In message , nonononononononoonoo b o
writes
http://wattsupwiththat.com/2009/12/0...t-darwin-zero/

The explanation is he

http://www.economist.com/blogs/democ...entists?page=3
http://www.john-daly.com/darwin.htm

(Note that the second site is actually an AGW skeptic site)

In addition to adjustments needed because the thermometer type changes
there are two additional reason for the temperature adjustments specific
to Darwin. Firstly the weather station was moved in 1941 from a warmer
to a cooler location and secondly it was incorrectly screened at the old
site so the sun was shining directly on the thermometer.

"As previously advised, the main temperature station moved to the radar
station at the newly built Darwin airport in January 1941. The
temperature station had previously been at the Darwin Post Office in the
middle of the CBD, on the cliff above the port. Thus, there is a likely
factor of removal of a slight urban heat island effect from 1941
onwards. However, the main factor appears to be a change in screening.
The new station located at Darwin airport from January 1941 used a
standard Stevenson screen. However, the previous station at Darwin PO
did not have a Stevenson screen. Instead, the instrument was mounted on
a horizontal enclosure without a back or sides. The postmaster had to
move it during the day so that the direct tropical sun didn't strike it!
Obviously, if he forgot or was too busy, the temperature readings were a
hell of a lot hotter than it really was!"

The adjustments were made to bring it more into line with nearby weather
stations which had more accurate data.




And the result is that a cooling trend miraculously becomes a warming trend!

The reason it appeared to have a cooling trend is that the earlier
(pre-1941) data was recorded in a warmer location and the thermometer
was not shaded from the sun properly (as explained above). When those
early mistakes are corrected for then the cooling trend vanishes.

Let's try an example to make it clearer, say you buy an a new accurate
thermometer and find that the one you have previously been using always
read 2c above the real temperature and that the last 5 years data is
wrong.

Do you:

A) Correct for the mistake by taking 2c off the old readings

B) Throw all the data away and start again

You obviously try to correct the data. Now think about what happens if
someone looks at the uncorrected data, it will show a drop in
temperature when you bought your new thermometer and your data will show
a cooling trend. Look at the corrected data and that cooling trend
vanishes.

Clearer yet?

This kind of correction goes on all the time and what the AGW deniers
have done is dishonestly cherry picked an extreme example which shows
what they want. You are deliberately ignoring all the other weather
stations which did not have this problem.
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