Sydney's historic weather station: 150 meters makes all the difference

Here is an interesting story about the weather station in Sydney at the Astronomical Observatory (well sort of, it got bumped off). It seems the astronomers and meteorologists at the observatory got into a tug of war in 1912 over a cottage and the resulting move in 1917 ended up skewing the entire temperature record irreparably. First, here is a photo of what the observatory and grounds looked like “back in the day”. While I can’t be certain, the latticed canopy at the left may be where they had the early thermometer exposure. Early attempts at sheltering the thermometer from sunlight were often large affairs like this. It may also simply be a lounge area, but the design doesn’t look relevant for that.

Photo circa 1874, more photos and history here

Now here is the article of interest from The Sydney Morning Herald:

How hot heads caused climate change

Richard Macey

July 2, 2008

NINETY years ago Sydney’s temperature took a leap. However, it had more to do with rising political, rather than global, heat.

The instant climate change was remembered yesterday as Bureau of Meteorology staff, and astronomers, gathered on Observatory Hill to mark 150 years of Sydney’s weather observations.

On July 1, 1858, NSW’s government astronomer, Reverend William Scott, noted 12.7 millimetres of rain had fallen in the previous 24 hours. “He was the astronomer, the timekeeper and the meteorologist,” the current astronomer, Nick Lomb, recalled yesterday.

In 1908 the role of recording rainfall and temperatures was taken over by the Commonwealth’s new Bureau of Meteorology, which was allowed to share accommodation in the observatory’s grounds.

However, Dr Lomb said, it was a tense relationship. William Cooke, appointed in 1912 as the new astronomer, wanted the bureau out so he could move his family into the observatory’s occupied residence. “A battle between the two sides” ensued.

The astronomer triumphed and in 1917 the bureau was moved 150 metres south, to an old cottage across the hill.

The seemingly insignificant shift triggered a sudden spike in Sydney’s temperature records.

A 1972 study by meteorologists Rosea Kemp and John Armstrong found that since 1918 Sydney’s average annual maximum temperature, as recorded at the new site, was 0.7 degrees warmer than the average at the old site. Winter averages were up 1.6 degrees.

Dave Williams, a senior bureau meteorologist, said the new site was sheltered from cold winds by buildings, creating a micro-climate. “It’s quite noticeable in the winter months,” he said.

While some of the increase probably resulted from warming caused by Sydney’s urban development, the artificial spike has meant Observatory Hill’s statistics cannot be included in climate change studies.

In 1989 a young bureau observer, Mike De Salis, inherited the job of making daily visits to collect rain and temperature readings. On cold, wet days it could be a miserable task. “The worst part was trying to measure the rainfall accurately, within 0.2 of a millimetre, while it was pouring rain,” Mr De Salis said.

For yesterday’s 150th anniversary, Mr De Salis returned to again make the manual observations. The rain gauge had detected just 0.2 millimetres.

An exhibition of meteorology equipment opened yesterday at the observatory.

(h/t Barry Hearn)

I’ve located the station on Google Earth. I’ve posted three annotated views below but you can also locate it here at this live link.

First the wide view with the Google Earth measuring tool showing the distance from the Astronomical Observatory. Note the depression in the earth and the proximity of the freeway toll plaza.

Click for larger image

Now here’s a closer view showing the complex of buildings mentioned in the article. The Stevenson screen with the thermometer is in a small yard on the right side of the complex, closest to the freeway:

Click for a larger image

 And finally the close-up view where I measure the distance to the asphalt cul de sac to the screen, not also the concrete walkway:

Click for a larger image

Based on distance to artificial heat sources such as the asphalt and buildings, this station would rate a CRN4, and could be argued to be a CRN5 due to proximity to the walkway, which appears to be concrete, but I can’t verify that from these photos.

As mentioned in the article, the Australian Bureau of Meteorology wisely chose to exclude this station from “climatic studies”.

However that doesn’t stop Dr. James Hansen of NASA GISS from using it, as it is in fact part of his GISTEMP database, see the plot below from GISS:

See the source plot and data here at NASA GISTEMP database. Note the lat/lon matches that of the lat/lon labels in lower left of the Google Earth images I posted above.

It makes me wonder; if the station is not good enough for BoM to use, why would GISS use it?