Perth temperature history
Guest post by Chris Gillham
It’s worth digging a bit deeper into claims by the Bureau of Meteorology that Perth endured its equal hottest summer in 2010/11 and its hottest first four months of the year on record.
On May 2, 2011, The West Australian newspaper published the following story, claiming that “Perth has experienced its hottest start to the year on record, with a mean maximum temperature of 31.5C for the first four months, breaking the previous record of 31.3C set in 1978”.
Oh dear, Tim Flannery was right and Perth really is at the forefront of global warming.
But can we trust the BoM calculations? Was the mean maximum in the first four months of 2011 really 31.5C?
Well, we can do it the BoM way and calculate the average of the rounded monthly figures for January (32.5C), February (34.1C), March (31.9C) and April (27.3C). Yep, that’s an average 31.45C, which further rounds out to 31.5C. Too easy.
But what if we don’t average the rounded monthly figures and instead average the actual maximum temperatures recorded on each day during the first four months? It’s pretty easy to do. Just check the monthly figures for Perth Metro (station 9225), which is the official “Perth” site for the BoM, for January, February, March and April 2011.
The actual maximum temperatures in all 120 days of January, February, March and April 2011 can be seen here. Get your spreadsheets busy and figure out the average maximum. You’ll find it’s 31.42, which rounds to 31.4C.
So the actual mean maximum for Perth in the first four months of 2011 was 31.4C, not 31.5C as claimed by the BoM.
On March 3, 2011, the BoM claimed that Perth’s 2010/11 summer was the equal hottest on record with a mean maximum of 32C. But if you use the daily temperatures instead of the rounded monthly figures, the average summer maximum was actually 31.89C, or 31.9C when rounded. Again, their calculations were based on an average of the rounded monthly maxima rather than the days themselves (see Was Perth’s summer of 2010/2011 a record?).
2010/11 was the third hottest summer recorded in Perth, but not the equal record.
Temperature station location
Ah, but this is being a bit pedantic, is it not, since the first four months of 2011 were still the hottest on record?
That depends upon whether you also want to research a bit deeper into the record itself. The BoM references its official “Perth” temperatures from station 9225 in Mt Lawley, which opened and recorded its first annual temperature means in 1994 – picture below in May 2011 courtesy Stephen Harper.
However, the BoM quotes the previous hottest first four months from 1978. So where was this location?
Before 2004, the official Perth temperatures were recorded at Perth Regional Office (station 9034). Check the first four months of 1978 and the mean maximum was 31.3C, the previous record as stated by the BoM.
Stations 9034 and 9225 are about four kilometres apart and the evidence suggests the Mt Lawley site is slightly hotter during the day than the Perth Regional Office site. Site 9034, which opened in 1876 and closed in 1992, has a 19 metre elevation.
Site 9225, which has had a stable mean temperature since opening in 1993, has an elevation of 25 metres. Proximity to broad river waters and the UHI influence of inner city and university development are probably relevant.
Below are the average annual maxima of station 9034 from 1975 until 1992, bleeding into station 9225 from 1994:
24C
24.6C
24.6C
25.2C
23.9C
23.7C
23.5C
23.8C
24.5C
23.5C
24.5C
23.2C
24.3C
24.8C
24.2C
23.7C
24.3C
1992/93 n/a as switch made from 9034 to 9225 below
24.9C
24.2C
24.5C
24.5C
24.5C
24.9C
24.5C
24.2C
24.5C
24.5C
24.5C
23.5C
24.8C
24.4C
24.6C
25C
25.3C
The average annual maximum at Perth Metro over 17 years is about .4C warmer than it was earlier at Perth Regional Office. If you suspect the increase is because of global warming, not the four kilometre change in location, consider the annual minima in “Perth” from 1975 to 2010:
13.9C
14.5C
14.5C
14.7C
14C
14.1C
13.9C
14C
14.8C
13.9C
14.6C
13.7C
14.2C
14.9C
14C
13.7C
14.3C
1992/93 n/a as switch made from 9034 to 9225
12.9C
12.8C
13C
12.5C
12.6C
13.1C
12.9C
11.9C
12.7C
12.8C
12.6C
12.3C
12.3C
12.5C
12.3C
12.7C
12.4C
The average annual minimum at 9225 over the past 17 years was about 1.6C cooler than it had been at 9034, the drop happening immediately the station change was made. Maybe a rapid onset of global cooling, but a more robust explanation is that the four kilometre change in station locations significantly affected temperature recordings and made historic pre-1994 comparisons dubious at best and irrelevant at worst.
