Will The Real Historical Temperature Record Please Stand Up
April 6th, 2008
John Goetz
http://www.climateaudit.org/?p=2964#more-2964
In February I wrote a post asking How much Estimation is too much
Estimation? I pointed out that a large number of station records
contained estimates for the annual average. Furthermore, the number of
stations used to calculate the annual average had been dropping
precipitously for the past 20 years. One was left to wonder just how
accurate the re****ted global average really was and how meaningful
rankings of the warmest years had become.
One question that popped into my mind back then was whether or not -
with all of the estimation going on - the historical record was static.
One could reasonably expect that the record is static. After all, once
an estimate for a given year is calculated there is no reason to change
it, correct? That would be true if your estimate did not rely on new
data added to the record, in particular temperatures collected at a
future date. But in the case of GISStemp, this is exactly what is done.
Last September I noted that an estimate of a seasonal or quarterly
temperature when one month is missing from the record depends heavily on
averages for all three months in that quarter. This can be expressed by
the following equation, where are the months in the quarter (in no
particular order) and one of the three months is missing:
In the above, T is temperature, q is the given quarter, n is the given
year, and N is all years of the record.
One can readily see that as new temperatures are added to the record,
the average monthly temperatures will change. Because those average
monthly temperatures change, the estimated quarterly temperatures will
change, as will the estimated annual averages.
Interestingly, application of the "bias method" used to combine a
station's scribal records can have a ripple effect all the way back to
the beginning of a station's history. This is because the first annual
average in every scribal record is estimated, and the bias method relies
on the overlap between all years of record, estimated or not. Recall
that annual averages are calculated from December of the prior year
through November of the current year. However, all scribal records begin
in January (well, I have not found one that does not begin in January),
so that first winter average is estimated due to the missing December
value. Thus, with the bias method, at least one of the two records
contains estimated annual values.
Of course, it is fair to ask whether or not this ultimately has any
effect on the global annual averages re****ted by GISS. One does not have
to look very hard to find out that the answer is "yes".
On March 29 I downloaded the GLB.Ts.txt file from GISS and compared it
to a copy I had from late August 2007. I was surprised to find several
hundred differences in monthly temperature. Intrigued, I decided to take
a trip back in time via the "Way Back Machine".
Here I found 32 versions of GLB.Ts.txt going back to September 24, 2005.
I was a bit disappointed the record did not go back further, but was
later surprised at how many historical changes can occur in a brief 2
1/2 years.The first thing I did was eliminate versions where no changes
to the data were made. I then compared the number of monthly differences
between the remaining sequential records and built the following table.
Here I show the "Prior" record compared to the next sequential record
(referred to as "Current"). The number of changes made to the monthly
record between Prior and Current is shown in the "Updates" column (this
column does not count additions to the record - only changes to existing
data are counted). The number of valid months contained in the Prior
record is in the "Months" column. "Change" is simply the percent Updates
made to Months.
On average 20% of the historical record was modified 16 times in the
last 2 1/2 years. The largest single jump was 0.27 C. This occurred
between the Oct 13, 2006 and Jan 15, 2007 records when Aug 2006 changed
from an anomoly of +0.43C to +0.70C, a change of nearly 68%.
Wow.
The next question I had was "how often are the months within specific
years modified?" As can be seen in the next chart, a surprising number
of the earliest monthly averages are modified time and again.
I was surprised at how much of the pre-Y2K temperature record changed!
My personal favorite change was between the August 16, 2007 file and the
March 29, 2008 file. Suddenly, in the later file, the J-D annual
temperature for 1880 could now be calculated. In all previous versions
the temperature could not be determined.
But some will want to know only how this process affects the rankings
for the top 10 warmest years. Because the history goes back to the
middle of 2005, I explored this question only for the years before 2005.
While the overall ranking from top to bottom does change from one record
to the other, the top 10 prior to 2005 does not change much. However,
the top two do exchange position frequently, as can be seen from the
following table:
I will note that the overall trend in changes between now and Sep. 24,
2005 is very close to zero. If one compares the latest file with the one
from Sep 24, 2005, it can be seen that the earliest and latest years are
adjusted lower today than in 2005, while the middle years are adjusted
higher. However, this is purely coincidence. If one compares the file
from Aug. 2007 with the latest file, it appears the earliest
temperatures have been adjusted downward, leading to an overall upward
trend. Surely other comparisons will yield a downward tend. It is by
pure chance that we have selected two endpoint datasets that appear to
have no effect on the tend.
It is at this point I would like to ask, does anyone have a copy of the
GISS monthly and annual temperatures - the equivalent to GLB.Ts.txt -
from a date earlier than Sep. 24, 2005?
In the meantime, will the real historical record please stand up?
--
Warmest Regards
Bonzo
The Fourth Re****t of the IPCC might just as well decree the
suppression of all climatology textbooks, and replace them in our
schools with press communiqués. ... Day after day, the same mantra -
that 'the Earth is warming up' - is churned out in all its forms. As
'the
ice melts' and 'sea level rises' the Apocalypse looms ever nearer!
Without realizing it, or perhaps without wi****ng to, the average
citizen in bamboozled, lobotomized, and lulled into mindless acceptance.
.... Non-believers in the greenhouse scenario are in the
position of those long ago who doubted the existence of God ...
Marcel Leroux
It should be abundantly clear by now that the AGW hypothesis is
contradicted by the facts/measurements/observations and should
therefore be abandoned and be substituted by a hypothesis which
better matches the facts.
- Hans Labohm
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