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Melbourne heat — BoM makes mystery corrections, but misses new skyscrapers. Incompetence?

Posted By Joanne Nova On March 21, 2015 @ 2:57 pm In Global Warming | Comments Disabled

More errors in ACORN -- The Bureau of Met wonder-database corrects for mysterious “statisticals” but not for 15 story buildings built next to the thermometers. They correct a step change that doesn’t occur in minima, but don’t correct for one that does in maxima. Big site changes are marked in some datasets but not in others. And where is the correction for obvious urban heat island effects? Bear in mind, the size of the artificial steps and corrections is on a par with the warming supposedly due to carbon dioxide. Hmmm.

The BoM database needs to be independently and publicly replicated, all the way from their raw data to the final output down to several decimal places. Then we will all know what is going on. Let’s shine a light in. If it ain’t replicated, it ain’t science.

Melbourne has one of the longest temperature records in the Southern Hemisphere. Looking at the original records it appears Melbourne maximums have not changed much from 1855 – 1995. Then they suddenly jumped or stepped up.

Tom Quirk did some sleuthing, and figured out why that happened. But what he can’t figure out is why the Bureau missed this adjustment, yet makes other adjustments no one can explain. At the same time as the temperatures suddenly jump 0.7C, two big skyscrapers were built directly south of the sensors (see the photo below). The tallest is a 15 story block finished in 1997.  Beside it is a shorter tower finished in 1998. The BoM corrects for “statistical” problems, but not for 15 story wind-blocks?

The all-marvellous ACORN is meant to adjust for exactly this kind of site change. Instead, the obvious upward step is left in the ACORN record, but other effects that can’t even be explained get “corrected”. There are step corrections in ACORN that “fix” mysterious attacks of something the BoM calls “statisticals”. But statistics don’t zip around the streets affecting measurements. Why do the original records needed to be changed at all?

Paradoxically, the BoM notes site changes in some data sets but not others about the same site. They correct for these site changes in the minima, even though it’s the maxima that are affected. They say they compensate for the Urban Heat Island effect, but the corrections are step changes when they should be long slow changes, just like the urban heat effect supposedly being countered.

During the time as these huge blocks were being built, the all-marvelous ACORN dataset also tells us that the bureau changed the thermometer from the older thermometer-based station to an automatic, electronic one.  Oddly the raw site record does not mention any instrument change at all. This is just a quality control problem. The BoM call it world’s best practice (we agree, things are sloppy everywhere!).

A new station has been set up 2km away from this old historic one, at “Olympic Park”, where it’s about 1C cooler. It is still very near the centre of the large city of Melbourne, but not next to skyscrapers. This shows a clear 1C urban heat island effect. Presumably if we compared the temperature outside the city and suburbs, it would be much larger than this.

Spot the new wind-blocking buildings to the south and south-East of the thermometers

Melbourne, an old long important record

The Melbourne temperature record is one of the “long time” instrumental records of Australian temperature. It starts in 1855 and continues to the present day. Originally measurements were made in the Flagstaff Gardens. Then when the Melbourne observatory was established in 1863 near the Botanical Gardens, the measurements were taken at that location until 1907 when there was a move to the present location on the corner of Victoria and Latrobe Streets in central Melbourne.

See the step change below in Melbourne’s long term record. It is about of 0.7 +/- 0.2 0C. That step up is larger than the rise from 1855-1995. Note the rise in the minima after 1940, which appears to be mostly the UHI effect. (See below).

Figure 1: Melbourne Regional Office annual average  minimum and maximum temperatures, first measured in the Flagstaff Gardens, then at the Observatory, and then from 1907 at the present site, the corner of Victoria and Latrobe Streets.


These buildings block the southerly wind which brings cool air from the ocean. The BoM corrects for them in the minimums (where they don’t appear to have any effect), but not the maximum temperatures (where they appear to cause the step change).

Figure 7: CityGate tower directly to the south east of the BOM thermometer site in 2015 after the site was closed (see Figure 2)

We can see the urban heat island effect in Melbourne.

A station 20 km away (Laverton) does not show the same continuous increase from 1940 – 1970 in minima, though it may have developed its own urban heat island effect in recent years.

Figure 3: Annual average minimum temperatures for the ACORN-SAT homogenized Melbourne Regional Office measurements, raw minimum temperatures for the Melbourne Regional Office and Laverton.

The biggest Urban Heat Island effect is concrete and asphalt absorbing heat all day and radiating it back at night. As we would expect the maximums are not as affected (see below)

Figure 4: Annual average maximum temperatures for the ACORN-SAT homogenized Melbourne Regional Office measurements, raw maximum temperatures for the Melbourne Regional Office and Laverton

ACORN Adjustments

As Tom notes, the BoM describes the adjustments as “statistical”.

The ACORN-SAT adjustment record (Figure 5) shows only an increase of 0.41 0C to the maximum temperature record starting at 1 Jan 1990. This adjustment is explained as “statistical”. Interestingly the adjustment record shows a break in 1996 for the minimum temperature record and this change is ascribed to a new large apartment building “across the street to the south of the site”.

The site was hit with a wave of “statisticals” several times. Paradoxically, these did not affect the maximum at all during the year the obvious step occurs due to station changes or new wind-blocking buildings.

The BoM tells us that they compensate for UHI (Urban Heat Island). But UHI is a usually a gradual rise, a slope change, rather than a step. Where this happened in Melbourne (over decades) ACORN does a step change, which doesn’t make sense given the gradual increase in concrete and buildings. In the one case where a step change adjustment looks justified, where a thermometer was changed, or buildings slapped up next door, there is no compensation (red line max should show some correction in 1996).

The minimum was adjusted because of the new buildings, but not the maximum.

Figure 5: ACORN-SAT adjustments to the raw Melbourne temperature measurements shown in Figures 2 and 3.


Tom Quirk’s full analysis with graphs and tables as a 750k PDF


Last word: We skeptical scientists think corrections to the originally recorded data should be made for documented reasons, but not for “statistics” alone because they are not a force of nature.

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Raw data: http://www.bom.gov.au/climate/data/index.shtml

Image supplied from Joanne Nova

ACORN-SAT information and data


The wind varies from day to night and from season to season. Wind speed is usually lowest during the night and early hours of the morning before sunrise. It increases during the day as heating of the earth’s surface induces turbulence in the wind stream. Wind also varies, with very localised effects of some weather phenomena such as showers and thunderstorms. Examples of the diurnal variation are the sea breeze, which brings relief on many hot days, and the valley or katabatic breeze, which brings cold air from inland Victoria down valleys during the night and early morning towards Melbourne. These breezes are responsible for winds being more often from the north during winter, particularly during the morning. They are also responsible for winds being more often from the south during summer, particularly during the afternoon. This is in spite of the predominant wind stream being westerly in origin. There is a marked tendency for the very windy days to occur during the late winter and early spring months. Melbourne’s strongest wind gust on record is 120 km/hr on 3 September 1982


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