The temperature record at Perth Regional Office
Perth Regional Office (9034) started recording from 1897 and finished in 1992. This location was originally known as the Observatory and started recording temperatures in 1897 at the Mt Eliza site now mostly occupied by Dumas House, adjacent to Kings Park. Although the BoM gives no clues that Perth Regional Office has a history of more than one location, station 9034 is the benchmark for historic temperature comparisons in the capital of Perth.
View of Observatory grounds soon after completion with Fraser Avenue and Kings Park in the background. The meteorological instruments including a Stevenson Screen can be seen in the right of the photograph.
Most of the Observatory was knocked down in 1967 to make way for Dumas House, and at that time the Commonwealth transferred its meteorological instruments to Wellington St in East Perth – about two kilometres away. (Source: Perth Observatory History)
The Bureau of Meteorology Perth Regional Office at 127 Wellington St, East Perth, facing north with the instrument enclosure in the foreground
The elevation changed from about 61 metres at the Observatory to 19 metres in Wellington St …
… and look what happened to the temperatures recorded for Perth Regional Office (9034) …
The trend is a bit more obvious just looking at the mean temp for Perth Regional Office …
It should be noted that in 1963, Perth Regional Office was moved about 300 metres to the east of the Old Hale School building, also atop Mt Eliza (Source: Perth’s Observing Sites)
And for Perth’s temperature record from 1897 to 2010 …
So Perth Regional Office changed its physical location in 1963 and again in 1967, when it moved about two kilometres east into the central city, closer to the river both in distance and elevation but separated by blocks of large buildings, and Perth’s temperatures increased thereafter.
To further illustrate the distortion caused by moving the Stevenson screen temperature recording instrument a few kilometres from its original location, the Mt Lawley 9225 temperatures four kilometres inland show higher maxima and significantly lower minima.
Based on the temperatures charted above, the last two decades in Perth have had the hottest days and coldest nights since records began in 1897. Why are records claimed for average maxima but minima and mean are ignored, and why are any of them relevant for comparison with other locations before 1994?
It’s worth looking at Results of Meteorological Observations Made in Western Australia During 1908 (PDF 29mb) published in 1912 by Commonwealth Meteorologist Henry Hunt:
Well, until 1967 anyway.
Perth Gardens temperature overlap
Perth Gardens was Perth’s first temperature recording location as of 1876, situated about 1.5 kilometres from the Observatory site on Mt Eliza in an area since renamed as the Supreme Court Gardens (see map above).
The 1912 Hunt document also contains a table with monthly and annual mean temperature readings at Perth Observatory from 1897 to 1907, and at Perth Gardens from 1876 to 1907, which provides a useful 11 year overlap.
The 11 year mean from 1897 to 1907 at Perth Observatory atop Mt Eliza is 63.9F (17.72C) and the same 11 year mean at Perth Gardens is 64.9F (18.27C). That’s almost 0.6C difference in the same city in the same weather in the same years. The Perth Gardens did not record temperatures from a Stevenson Screen and this may have artificially increased the temperatures, but Commonwealth Meteorologist Henry Hunt suggests the thermometer was well shaded:
The mean temps for Perth Regional Office from 1897 to 1907 (go to BoM Climate Data and look up min/max for station 9034) are exactly the same as the mean temps for the Observatory in the 1912 Hunt document. These identical temperatures confirm that Perth Observatory on Mt Eliza was the original location for Perth Regional Office temps in its early years starting 1897.
