Why would NASA be cc-ing Gavin Schmidt?
RPM1
By Steve McIntyre
I observed recently that Hansen's GISS series contains an apparent error in
which Hansen switched the source of GISS raw from USHCN adjusted to USHCN
raw for all values January 2000 and later. For Detroit Lakes MN, this
introduced an error of 0.8 deg C. I've collated GISS raw minus USHCN
adjusted for all USHCN sites (using the data scraped from the GISS site, for
which I was most criticized in Rabett-world). Figure 1 below shows a
histogram of the January 2000 step for the 1221 stations (calculated here as
the difference between the average of the difference after Jan 2000 and for
the 1990-1999 period.) The largest step occurred in Douglas AZ where the
Hansen error is 1.75 deg C! There is obviously a bimodal distribution.
Next here is a graph showing the difference between GISS raw and USHCN
adjusted by month (with a smooth) for unlit stations (Which are said to
define the trends). The step in January 2000 is clearly visible and results
in an erroneous upward step of about 0.18-0.19 deg C. in the average of all
unlit stations. I presume that a corresponding error would be carried
forward into the final GISS estimate of US lower 48 temperature and that
this widely used estimate would be incorrect by a corresponding amount. The
2000s are warm in this record with or without this erroneous step, but this
is a non-negligible error relative to (say) the amounts contested in the
satellite record disputes.
UPDATE:
On the weekend, I notified Hansen and Ruedy of their Y2K error as follows:
Dear Sirs,
In your calculation of the GISS "raw" version of USHCN series, it appears
to me that, for series after January 2000, you use the USHCN raw version
whereas in the immediately prior period you used USHCN time-of-observation
or adjusted version. In some cases, this introduces a seemingly unjustified
step in January 2000.
I am unaware of any mention of this change in procedure in any published
methodological descriptions and am puzzled as to its
rationale. Can you clarify this for me?
In addition, could you provide me with any documentation (additional to
already published material) providing information on the
calculation of GISS raw and adjusted series from USHCN versions, including
relevant source code.
Thank you for your attention,
Stephen McIntyre
Today I received the following response:
Dear Sir,
As to the question about documentation, the basic "GISS Surface
Temperature Analysis" page starts with a "Background" section whose first
paragraph contains the sentence: "Input data for the analysis ,., is the
unadjusted data of GHCN, except that the USHCN station records were replaced
by a later corrected version". A similar statement appears in the "Abstract"
and the "Introduction" section of our 2001 paper (JGR Vol 106, pg
23,947-23,948). The Introduction explains the above statement in more
detail.
In 2000, USHCN provided us with a file with corrections not contained in
the GHCN data. Unlike the GHCN data, that product is not kept current on a
regular basis. Hence we used (as you noticed) the GHCN data to extend those
data in our further updates (2000-present).
I agree with you that this simple procedure creates an artificial step if
some new corrections were applied to the newest data, rather than bringing
the older data in sync with the latest measurements - as I naively assumed.
Comparing the 1999 data in both data sets showed that in about half the
cases where the 1999 data were changed, the GHCN data were higher than the
USHCN data and in the other half it was the other way round with the
plus-corrections slightly outweighing the minus-corrections.
Although trying to eliminate those steps should have little impact on the
US temperature trend (much less the global trend), it seems a good idea to
do so and I'd like to thank you for bringing this oversight to our
attention.
When we did our monthly update this morning, an offset based on the last
10 years of overlap in the two data sets was applied and our on-line
documentation was changed correspondingly with an acknowledgment of your
contribution. This change and its effect will be noted in our next paper on
temperature analysis and in our end-of-year temperature summary.
The effect on global means and all our tables was less than 0.01 C. In the
display most sensitive to that change - the US-graph of annual means - the
anomalies decreased by about 0.15 C in the years 2000-2006.
Respectfully,
Reto A Ruedy
Well, my estimate of the impact on the US temperature series was about
0.18-0.19 deg C., a little bit more than Ruedy's 0.15 deg C. My estimate
added a small negative offset going into 2000 to the positive offset of
about 0.15-0.16 after 2000 - I suspect that Ruedy is not counting both
parts, thereby slightly minimizing the impact. However, I think that you'll
agree that my estimate of the impact of the impact was pretty good, given
that I don't have access to their particular black box.
Needless to say, they were totally unresponsive to my request for source
code. They shouldn't be surprised if they get an FOI request. I'll post some
more after I chance to cross-check their reply.
As to the impact on NH and global data, I've noted long before this exchange
that the non-US data in GHCN looks more problematic to me than the US data
and it would be really nice if surfacestations.org starting getting some
international feedback. Ruedy's reply was copied to Hansen and to Gavin
Schmidt. I'm not sure what business it is of Gavin's other than his "private
capacity" involvement in a prominent blog.
Roger Coppock
> The effect on global means and all our tables was less than 0.01 C.
> Respectfully,
> Reto A Ruedy
For global warming, that is not a big deal.
It does change the US means, but US means
aren't GLOBAL warming, because the US is
not the globe.
Bonzo
"Roger Coppock" <rcop...@adnc.com> wrote in message
news:1186749701.1...@q4g2000prc.googlegroups.com...
Meaningless means!
Regards
Bonzo
[average land temperature is ] "impossible to measure. is a fiction. nobody
knows what it is. there's no way you can measure it." Freeman Dyson Professor of
Physics, Institute for Advanced Study,Princeton, Fellow of the American Physical
Society, Member of the U.S. National Academy of Sciences, Fellow of the Royal
Society of London
ExterminateAllRepubliKKKans
"Bonzo" <boo...@optusnt.com.au> wrote
> Meaningless means!
Bozo here is the poster clown for meaningless.