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GISS Cooling The Past

May 26, 2014

By Paul Homewood


I and others have reported frequently on how NCDC have cooled historic temperatures for the US, with the result that the warming trend is accentuated.

The same thing has been happening on a global level with GISS. I have managed to obtain from the UK Met Office a copy of the GISS dataset, as it had been originally published in April 2005 (see Appendix).

The chart below compares that dataset with the latest version, available here.

As can be seen, temperature anomalies have been reduced, on the latest version, for nearly every year up to 1969. Subsequently, every year’s anomaly has been adjusted upwards.

Typically, temperatures during the 1930’s/40’s have been adjusted down by about 0.06C, while recent ones have been increased by a similar amount. This gives a net increase of over 0.10C.

Bearing in mind that the temperature rise, currently claimed by GISS, between 1940 and last year is 0.49C, at least a fifth of this is accounted for by adjustments to historical data.





It’s funny how the adjustments always seem to run the same way! Unfortunately, there were no satellites around in the 1940’s to offer a crosscheck.


BTW – I have been asked before about uncertainty estimates. GISS show these on their graph below, with the green bars. The current margin looks to be about 0.10C, and back in the 1940’s, closer to 0.20C.

Given these uncertainties, adjustments and likely underestimation of UHI, how much of the claimed increase since 1940 is real?







The 2005 version of the GISS dataset.






  1. May 26, 2014 9:16 pm

    Reblogged this on the WeatherAction Blog.

  2. Paul Burtwistle permalink
    May 26, 2014 9:57 pm

    Hi Paul,

    Just in case you haven’t seen it, there is a review of the temperature amendments process that GISS uses to adjust RAW data sets for UHI etc. Its available here –

    The report is in the peer review process just now and is pretty scathing on GISS procedures around this topic. Its well worth a read.

    Regards and keep up the good work,

    Paul Burtwistle.

  3. May 27, 2014 9:27 am

    Is there an audit trail for the changes? Steve Goddard, of course, at Real Science, has been tracking these guys abuse of the temperature records for some time

  4. Andy DC permalink
    May 28, 2014 12:50 am

    Most ordinary people are surprised when they learn that the global warming claims are largely based on altered data. The question is how do we educate the public with respect to this matter?

  5. May 28, 2014 2:17 pm

    Thanks, Paul. I have saved a few GISS Global Land-Ocean Temperature Index graphs over time. It is amazing to see how they change the past with every iteration.

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