Conclusion
When informing the public that record high temperatures have been experienced, the Bureau of Meteorology should ensure the accuracy of its figures by averaging daily temperatures instead of rounded monthly calculations.
Rounded averages of rounded averages are not accurate and a .1C error is significant if claiming record temperatures, particularly when Australia’s economic and political future is likely to be determined by a public understanding of the need or otherwise for a carbon dioxide tax.
The BoM should also acknowledge that temperatures recorded at its Mt Lawley 9225 station are being compared with stations in different locations where local environmental factors have a significant influence on Stevenson screen thermometers.
Perth’s temperature history is too disjointed to make meaningful comparisons and present-day recordings at Mt Lawley should only be compared to recordings from the same site beginning in 1994.
It might mean Perth has a very short history of temperature recordings, but at least the data will be relevant.
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Chris Gillahm is a 50 year old print/electronic journalist based in Perth who also does graphics, writes html, takes photographs, etc. His interest in the climate change issue stems from the fact that he was university-trained as a journalist to do old-fashioned research and not rely on the accuracy of government media statements. Digging such as this almost always reveals the public only gets half the facts about issues such as climate change. Visit his website here: http://www.waclimate.net/
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When I was born in Australia it was something like 110F? in the shade and my mother put me in a bath of water, which being rapidly cooled was extremely cold which apparently made me rather unhappy. And it just so happened that as I was being dumped in freezing water,the same time the UK experienced one of its coldest winters.
And what do we find now: the UK has just experienced one of its coldest winters, and Australians are being dumped in the cold water of carbon taxes because of the “unprecedented” heat!
Hottest summer, by a fraction of a degree. What does that really mean? If you read the newspaper story, That implies that everything is wilting and dropping dead, when it really means that a person literally wouldn’t be able to tell the difference…especially if they walked between the two temperature stations. Either case is basically picking fly sh*t out of black pepper, creating alarm over a tiny bit of difference.
As much as it is good to pay attention to siting as regards absolute temperature values, if you plotted this in kelvin, the trend is flat. The difference between warmists and skepticas is that warmists like to place significance on nearly immeasurable differences, wheras skeptics just shrug.
We are still within ‘normal’ ranges.
Isn’t averaging averages one of the things you learn NOT to do at an early stage? It can lead to all sorts of errors, mistakes and misconceptions.
Isn’t that what they did with the numbers lead them selves up the garden path by averaging the averages?
Outstanding research. Your head must have been exploding when you discovered the details of that historical record.
You’ve put together into an overwhelming case. How will they dodge this?
Rather good timing too.
Very detailed investigation Chris.
Mt Lawley station resembles a football field size square of dry brown dirt. Is that what all of Perth is like? If not, no wonder it is now reading higher maximums and also lower minimums. If I remember right dry plowed fields will do the same, great absorbers in the day (heating) are also great emitters at night (cooling) leading to higher diurnal range.
I am impressed that Chris has done the basic research for this article that all those who call themselves journalists should but few ever do. It’s not exactly a surprise that the changes in Perth during the last century as the city developed render the ‘historical record’ a nonsense, equally unsurprising that the BOM uses the muddled history and silly maths to claim the most recent summer in Perth “Hottest evah, Sport!” The BOM is another organisation that resists embracing openness and honesty in it’s ‘scientific’ practices and resists FOI requests with the thinnest of excuses.
Great work. Now, can we make BoM acknowledge their flaws in print?
Nice work. Thanks.
The Mt Eliza site is at the top of a big hill (by Perth standards), the press cutting shows 200ft. Wellington St is close to sea level. In the summer, when the afternoon SW sea breeze comes in, the wind fairly whips off the river into the city area. Mt Eliza is well sheltered from that by Kings Park.
