper vindication?
Or, by doing so will the rabble of global warming zealots led by schmucks like Dr. Michael Mann find yet another reason to label me a “Koch funded science denier”?
I could use a beer right about now. You can support the work here.