crickham said-
I stumbled upon this paper that analyzes GISS algorithms for homogenizing temp data and removing urban bias. I thought you might like to read it.
it certainly clears up quite a few of the adjustments and the methods for doing so.
http://oprj.net/oprj-archive/climate-science/31/oprj-article-climate-science-31.pdf
I, for one, have always been suspicious of new figures for old readings.
this really is the oddest part. why does GISS basically stop adjusting after 1990?
this paper really is amazing. I recommend it for anyone who wants to know more about the nuts and bolts of how global temp datasets are made.
Oh well, I'm sure without even the skimpiest of investigations we can safely assume the adjustments were made solely for political reasons and that there was no valid justification for them whatsoever. That's good science. Right Ian?
I stumbled upon this paper that analyzes GISS algorithms for homogenizing temp data and removing urban bias. I thought you might like to read it.
it certainly clears up quite a few of the adjustments and the methods for doing so.
http://oprj.net/oprj-archive/climate-science/31/oprj-article-climate-science-31.pdf
Their approach of applying temperature adjust- 751
ments in reverse chronological order, i.e., adding the 752
calculated current urban bias to the start of the 753
record, rather than subtracting it from the end ofthe record, appears unwise for several reasons:
756 It is non-intuitive: why should we claim that, for
757 instance, the Tokyo record was artificially too
758 cold in 1900 because it now has a substantial
759 urban heat island, rather than recognising that
760 it is currently artificially too warm (Figure 3)?
761 By forcing their adjustments to be zero for the
762 most recent year, they have to identify the other
763 end of their adjustments (i.e., the exact onset of
764 the urbanization bias), with a much higher pre-
765 cision and accuracy than they would otherwise.
766 As urbanization bias is generally a progressive
767 phenomenon, it is easier to accurately identify
768 its presence near the end of a record after it has
769 grown substantial, than to accurately pinpoint
770 the year in which urbanization bias began af-
771 fecting the record.
772 As urbanization is an ongoing phenomenon, it
773 means that the entire set of adjustments must
774 be recalculated and changed each month, as the
775 latest data arrives. This can lead to considerable
776 confusion comparing results from one month to
777 the next, as each urban stations record contin-
778 ually has its history rewritten.
779 As NASA GISS have been rather terse in justify-
780 ing their basis for taking this approach[1517], it
781 is liable to lead to suspicion amongst those scep-
782 tical of the reliability of NASA GISS global tem-
783 perature estimates[51]. Indeed, Hansen et al.,
784 2010 recently complained of being the victims of
785 unfair suspicion from their critics[17]. Perhaps
786 this is part of the reason.
I, for one, have always been suspicious of new figures for old readings.
In other words, the highly urbanized subset shows 681
considerably more warming than the average for the 682
full dataset. This suggests that a substantial compo- 683
nent of this warming is urbanization bias. So, if the 684
NASA GISS urbanization adjustments are reliable, 685
they should have substantially reduced the trend for 686
the adjusted subset. From the bottom panel of Fig- 687
ure 12, we can see that, up to about 1980, the adjust- 688
ments have indeed substantially reduced the warm- 689
ing trend, e.g., the 1895-1980 linear trend is reduced 690
from +1.02◦C/century for the unadjusted subset to 691
+0.21◦C/century for the adjusted subset. However, 692
after about 1990, there is almost no reduction, and 693
the 1990-2011 linear trend for both subsets is al- 694
most the same (+2.16◦C/century for unadjusted and 695
+2.04◦C/century for adjusted). 696
This is more immediately obvious from Figure 13, 697
where the gridded mean adjustment for the subset is 698
plotted. Although the mean adjustments do not be- 699
gin until about 1895, there is an almost linear mean 700
.....
The reduction in NASA GISS adjustments since
707 the 1980s is in direct contrast to the actual urbaniza-
708 tion of the associated metropolises. As can be seen
709 from the bottom panel of Figure 13, the total pop-
710 ulation of the 47 urban metropolises associated with
711 the stations has more than trebled since 1950 (129
712 million in 1950 to 434 million in 2010). While pop-
713 ulation is not an exact measure of urbanization[46,
714 47], it is a reasonable indicator. So, the fact that the
715 adjustments for the subset begin decreasing, rather
716 than increasing, in the 1980s suggests a serious flaw
717 in the NASA GISS urbanization adjustments
We note that by removing a lot of urbanization
719 bias from the pre-1980s records, but not much from
720 the post-1980s records, this artificially makes global
721 temperatures for recent decades appear more unusual
722 than if they had been unadjusted. This is important,
723 because the public seems particularly interested in
724 establishing which years are globally the hottest on
725 record, e.g., see Refs.
this really is the oddest part. why does GISS basically stop adjusting after 1990?
this paper really is amazing. I recommend it for anyone who wants to know more about the nuts and bolts of how global temp datasets are made.