Mt Lawley would be the most “typical” site for suburban Perth, but all three are geographically distinct.
Which only goes to reinforce my assertion that global temperature measurement is not only difficult to measure correctly but really not a significant measure of human input into the climate mix of drivers. The only real human input seems to be changing the station positions and fudging the data to fit the output of the models upon which reliance is everything to some.
W.S. Churchill is reputed to have said,”there are lies, damned lies, & statistics!”. It’s is amazing what one can do with numbers, & it would appear that our Colonial Cousins in Australia’s BOM are having some fun. I always wonder what the Global Average Tempreature really means in practice. Some areas experience warmer than usual weather patterns, other areas experience cooler than usual weather patterns, simples. Ooooops! Better be careful I was begining to sound like a highly accurate computer generated Wet Office climate prediction in the year 2100!!!!:-))
Great post Chris. it’s very exciting to see my old home town represented in such an international forum.
To be honest though, I don’t see anything too suspect, other than the usual specious claims of ‘hottest summer on record’. Since the records don’t go back very far, and since the warming trend was already in evidence, it is not really a big deal. If you look on the temperature anomalies map, the whole of the West coast of Australia is considerably warmer than usual compared to the rest of the world that is considerably cooler than usual. I tried to find some kind of link between La Nina and Perth’s weather but couldn’t. I suspected that the effect of La Nina is to cause particularly hot dry conditions for the West coast of australia.
I regularly go home to Oz and I have noted that summers in the earlier part of the decade were disappointingly cool, which show up on the graph. My memory of growing up is that March in particular was extremely hot. I do understand though, the recent summer was very unpleasant.
But you raise, inadvertently, another interesting issue which is to do with the way average, or mean temperature is calculated. My understanding is that the maximum and minimum temperatures are simply taken, but that says nothing about the mean day time and mean night time temperatures. In Perth at least, that would be highly dependant on the sea breeze. If the sea breeze does not come in, as is often the way in March, the temperature can stay high most of the day, but not necessarily as high as it can get by 11am-12pm before it kicks in in January or February.
Simply averaging the Max and Min temperatures can lead to a misleading result.
Hello, folks. I forgot to add, an interesting little piece on last night’s BBC1 magazine show, The One Show, on Sir William Ramsey, a British chemist who eventually discovered neon. This apparently came about because he had analysed natural nitrogen in the atmosphere & found it to be different from the nitrogen produced by chemical reactions, even though that difference was only 1/10th of one percent!!!! Now, where have I heard that a change of 1/10th of one percent can’t make a difference? TSI perhaps? Funny things, numbers!
You got to love the way the warmists will pluck just any random set of data out of the air and then proclaim a record.
We should be going along with it and saying “oh look, its 0.3Celsius warmer than it was 30 years ago. No need to rush is there?”. At that rate, even it it was based on any kind of realistic comparison, we’d run out of fossil fuels long before we had to worry about climate change.
You can get the daily data for Mt Lawley from here. It is station 94608. For some reason it’s in Fahrenheit. But by averaging daily max I get, yes, 31.4C for the first 4 months of 2011. And 30.2C for the first 4 months of 1978.
I actually remember the summer of 1978 – I was there. It sure was hot, with a late blast from Cyclone Alby – but apparently not as hot as 2011.
As one moves inland from the coast, the max is going to get warmer and the min is going to get colder. What is so special is that people still go to the beach to escape the inland heat during a hot summer day.
Nick Stokes says:
May 19, 2011 at 2:42 am
You can get the daily data for Mt Lawley from here. It is station 94608. For some reason it’s in Fahrenheit. But by averaging daily max I get, yes, 31.4C for the first 4 months of 2011. And 30.2C for the first 4 months of 1978.
—-
Interesting. So merely the Celsius to Fahrenheit conversion is also raising the temperatures by rounding.
That is real interesting. Now convert back to Celsius from NCDC numbers then average, does it go back down, stay level, or another step up?
