The systematic time of observation bias would be of little concern with regard to temperature trends provided that the observation time at a given station did not change during its operational history. As shown in Fig. 3, however, there has been a widespread conversion from afternoon to morning observation times in the HCN. Prior to the 1940s, for example, most observers recorded near sunset in accordance with U.S. Weather Bureau instructions. Consequently, the U.S. climate record as a whole contains a slight positive (warm) bias during the first half of the century. A switch to morning observation times has steadily occurred during the latter half of the century to support operational hydrological
requirements. The result is a broad-scale reduction in mean temperatures that is simply caused by the conversion in the daily reading schedule of the Cooperative Observers. In other words, the gradual conversion to morning observation times in the United States during the past 50 years has artificially reduced the true temperature trend in the U.S. climate record (Karl et al. 1986; Vose et al. 2003; Hubbard and Lin 2006; Pielke et al. 2007a).

Has anyone attempted to extrapolate the adjustments into the future? Just by eyeballing the charts it looks like the adjustments could becomes several degrees by 2100.

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Richard, Richard…. Haven’t been keeping up with the news?

MIT did just that study a few weeks ago, and came up with a whirling prediction circular pieplate (er, template) that ALL corrected UHI thermometers will read +9 degrees by the year 2010.

Come on. Ya gotta keep up better!

For your money, this might be a better investment.

Pielke, Roger A., Christopher A. Davey, Dev Niyogi, Souleymane Fall, Jesse Steinweg-Woods, Ken Hubbard, Xiaomao Lin, Ming Cai, Young-Kwon Lim, and Hong Li (2007), Unresolved issues with the assessment of multidecadal global land surface temperature trends, J Geophys Res, 112, D24S08.[CrossRef]

Mitchell, J.M., Effect of changing observation time on mean temperature, Bull. Am. Meteorol. Soc., 39, 83-89, 1958.

I can’t retrieve it from BAMS. The search function will not bring it up. It appears to be the first cited paper.

“Little black balloons of CO2 floating up into the sky….”

Let’s see, the atomic mass of N2 is what? And O2 is what? So balloons filled with CO2, with it’s greater mass, is “floating up into the sky”. They must be using one of the IPCC’s models to get that result.”

Well, as N2 makes up 78% of the atmosphere, I used that in an e-mail to the person at the “contact us” link at that site. So I e-mail the contact stating that N2 has an atomic weight of about 15, whereas CO2 is 44. Pointed out the fact that CO2 cannot “float up into the sky as if it is lighter than air and in a black balloon”, political spin and misinformation. Pointed out the fact that mercury (In the ecobulbs) is infinitely more poisonous than CO2 (Reference to Japan and people eating fish contaminated with mercury).

No response.

Here is a paper by Karl et al on the MMTS adjustment.

Thanks for the link to the Karl 1986 paper. But this paper describes a method for estimating TOBS and does not contain a study of actual TOBS trends. However, it does contain a table that shows a continuous trend from AM to PM measurements from 1931 to 1984 (percentage of AM readings goes from 14 to 42). Unfortunately they do not give the source of this data, which is surprising in a scientific paper. Do you have a link to actual scientific studies of the TOBS trends? Many thanks.
Chris

I appreciate the additional information and clarification.