Adjustment Effects on Temperature Trends: Part 3 – Effects by Latitude

Part 3 looks at a geographical distribution of how adjustments affect temperature trends.  I have not dug down to the country level, although I wouldn’t rule it out for some future investigation. I did look at distribution by WMO region, but very little to see there. However, when I looked at distribution by lattitude band, a clear warming bias stood out for 24N to 44N (Figure 1). 

 
Figure 1. Distribution by latitude band showing how adjustments affect the warming or cooling trends of temperature data sets.
As with Part 1 and Part 2 I immediately wanted to see the detail of the magnitude of adjustment.  Figure 2 shows the bias very well – again for 24N to 44N. There is indeed a strong warming bias in the adjustments, with huge adjustments of 1-2.5 degC/Century.


Figure 2. A breakdown of the magnitude of temperature trend adjustment by latitude band.
There are only very slight biases in other latitidue bands, if they are detectable at all. I was tempted not to even show them, however here are the graphs for 64N to 90N (Figure 3) where there are cooling adjustments, and the bands either side of the Equator – 24N to 24S (Figure 4).  There is also a cooling bias in Equator to 24N.  Again these are subtle.

                            

Figure 3. Adjustments for 64N to 90N       Figure 4. Adjustments for bands spanning the Equator.

I suppose until I put all this together I am not sure of the significance this bias in adjustment. At present I cannot say it is intentional that so many small warming biases have crept in with each adjustment, but I am more sure than ever that the adjustments now must be justified.

So where next with this?  Well, at the moment I have a hankering to examine the effect of the major fall off of stations after 1990, but I guess I’ll have to play with the data for a while to see what it shows.

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4 Responses to Adjustment Effects on Temperature Trends: Part 3 – Effects by Latitude

  1. KevinS says:

    Verity,

    This is a very intersting analysis.

    However, looking at the other threads on digginintheclay (DITC) (e.g. Mapping global warming) it appears to me that the size of any bias introduced into the trends via the adjustements is small in comparison to the clear warming tends evident in the raw (i.e. unadjusted) data itself (e.g. look at the raw and adjusted maps for the 1970 to 2010 time period – there’s barely any difference between them.)

    Your Figure 1 seems to indicate that there is more or less an equal amount of cooling as warming introduced courtesy of the adjustments at all latitude bands except the 24N to 44N band. This happens to be the latitude band that contains the largest number of Northern Hemisphere stations as it includes the USA, Europe, most of China etc, so what is to say that the imbalance you show for this latitude band isn’t just an artefact of the no. of stations in this band compared to the other latitude bands?

    This latitude band also includes most of the stations that were added to the GHCN dataset that are ‘short lived’ i.e. sttaions where the data doesn’t start until about 1950 and ends in around 1992. This discrepancy in cooling versus warming trend could well be caused by the addition of this ‘short lived’ station data rather than as a result of the adjustments (but is most likely a component of both)?

  2. KevinS says:

    Verity,

    It might be an idea to produce a ‘stacked histogram’ showingthe no. of sttaions in each of the latitude bands given in Figure 1 and show teh counts for ‘long lived’ and ‘short lived’ stations as two separate series. That would then inform my discussions as to possible reasons for the disparity in cooling versus warming adjustments for teh 24N to 44N latitude band in my first post above.

  3. bruce says:

    It is amazing, with all of the adjustments and all, that the AGW advocates can accurately state that there has been global warming over the last century of 0.6 C. I am truly impressed at how they can do that.

    You mentioned that your next step is to look at the fallout of stations after 1990. Is there a list of the stations that are actually used? I have found US and Global lists, but these inclued all stations and do not show which ones are used.

    You have a great site and do great work. I hope you realize I was being sarcastic in my first paragraph. I think I’m going to start reading the “peer-reviewed” literature that gives credibility to the calculated global averages.

  4. VJones says:

    Bruce,
    thanks for the compliment. I did get your sarcasm and you echo our incredulity. We have the adjusted data whis gives the stations actually used and the years when they are used.

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