BoM says re Hobart on 1st April 2014, “..31 degrees Celsius was the hottest April day since records started in 1881.”, but history shows sites nearby experienced several relatively hotter events

The ABC reports – Records melt as Hobart swelters through hottest April day in 132 years
Checking hottest April day statistics at this BoM page – just amend the station number in the URL.
Checking daily data a month at a time in District 94 on Australian Weather News AWN – April 2005 at AWN shows the two hot days on 1st & 2nd.

The article could have been more balanced by pointing out other hotter events in the very small and variable District 94. IMHO Tuesday was just another early April hot day where the peak max happened to fall at central Hobart. I wonder if we should expect more balance from our scientists at the Bureau of Meteorology.
Make anomaly maps for any day you choose at this BoM page.

28 thoughts on “BoM says re Hobart on 1st April 2014, “..31 degrees Celsius was the hottest April day since records started in 1881.”, but history shows sites nearby experienced several relatively hotter events”

  1. 31C is really fantastic, we get thousands of tourists here in Broome during the winter when it drops to around 30c, too cold for me though! We had 37C maximum today.

  2. That’s a bit unbalanced Warwick ..

    What about and Campania, Melton Mobray? Weren’t they worth a mention? Bushy Park, for instance, had a 31.6 against its previous record of 30.6. Annual mean is 18.0

    You slyly chose observation sites that were south of Hobart – even as far as going to a completely different climate regime at Maatsuyker. There is a North to South (actually NNE/SSW) mean maximum temperature gradient across Tasmania in April due to the predominant mean W’ly wind regime. When in a NNW flow regime it makes perfect sense that locations further south would have greater temperature anomalies (compared to the mean) than those further north.

    Sometimes applying a little meteorological common sense goes a long way.

    Try again Warwick!

  3. CAMPANIA (KINCORA) (094212) which had 31.6 degrees on Tuesday 1 April 2014 enjoyed 32 degrees on 2nd April 2005 – more evidence that the 2005 event was more significant than the 1 April 2014 “one day wonder”.
    MELTON MOWBRAY (NORTH STOCKMAN) (094201) which had 30 degrees on Tuesday 1 April 2014 enjoyed 30.2 degrees on 2nd April 2005 – more evidence that the 2005 event was more significant than the 1 April 2014 “one day wonder”.
    And please refrain here from using pejorative terms such as “sly” –
    so far I have only noticed GEEVESTON (CEMETERY ROAD) 94137 in District 94 to join HOBART (ELLERSLIE ROAD) 94029 in enjoying an “all time high” on 1 April 2014. But Geeveston only has data from 1971 whereas Hobart had it previous high on 1 Apr 1941.

  4. Yes but would we have been able to prevent this second pleasant day in Tasmania if thirty years ago we had destroyed all the Western economys and given our wealth to foreign tyrants that hate us.

  5. Putting aside the arguments about record temperatures early in April, as +/- one degree or so is probably not significant being at the beginning of the month heading into Autumn. However what hit me more particularly was in Warwick’s headline: “BoM says … since records started in 1881.” So records prior to 1910 are worth looking at again!!!
    When will they start trotting out pre-1910 data for the rest of the country?

    When we see BoM’s refusal to consider Australian pre-1910 temperature data because Stevenson Screens may not have been used, how is it that many sets of data in other countries start from 1850 and the Central England Temperatures series date from 1659?

  6. Warwick
    Just checked ACORN temps for 1 Apr, 1941 – 31.5C. Since ACORN is the ‘be-all-and-end-all’ as far as temps go, has someone totally stuffed up.
    First we have the BoM using pre-1910 data has Paul mentions above – now we have the OFFICIAL record stating 31.5C happened on that day (0.5C more than 1 Apr, 2014).

    19410401 31.5
    The BoM did the same for Adelaide’s top temp. So sometimes we adjust upwards – but mostly downwards.
    This is on the BoMs Aust Climate summary page which verifies this is the data they use (when it suits apparently).
    Accessing Australia’s climate change datasets
    The Bureau is responsible for collecting, managing and safeguarding Australia’s climate archive. Several homogenised datasets have been developed from this archive to identify, monitor and attribute changes in the Australian climate.
    This statement has been prepared using the homogenised Australian temperature dataset, ACORN-SAT and high-quality rainfall data.

