Monday, 24 August 2015

How does the Australian Bureau of Meteorology ACORN-SAT data compare to its source?


In previous posts I’ve examined the Australian Bureau of Meteorology’s temperature records.

In this article, I examine the Bureau’s practice of ignoring data prior to 1910. I also look at the adjustments the Bureau has made to the original data. ACORN-SAT is the adjusted temperature record. CDO is, supposedly, the ‘raw’ data.

Here’s a few samples from the full article:

This graph shows all of the weather stations used by the BOM for ACORN-SAT but with the pre-1910 data included.

Two things stand out:

1. There was rapid warming from 1860 to 1900, much more than the little bit of warming seen since 1900.

2. 1900 was the hottest year since records started in 1860.

ACORN_CDO temperatures

The adjustments make the period 1910 – 1950 appear colder.

BOM ACORN Adjustments

There is nothing special about the years 2013 and 2014. I’ve shown four decimal places on the temperatures. In reality, we’d be lucky to measure to the nearest degree. So in 1900, the average maximum temperature was 27 degrees Celsius. In all the other years, the maximum average temperature was 26 degrees Celsius. No big deal.

BOM ACORN average maximum temperaturess

Unfortunately, I’m lead to the following conclusions:

1. The year 1900 is likely to have been the warmest on record.

2. The rate of warming from 1860 to 1910 it much larger that any warming experienced in the recent past.

3. There was a systematic downward adjustment of temperature records prior to 1950. This makes more recent temperatures appear warmer by comparison.

It’s may be coincidental that both the decisions to eliminate pre-1910 data and to systematically adjust pre-1950 temperatures downward, support the hypothesis of human-induced global warming.

If it is a coincidence, it’s a mighty big one.

Click here to download the PDF

1 comment:

  1. Fascinating stuff. I have done a similar exercise using the Berkely Earth dataset for the 112 Acorn sites.
    Just one thing, you don't mention the issues with 19th and early century data due to the lack of effecting shielding from the elements via a Stevenson screen. These usually, depending on the location, make the temperature readings too high. You can usually check for this issue by comparing average annual sunshine and/ or cloud cover hours with the change in maximum tenperature from pre to post about 1910. You often find this temperature change correlates with the amount of sunshine at that location.for that time of the year. For instance in southern Australia the greatest temperature diffference pre and post 1910 is primarily in the summer and least in the winter when the likelihood of cloud cover is greatest. This check of course is less effective if the cloud cover is fairly constant throughout the year.

    The unreliability of the pre 1910 data is due primarily to the exposure to the sun and this is why the BoM only uses data from 1910 . By then most of the relevant sites had Stevenson screens.


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