This website has been presenting a segment called `Station of the Week' in which an individual meteorological station record is presented to demonstrate temperature trends over a long period to see to what extent, if any, the claimed `global warming' is manifested at stations where local effects like urbanisation are known to be minimal.

At the end of March 2000, the record at Darwin was presented, based on data obtained from the Goddard Institute (GISS) which compiles thousands of station records from around the world to produce those global graphs which show a warming of up to +0.7°C in the last 100 years.

But there is something peculiar about Darwin, a tropical site. It shows an overall cooling. But that cooling was mostly done in a period of only 3 years between 1939 and 1942. Here is the record -

Ken Parish, a resident of Darwin and who is a previous guest author on this site with his paper "The Big Bangs", investigated this record and presents his findings in the following set of emails sent to me.

Subject: Darwin's population
Date: Tue, 28 Mar 2000 20:44:34 +0930
From: "legalnet" <kparish@legalnet.net.au>
To: "John Daly" <daly@vision.net.au>

Dear John,

I haven't browsed your website for a few days until now. I see that Darwin (where I live) is your station of the week. However, you say that Darwin is a city of around 50,000 people. In fact the total Darwin urban area (which includes Palmerston and Litchfield Shire) has recently passed 100,000 (from memory it is now around 106,000). I don't know where you get the figures, but an error of 100% is pretty spectacular! It may be that you looked just at the population for Darwin without Palmerston or Litchfield Shire (which are all part of the Darwin greater urban area - in the same sense that Parramatta and Campbelltown are part of Sydney).

The ABS web page shows the population of Darwin as 86,600 as at the 1998 census, with an annual growth rate of over 10%. That growth rate has continued over the last 2 years. Moreover, the ABS figure includes Palmerston but not Litchfield Shire. This is a perfect illustration of how attempting to adjust temperature data for urban heat island effects without knowing the basis for population figures must inevitably result in gross errors.

However, it should be noted that Darwin's urban growth has been fairly sprawling, with a satellite town development model used (very much like Canberra in the tropics - in fact Darwin's northern suburbs and Palmerston were designed by the same town planners). The result is that there is no dense conurbation, rather a pleasant sprawl of green suburbs and rural residential 1-5 acre blocks. Moreover, the main temperature station (as in most places) is at Darwin airport. However, unlike a lot of airports, it is not closely surrounded by urban development, because the Australian Air Force continues to own large tracts of surrounding land. The result is that, despite the population having more than doubled since Cyclone Tracy in 1974, I would not expect to see any significant urban heat island effect, and that is precisely what the temperature record shows.

Regards Ken Parish

From: John L. Daly <daly@vision.net.au>
To: legalnet <kparish@legalnet.net.au>
Date: Wednesday, March 29, 2000 5:17 AM
Subject: Re: Darwin's population

Dear Ken

Thanks for the info on Darwin. Obviously, being your home turf you would have that vital local knowledge. It does show that some local knowledge is needed for all the thousands of stations worldwide that make up the global mean as each one has its own special characteristics. That problem alone makes it very problematic to simply crunch the numbers of each one without first determining how those numbers are created.

I was puzzled in the record by the cooling step-down during the early 1940s. It does not seem natural to me and coincides with the early part of the war, suggesting a site change or an instrument change.

Regards John Daly

Subject: Darwin temperature record
Date: Wed, 29 Mar 2000 08:18:53 +0930
From: "legalnet" <kparish@legalnet.net.au>
To: "John Daly" <daly@vision.net.au>

Further to my reply of a few minutes ago, the dust and smoke from bombing would have been further increased by the influx of military personnel which immediately followed the first bombing raid in February 1942. Army and airforces were rushed to Darwin, and by early 1943 there were some 300,000 military personnel in and around Darwin. Literally dozens of new airfields and scores of military encampments were carved out of the tropical scrubland, which was cleared and burned.

One may hypothesise that this resulted in a significantly increased and continuous loading of dust and soot in the local atmosphere. However, I note from your graph that the unnatural-looking fall seems to have occurred between 1939 and 1942. This suggests that shifting of the station location may be the more probable explanation for the discontinuity. I will try to check the precise timing of the move. I certainly know that the new airfield was opened at around that time. Both the new airfield and the old civil airfield at Fannie Bay were still in operation at the time of the first bombing raid in February 1942, but the civil airfield was closed shortly afterwards.