  7. Thank you Ian for checking the ACORN version. It is supposed to be the Rolls Royce of Australian temperature data. You could not invent this tangled web of dubious information.
    Just to test your powers of concentration – here is a graphic for ACORN max minus raw max each day for March and April 1941. How does the BoM know that the weather person in 1941 made an error of only 0.1 degrees on 31 March 1941 but on the next day was so careless as to make an error reading the thermometer 0.9 degrees too cool? Of course the actual 1941 readings would have been in degrees F.

    And here is the same difference for all of 1941 –

    how does the BoM know that only on one day in 1941 – the 23 January the weather person got the reading EXACTLY correct?

  8. Thanks for that, wazsah. I was just checking the raw v ACORN from the BoM data for Hobart. Got this far before giving up at Apr 4th, 1941 – what’s going on?
    Raw ACORN
    30.6 31.5
    22.9 23.7
    14.9 15.6
    16.3 17.2

    Maybe someone should point this out to the BoM. Or maybe not.
    Did the same for Bourke , Jan 39. No ACORN temp matched the raw temp with all temps above 30C being adjusted down and temps below 30C being adjusted up.

  9. I continue to be gobsmacked at the accusations that BOM climate dept ‘fiddle the books .
    Are they so obsessed with AGW to such an extent that they would bend the records to match the Mann AGW hockey stick?
    Such serious accusations!
    If there is corruption.. some one will come clean one day

  10. Hi Warwick

    Lets do this all again – ACORN is for climate change – it takes into account:
    – the replacement of thermometers;
    – changes in observing practices;
    – expansion of the network into remote locations;
    – changes in infrastructure surrounding a weather station;
    – relocation of the weather stations.
    If you don’t like the published peer reviewed mechanisms for establishing cliamte change metrics then you can easily publish a criticism in a peer reviewed paper. People will take notice. If you can;t come up with anything better then maybe there is a hint there.

    Absolute records are help for each station – they are un-adjusted for the above changes. A record is a record. If a city hits a new record, whether it is due to man made urban heat island effects, due to accumulation of carbon dioxide, or due to increased solar activity, then it is a record – no matter what the mechanism. All this is on the Bureau web site – it took me 2 seconds to look this up.

    I know you know all of this Warwick – it disappoints me that you choose to be so mischievous. I’ll copy this text – ready for then next time you conflate ACORNSAT and climate records.


  11. “Absolute records are help for each station” – should be “Absolute records are held for each station”

  12. So George, tell me. In Hobart on 1 April, 1941 was the temperature 30.6C (raw) or 31.5C (ACORN). The Hobart Reg Off has been on the same site since records began, they have used a SS since at least 1910 and I’m sure they would have followed correct procedures (being an official Reg office like Sydney Observatory).
    Has a record been broken or not?
    If the absolute (raw) temp is the ‘real’ temp as far as a record goes (as you imply), why have ACORN temps at all for stations that haven’t moved, etc?

  13. I have just faxed this text to BoM Tasmanian Head Office – Hobart – Note as of 1.30pm the fax has not transmitted. I will try the fax again Monday.
    Dear Officer in Charge,
    I have a blog post commenting on your claim –

    BoM says re Hobart on 1st April 2014, “..31 degrees Celsius was the hottest April day since records started in 1881.”, but history shows sites nearby experienced several relatively hotter events
    We now find that your Rolls Royce temperature time series ACORN for Hobart says there was no record on 1 April 1941.

    You are very welcome to add a comment at the blog – we would be very interested to hear from the BoM some enlightenment re the following three questions –

    [1] Why you did not tell the ABC there were several warm spells in Hobart and District 94 for early April over the last 30 years or so – in particular the 2 days in 2005 which was a more significant warm event.

    [2] You know the BoM regards pre-1910 temperature data as unreliable because of doubts about instrument exposures – yet you quoted a record from 1881 to the ABC when it suited the BoM to promulgate the “hottest April day ever in Hobart” story last week. Is this not inconsistent?

    [3] You could also have explained to the ABC why your ACORN data for 1 April 1941 contradicts your record claim.

    We hope you can set us right.
    Yours etc

  14. ‘If there is corruption.. some one will come clean one day’

    Confirmation bias is sufficient explanation. Which is why any and all ‘adjustments’ to raw data is such a slippery slope.

  15. Ian

    Whilst I work as a scientist, and studied weather at Uni, I’m not a climatologist and the question is well outside my specific area of expertise. However, it seems clear that the observed values (what you call raw) are perfectly correct and reflect the actual temperature in Hobart on 1 April, 1941. As does the value on 1 April, 2014. You can see the observed 1941 values for Hobart here:

    Since 1 April 2014 was hottest it now claims the record as the highest observed value.