I’ve lived in Perth for 39 years. I think this is the first time anyone has considered the move in the “official” weather site from East Perth to Mount Lawley. Rainfall as well as temperature is measured at the official site. However rainfall in Perth is very localised and the 4Km move is very likely to have a significant effect on the rainfall reading for Perth. I don’t think parallel readings for temperature or rainfall were compared for say 2-3 years after the move although it is apparent such comparisons would have been highly desirable from a scientific point of view. Perth, which is very isolated, has about 10 continually monitored weather sites dotted around the metropolitan area. A better record of temperature and rainfall would be gained by considering the results from all of these sites and obtaining composite results that reflect the temperature experienced (and rainfall occurring) over the entire metropolitan area. Will this occur? Unlikely.
Regardless of whether it holds the record or not, it is an absolute impossibility that any person could objectively (or subjectively) tell the difference of a monthly average of 0.5 degrees.
So the alarmist newspaper stories may interview people who ‘know’ it is getting hotter, but plainly they are talking out their downward facing hole.
Every year it gets hot in summer and the media finds some nitwit sweltering on the beach that says ‘it gets hotter every year’. No, pea-brained-vox-pop commentator, you subconciously absorb dross from the alarmist media and think it is getting hotter.
@wayne
“Mt Lawley station resembles a football field size square of dry brown dirt. Is that what all of Perth is like?”
Pretty much. The climate is Mediterranean. Perth itself is on a coastal sand plain. During the last glacial the coastal plain very dry and was an active dune field. Now it is wetter, and the dunes have been stabilised by scrubby vegetation. Eucalypts and banksias, mainly. “Sandy” is the word.
@Agnostic
It’s more to do with the Indian Ocean Dipole than ENSO. I can’t find much in the way of meaningful information, but I believe there is a decadal trend towards increasing dryness. It needs more research: send me money 😉
Perth summers are hot. I was there (without aircon) for the max max, 46.8C iirc, in about 1990. It was hot.
@wayne
No Perth does not look like this. I took the photograph of the Mount Lawley station a few days ago. All around was green – but reticulation was being used. However, the plot of land on which the station stands is particularly arid. It surprised me how barren it was. Perhaps there is a herbicide regime in place to keep down any vegetation. This summer was a hot one – so any growth which might otherwise have been around the gauge had little chance of surviving without the relief of shade. I do wonder if there is a feeback mechanism in play here. It is hot, so the vegetation dies back. This exposes more sand. The sand heats up and hey presto! the temperature (reading) rises yet further.
On another point: the 2010/11 Perth summer did not have a single day over 40 degrees C as I recall. Just lots of days consistently over 30 degrees C. So it was a different kind of hot summer to the usual. This may indicate the effect a one-off weather event (a particularly warm Indian Ocean off the coast of Perth this year) more than it indicates that our usual summers are becoming hotter.
Interesting. Very good work.
Suggests that a significant rise in temps is nothing more than siting issues and a step change associated with the re-siting. I really have little faith in the cogency of the official temperature records and the validity of the adjustments made to them. And from this ‘corrupted’ (perhaps I should say bastardized) data we are supposed to draw the conclusion that the world is warming by miniscule (but yet said to be significant) amounts such that we should spend trillions of dollars addressing the issue.
I suggest that we get the raw data straight before we draw any conclusions still less spend trillions on what is likely to be a non proble.
Journalist, or detective? Nice work, Chris. Many thanks.
Apparently 1978 was notable year, climate-wise, at two (almost) antipodal points of the globe: http://en.wikipedia.org/wiki/Great_Blizzard_of_1978
Great work Chris. The BOM’s alarmist agenda exposed once more and what an opportune time to see their feet held to the fire.
Richard Verney is right. Perth itself is quite pretty, and very much a garden city. If (big if) you add enough water, you can grow just about anything. Without irrigation, you get bare sand and scrub.