Regards Ken Parish

Subject: Darwin temperature record
Date: Wed, 29 Mar 2000 09:34:09 +0930
From: "legalnet" <kparish@legalnet.net.au>
To: "John Daly" <daly@vision.net.au>

Dear John,

I have spoken to someone from the Climate section of the Darwin Bureau of Meteorology. They advise that the Darwin temperature station was moved to its present location at the radar station at Darwin airport in early 1941 (when the radar station was built). At this time the airport was very much "out in the scrub" with no surrounding development at all. Indeed old photos in books I have on the bombing of Darwin suggest (though not conclusively) that the runway was not even concrete or bitumen-surfaced at that time. Thus no urban heat island effect.

Prior to the 1941 move, there were 3 main temperature measurement locations, at Government House, the old Post Office, and the Botanical Gardens. The meteorologist I spoke to was not sure which of these was designated as the site for the official Darwin record at that time. He was going to research the question and get back to me. However, both Government House and the old Post Office were/are in the very centre of town, and located on a cliff immediately above the port (where the railway terminated and minerals etc were loaded on ships). Although the Darwin CBD was much less built-up then than it is now, I would expect that a station at either of those 2 locations would have been subject to a reasonably significant urban heat island effect. On the other hand, if the official station was at the Botanical Gardens, there would not have been such an effect. However, the skyline effect of dense foliage at the lush Botanical gardens might have had an apparent warming effect by comparison with the bare, newly cleared military airfield to which the station was moved in early 1941.

All the above historical information emphasises just how much you need to know about the history and surrounding circumstances of local surface weather readings in order to draw any meaningful long-term trend conclusions from them, especially when you are dealing with an apparent global warming trend of only around +0.25°C since 1976. As both you and Vincent Gray have pointed out, the cumulative effect of many changes in location and surrounding circumstances means that you really cannot rely on the surface record to such a high level of accuracy, especially when there is a cogent argument that the majority of factors likely to have affected the record may reasonably be expected to have resulted in a warming bias over the last 3 decades or so.

Regards Ken Parish

Subject: Darwin temperature record
Date: Wed, 29 Mar 2000 12:51:29 +0930
From: "legalnet" <kparish@legalnet.net.au>
To: "John Daly" <daly@vision.net.au>

Dear John,

Further to my emails of earlier today, I have now heard back from Darwin Bureau of Meteorology. The facts are as follows.

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! I am sure that this factor accounts for almost the whole of the observed sudden cooling in 1939-41.

The record after 1941 is accurate, but the record before then has a significant warming bias. The Bureau's senior meterologist Ian Butterworth has written an internally published paper on all the factors affecting the historical Darwin temperature record, and they are going to fax it to me. I could send a copy to you if you are interested.

Regards      Ken Parish

PS As a matter of idle historical interest, it is perhaps fortunate in one sense that the temperature station was moved when it was. The Darwin Post Office suffered a direct hit from a Japanese bomb during the first raid on 19 February 1942. The postmaster Hurtle Bald, his wife and daughter and 7 post office staff members were all killed instantly, and the post office itself was utterly destroyed. The Northern Territory's Parliament House now stands where it once was. Some would wish for a time warp causing the bomb's arrival to be delayed by 58 years!

The whole point of this investigation of just one station is that although Darwin shows an overall cooling due to that site change, this faulty record is the one used by GISS and CRU in their compilation of global mean temperature. More importantly, most of the stations used by them will have similar local faults and anomalies, rendering any averaging of them problematical at best. The best statistical number-crunching cannot eliminate these errors.

And why pick on a cooling station - on a site skeptical of `global warming'?

Simply this - the vast majority of stations are affected by urbanisation with inadequate urban adjustment by GISS, as demonstrated elsewhere on this site. Even where urbanisation is not at issue, rural stations also have serious local problems, discussed in more detail in "What's Wrong with the Surface Record?". (One such station here in Tasmania is also featured on this site - "Hot Air at Low Head")

The net effect is that since most such local errors result in warming (and not cooling as in Darwin's case), the result will be an apparent global warming in the surface record where none may actually exist. This is why the satellite record is a much more reliable guide to recent temperature trends.

Darwin was picked out here simply because it's record was visibly faulty even from the data itself. But if Darwin can `slip through the net', what happens to those thousands of faulty station records where the faults are less visible and obvious? As Ken Parish pointed out above,

"All the above historical information emphasises just how much you need to know about the history and surrounding circumstances of local surface weather readings in order to draw any meaningful long-term trend conclusions from them, especially when you are dealing with an apparent global warming trend of only around +0.25°C since 1976".