    From a climate change perspective, it is a different story. Hobart of 1941 is very different to Hobart of 2014 – no doubt UHI effects are significant effect – and no doubt Warwick would agree. To assess whether the climate is changing items such as UHI need to be taken into account. Warwick would be furious if they assumed that Hobart hadn’t warmed in part due to UHI. I image (guess / think / hypothesize) that early (pre-1960) Hobart values have been lifted upwards to account for UHI. Note that I haven’t explicitly looked and am only hypothesizing.

    ACORN SAT allows for climate comparison and understanding how our climate is changing – and to do this apples need to be compared to apples.

    The Official Climate Record tells us what we’ve experienced in the real world.

    Try not conflate the two – anyone who knowingly does so is being deliberately mischievous..

  16. So George, can you tell me. When temperatures are compared with the past are:
    a. only the adjusted ACORN data used (about 112 stations);
    b. all stations used with only observed temps used;
    c. a mix of both;
    d. or shading between areas using ACORN stations as the designated centres i.e. like GISS NASA.

  17. Ian

    What do you mean “When temperatures are compared with the past”? Are you asking this from a specialist’s perspective wanting to understand if the climate is changing (I would expect it would be ACORN SAT only – A) or from general users perspective asking for typical historical information such as how much rain does Hobart get in winter, what’s the average maximum temperature, what months are windiest, what is the highest temperature that has happened in April, how many days on average does it snow (I would expect it would be the Official Climate Record – B)

    Caveat – ask someone who works in the Bureau in their climate area for an accurate answer – mine is only precise.


  18. George
    Like when the BoM says that 2013 is the hottest year or this is the hottest day (i.e. 7th Jan 2012),
    month, season, etc, What data are they using to compare with previous data to make those claims?
    You say that observed data is the way to go – but the ACORN data is what BoM claim to use – just 114 stations!
    Someone has asked the bureau – no answer has been forthcoming.

  19. Ian part 1: Firstly I don’t know – but the following is my best estimate

    Reporting an average value over a continent or a state is very different from reporting a point value. It is a derived value – assumptions have to be made about how values for mountains, valleys, rivers, lakes, islands and coastal strips will be interpolated from point values. I assume, therefore, that a standardised data set in time and space is better placed to do that interpolation and produce a space averaged derived value.

    Ian part 2: I have no idea.

    I’d guess either a problem was identified in a data source – or additional data was reported – or processing strategies were reviewed – and that led to a slight decrease. Have you written to them and asked?


  20. Noticed a comment in a forum regarding the Sydney observatoryhill site for your info’

    quote from ‘steve 777’
    Things seem to have changed at Observatory Hill. Instead of recording rain when it doesn’t, it now seems to be the only site in the Sydney area to record no rain so far this month. There are some missing data from early this week. Is the site malfunctioning?

  21. George,
    What I can’t get my head around is that the recent temps don’t seem to have been adjusted at all. I quickly checked the raw v ACORN data for Jan 2013 for Hobart (where there was a 41.8C) and no change. So will this be adjusted at a later date to ‘homogenise’ it properly for a weighted average?

    Maybe the change to 1988/2009 may have come about because of ACORN when introduced in 2012.

    By the way, I have sent questions to the BoM but only received answers from our local office.

  22. Hi Ian

    I can’t answer that for you – but I occasionally have reason to liaise with people in the Bureau – so if I remember I’ll ask your question.

    Talking about people in the Bureau – it does surprise me that there is this perception that there is a grand conspiracy within government organisations to unreasonable promote climate change / climate warming. The people I deal with seem to be as hard working and honest as people in other professional businesses that I interact with – with the one caveat that they tend not to be risk takers. To me they seem to be rational and deliberate decision makers. If I sometimes get defensive in this forum it is because what I see within that organisation doesn’t map to some of the apparently baseless allegations that are made.


  23. I’m sure they are all hard-working and pleasant people, George. It’s the data and the way it has been homogenised. Within 12 months of ACORN being introduced we suddenly had the hottest day, month, season and year on record – yet Oodnadatta’s record of 50.7C in 1960 was untouched and the longest heatwave (in Marble Bar, 1923-24) remains intact. I know that that’s not indicative, but you would think they might have been beaten with the type of comments the heads of the BoM have made.
    As some commentators have pointed out, the satellite data doesn’t support the claims made about 2013 (and yes, I realise RSS etc don’t take ground temps). It may not be a conspiracy, it may be the process that needs revisiting. They obviously did with the 1998/2009 data.

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