Correcting the surface temperature record for UHI

Bob Tisdale
I agree with your argument, didn’t want to detour too far down that path. I agree there is the cumulative warming effects of more El Ninos during +PDO and cooling from La Ninas during -PDO. The warming in +PDO and El Ninos is net- there are cool pockets – e.g the southeast US just as there are regional warm pockets in La Nina (again southeast US).
The warm tripole of the +AMO corrrelates with general warmth across most NH continents on an annual basis, though can be offset by -PDO. When they are both negative – we are at our coldest, both positive, warmest.
Regards
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Adam, Slioch, et al
This quote from the secind link above
“What constitutes an urban site versus a rural site? Peterson and others who support the IPCC viewpoint consider a town with a population of less than 10,000 people to be rural and not to require any adjustment for urbanization. Nothing could be further from the truth.
Oke (1973) and Torok et al (2001) show that even towns with populations of 1000 people have urban heating of about 2.2 C compared to the nearby rural countryside. Since the UHI increases as the logarithm of the population or as about 0.73 log (pop), a village with a population of 10 has an urban warming of 0.73 C, a village with 100 has a warming of 1.46 C, a town with a population of 1000 people already has an urban warming of 2.2 C, and a large city with a million people has a warming of 4.4 C (Oke, 1973).
Try this thought experiment: In 1900, world population is 1 billion and in 2000, it is 6 billion for an increase of a factor of six. If the surface measuring stations are randomly distributed and respond to this population increase, it would equal 2.2 log (6) or 1.7 C, a number already greater than the observed warming of 0.6 C. If however we note that UHIs occur only on land or 29% of the Earth’s surface, than the net global warming would be 0.29*1.7 or 0.49 C which is close the observed warming. It is not out of the realm of possibility that most of the twentieth century warming was urban heat islands.”
As for the

Yes Adam, I would like to see what you come up with.
Slioch
See the difference NOAA GHCN vs UAH and RSS
http://icecap.us/images/uploads/NCDC-SAT.jpg

Adam (19:18:15) : “You are severely abusing the results of the Jones et al study whose main findings can be summarized as:
– London and Vienna had no UHI signal in temperature trends because the influence of the cities weren’t changing over time.
– Only very small UHI effects were implied for “land-based” datasets in China.
– Urban related warming was 0.1 degree C per decade from 1951–2004. ”
This is grossly misleading 1. No idea why Vienna and London are thrown in (hey, small, unrepresentative sample much?) 2. The warming over China in the entire period before urban warming is taken out is equivalent to .26 degrees C per decade-in line with the supposed global land trend:
http://hadobs.metoffice.com/crutem3/diagnostics/global/nh+sh
3. The after the fact land trend is .16 degrees per decade, which is much less, and is less than the global rate.
4. That’s especially problematic because that part of the world should be warming faster:
Ramanathan, V., M.V. Ramana, G. Roberts, D. Kim, C. Corrigan, C. Chung, and D. Winker, 2007. Warming trends in Asia amplified by brown cloud solar absorption. Nature, 448, 575-578.
The Jones et al. paper is quite frankly devastating.

@ur momisugly timetochooseagain (10:12:23) :
I do not question the results of the paper that Pielke refers to but I do question his statement:
Thus minimum temperatures over land are very sensitive to their immediate local environments. Their use to characterize minimum temperatures as being spatially representative over a larger area, such as used to diagnose global warming and cooling, are not appropriate.
I undertand how actual recorded local temperatures may be influenced, but why would the TREND in temperature at these places be affected?
It is not as if these locations are moving? Overnight temps are rising faster than afternoon temps which is not a surprise because of the convective nature of the afternoon boundary layer. Overnight layers may not be as stable as we have believed but they are certainly more stable than daytime layers. Pielke himself states this in the second link you provided:
In addition to the thermodynamic stability and wind speed, the nocturnal boundary layer is sensitive to changes in land surface characteristics, such as heat capacity [Carlson, 1986; McNider et al., 1995a]. Additionally, it is also much more sensitive to external forcing such as downward longwave radiation from greenhouse gas forcing, water vapor, clouds, or aerosols than is the daytime boundary layer [Eastman et al., 2001; Pielke and Matsui, 2005]. The main reason for this sensitivity is that the nocturnal boundary layer is shallower than the daytime boundary layer. Thus heating of the surface due to infrared radiation or changes in heat capacity or conductivity of heat from the soil is distributed through a smaller air layer.
Then Pielke summarizes with:
In summary, given the lack of observational robustness of minimum temperatures, the fact that the shallow nocturnal boundary layer does not reflect the heat content of the deeper atmosphere, and problems global models have in replicating nocturnal boundary layers, it is suggested that measures of large-scale climate change should only use maximum temperature trends.
Of course, then it means less AGW in that specific respect because max temps have warmed at a much lower rate. Strange that Pielke states how overnight temps are more strongly influenced by downwelling greenhouse gas IR so why would he remove a component that he is trying to measure?!
I still cannot see how TREND would be affected if one considers all of Pielke’s “problems”. For example, wouldn’t wind speed changes average out over the long haul so that the underlying trend sticks out?
Regarding the Peterson paper from 1998 as being ancient. Are we not looking at historical data and not just newer data? So what if we are looking at 1950 to 1990? Comparison between temperature trends of the full corrected land data set used in global temperature trend analysis and a subset of rural stations suggests there is very little residual effect of urbanization remaining in the data. And more importantly, this study was done well before surfacestations.org and parallels the NOAA analysis that some here think is a conspiracy.
Here are some newer articles that also refute Pielke’s claims:
http://hadobs.metoffice.com/urban/Parker_JClimate2006.pdf
Conclusion: The analysis of Tmin demonstrates that neither urbanization nor other local instrumental or thermal effects have systematically exaggerated the observed global warming trends in Tmin.
http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2FJCLI3431.1
Conclusion: comparison between U.S. Historical Climatology Network (HCN) time series from the full dataset and a subset excluding the high population sites indicated that the UHI contamination from the high population stations accounted for very little of the recent warming.
And of course IPCC WGI 2007 at http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter3.pdf
Conclusion: Urban heat island effects are real but local, and have not biased the large-scale trends. A number of recent studies indicate that effects of urbanisation and land use change on the land-based temperature record are negligible (0.006ºC per decade) as far as hemispheric- and continental-scale averages are concerned because the very real but local effects are avoided or accounted for in the data sets used.
So far the data suggests that “the rising tide lifted all boats” which seems common sense to me.

By the way, another way of looking at my last point without getting into the transient climate sensitivity is simply this: If you look at what the rise in CO2 in those ICECAP plots corresponds to on the temperature axis, you find that it is about 0.63 to 0.7 C per decade. By contrast, the IPCC AR1 WG1 Summary for Policymakers (SPM), available here http://www.ipcc.ch/ipccreports/ar4-wg1.htm states (on p. 12), “For the next two decades, a warming of about 0.2°C per decade is projected for a range of SRES emission scenarios.”