No, The Bureau Of Meteorology Is Not Fiddling Its Weather Data

Over the past week or so, the Bureau of Meteorology has stood accused of fudging its temperature data records to emphasise warming, in a series of articles in The Australian. The accusation hinges on the method that the Bureau uses to remove non-climate-related changes in its weather station data, referred to as “data homogenisation”. If true, this would be very serious because these data sets underpin major climate research projects, including deducing how much Australia is warming. But it’s not true.

Joe Raedle/Staff

Lisa Alexander is the Chief Investigator for the ARC Centre of Excellence for Climate System Science and a Senior Lecturer Climate Change Research Centre at UNSW Australia. Andy Pitman is the Director of the ARC Centre of Excellence for Climate System Science at UNSW Australia. Originally published on The Conversation.

Crunching the numbers

Data homogenisation techniques are used to varying degrees by many national weather agencies and climate researchers around the world. Although the World Meteorological Organization has guidelines for data homogenisation, the methods used vary from country to country, and in some cases no data homogenisation is applied.

Homogenisation can be necessary for a range of reasons: sometimes stations move, instruments or reporting practices change, or surrounding trees or buildings at a site are altered. Changes can be sudden or gradual. These can all introduce artificial “jumps” (in either direction) in the resulting temperature records. If left uncorrected, these artifacts could leave the data appearing to show spurious warming or cooling trends.

There are many methods that can be used to detect these “inhomogeneities”, and there are other methods (although much harder to implement) that can adjust the data to make sure it is consistent through time. The Bureau uses such a technique to create its Australian Climate Observations Reference Network – Surface Air Temperature (ACORN-SAT) data set. These data are then used to monitor climate variability and change in Australia, to provide input for the State of the Climate reports, and for other purposes too.

In a statement about its climate records, the Bureau said:

The Bureau measures temperature at nearly 800 sites across Australia, chiefly for the purpose of weather forecasting. The ACORN-SAT is a subset of this network comprising 112 locations that are used for climate analysis. The ACORN-SAT stations have been chosen to maximise both length of record and network coverage across the continent. For several years, all of this data has been made publicly available on the Bureau’s web site.

Complex methods

Australia has played a leading role in developing this type of complex data-adjustment technique. In 2010, the Bureau’s Blair Trewin wrote a comprehensive article on the types of inhomogeneities that are found in land temperature records. As a result the International Surface Temperature Initiative (ISTI) has set up a working group to compare homogenisation methods.

Some of our own research at the ARC Centre of Excellence for Climate System Science has tried, with the help of international colleagues, to assess the impacts that different choices can make when using these different homogenisation methods. Much of our work focuses on temperature extremes. We have studied the impacts on large-scale extreme temperature data of changing station networks, different statistical techniques, homogenised versus non-homogenised data, and other uncertainties that might arise.

Our data on extreme temperature trends show that the warming trend across the whole of Australia looks bigger when you don’t homogenise the data than when you do. For example, the adjusted data set (the lower image below) shows a cooling trend over parts of northwest Australia, which isn’t seen in the raw data.

Trends in the frequency of hot days over Australia – unadjusted data using all temperature stations that have at least 40 years of record available for Australia from the GHCN-Daily data set.

Trends in the frequency of hot days over Australia – adjusted ACORN-SAT data. The period of trend covers 1951-2010 when both datasets have overlapping data. All data used in figures are available from

Far from being a fudge to make warming look more severe than it is, most of the Bureau’s data manipulation has in fact had the effect of reducing the apparent extreme temperature trends across Australia. Cherrypicking weather stations where data have been corrected in a warming direction doesn’t mean the overall picture is wrong.

Data homogenisation is not aimed at producing a predetermined outcome, but rather is an essential process in improving weather data by spotting where temperature records need to be corrected, in either direction. If the Bureau didn’t do it, then we and our fellow climatologists wouldn’t use its data because it would be misleading. What we need are data from which spurious warming or cooling trends have been removed, so that we can see the actual trends.

Marshalling all of the data from the Bureau’s weather stations can be a complicated process, which is why it has been subjected to international peer-review. The Bureau has provided the details of how it is done, despite facing accusations that it has not been open enough.

Valid critiques of data homogenisation techniques are most welcome. But as in all areas of science, from medicine to astronomy, there is only one place that criticisms can legitimately be made. Anyone who thinks they have found fault with the Bureau’s methods should document them thoroughly and reproducibly in the peer-reviewed scientific literature. This allows others to test, evaluate, find errors or produce new methods.

This process has been the basis of all scientific advances in the past couple of centuries and has led to profoundly important advances in knowledge. Abandoning peer-reviewed journals in favour of newspaper articles when adjudicating on scientific methods would be profoundly misguided.

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    Thank you for this article. I read one of the early -The Australian- pieces claiming the world was cooling and homogenization was hiding it, and asked myself why then are ice sheets collapsing? Why are migration patterns changing? Why is the ocean acidifying? etc etc. I was also astonished by the ludicrous comment in the article suggesting the debate was about 'real data' vs computer models. As if computer models are developed using fake data...

    What do you do when one of the major information sources for a country decides to become a source of misinformation? Can they be taken to court?

      And all the idiots who just believe what's in the paper....

      The Australia (an others with the same agenda) disgust me with the major consistency of false reporting they carry out. Its time for a royal commission!

    it might be that i'm blind, but are the two pictures of temperature the same? they both have the same address:

      You're right - the correct URL for the second adjusted data set image is

    The Australian is known to be a bit questionable. It did nearly the same thing with its 'analysis' of plain cigarette packaging which was found to be totally false and misleading by Mediawatch.
    original article:

    Just another case of The Autralian using its influence for political reasons.

    Last edited 01/09/14 10:27 am

      Thanks for posting that mediawatch link: I really enjoyed it.

    shows a cooling trend over parts of northwest Australia

    That lighter coloured area is not cooling, the data is still above .0 meaning that it is still warming just less than everywhere else.

    I can guarantee that if such fudging was going on at BOM there is no chance it would stay a secret. There are too many good people with consciences that would happily stand up for the truth. The fact that there are no whistle-blowers means there is no manipulation of data without a factual basis.

    Don't forget the Australian has an agenda - to side with the Abbot governments shrill climate-change denial stance. It's part and parcel of the chain of you suck my ... pardon me ... I mean you PAT my ... back, I pat yours thing that our current government and the Murdoch press have got going.

      Why would anyone want to suck someone's back? /naivete

    The Australian's "reporting" is borderline propaganda. A lot of people are too stupid and naive to pay any attention to that though and would prefer to absorb a biased opinion rather than scientific data. The BBC itself has refused to give climate skeptics an equal voice because the science is too definitive to justify the negative argument. There is always uncertainty in scientific literature, that's how science works.

    Report your methods, report your findings, report your confidence intervals, report what needs to be studied further.

    Hard to call "homogenization" dropping 1917's temperature.

    "The Bureau measures temperature at nearly 800 sites across Australia, chiefly for the purpose of weather forecasting. The ACORN-SAT is a subset of this network comprising 112 locations that are used for climate analysis"

    so the is best climate changing global warming data set is cherry picked from those 800? how many of those 800 are actually real physical weather stations and not just ex-weather stations whose "output" is actually just a simulation of whats expected Ie: getting hotter all the time (as has been previously been admitted with the world-wide network)

      Though if you look at the images above, which are based on ALL the locations, you'll see they show the same thing. There's no conspiracy here.

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