Australia’s weird winter

maxdec200908Guest post by Blair Trewin. Blair is a senior climatologist at the Bureau of Meteorology’s National Climate Centre. He recently took the lead in writing the Special Climate Statement, Exceptional winter heat over large parts of Australia, issued 26th August 2009, updated 1st September 2009.

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Australia has just experienced an exceptionally warm August. Almost the entire country experienced above-average temperatures during the month, but the warmth was most extraordinary in the subtropics. Over most of the southern Northern Territory and the southern half of Queensland (away from the coast), maximum temperatures for August were more than 5°C above the long-term average. Maximum temperatures were the highest on record for August over 49% of Australia.

Averaged over Australia as a whole, maximum temperatures were 3.20°C above the long-term August average, and daily mean temperatures (day and night combined) were 2.47°C above average. Both values are the highest on record for August by close to a degree. In terms of how far the month was above normal, the maximum temperatures in August 2009 are also the highest on record for any month, breaking the record of +3.11°C set in April 2005; the daily mean temperatures rank second behind April 2005.

tmaxanom200908The month was marked by some individual days which were exceptionally hot for August, especially in northern NSW and Queensland. State records were set for August in both states (37.8°C at Mungindi and 38.5°C at Bedourie respectively). Perhaps more exceptional were the margins by which some records were broken, and the number of days on which previous records were exceeded. Collarenebri broke its pre-2009 August record by 5.4°C, and numerous other locations, including Murwillumbah, Moree, Gatton, Miles and Taroom, broke August records by 4°C or more. Such margins are not unheard of at exposed coastal sites – where everything has to go right to achieve an extreme high temperature (not only having a very hot air mass, but having the wind in the right direction to prevent conditions being moderated by sea breezes) – but are virtually unknown at inland locations.

Many locations exceeded pre-2009 August records on five or more days. An especially striking example was Windorah in western Queensland, which prior to 2009 had never reached 35°C in August. In 2009 it happened seven times, and their August record was lifted six times, eventually peaking at 38.0°C on the 29th.

The extremely warm August combined with generally above-average (but not record-breaking) temperatures in June and July to give record or near-record winter temperatures in many areas. Australian daily mean temperatures for winter (1.33°C above average) fell just 0.01°C short of the 1996 record, and maximum temperatures surpassed the record set in 2002. NSW, Victoria and South Australia all had their warmest winters on record, which may come as a surprise to residents of the latter two states, in a season which was distinguished more by an almost complete absence of significant cold than by any major warm extremes.

In terms of weather systems, the month was marked by a persistent high-pressure ridge over the subtropics, preventing cooler air from penetrating from the south into central and northern Australia (until the last two days of the month, by which time it was too late to make much difference). Pressures were also well below normal south of Australia, resulting in very strong and persistent westerlies south of Australia (which made it an extremely wet month in Tasmania). An interesting comparison exists with October 1988, which had very similar pressure patterns, and was also dry over the mainland and very wet in Tasmania. In October 1988 Australian mean temperatures were 2.16°C above average, which was a record at the time (it now ranks fourth). The difference of 0.31°C between the two months is close to the size of the warming trend over Australia in that 21-year period, and suggests that the long-term background warming trend is playing a role in increasing the frequency of high temperature extremes of the type seen in August 2009.

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27 Comments

  1. Weird indeed. In January 2009 Tasmania recorded highest ever temperatures around 41C. Yet horticulturalists complained of an unusually cool summer with frosts that led to failures of crops like tomatoes, pumpkin and corn. Winter (June, July, August) saw record rainfall at some weather stations. However there was little sea level snow which usually fell above 700 metres ie the snow line seems to be rising. I would guess that some hydro catchment areas will record 3 metres (10 feet or 120 inches for the non-metric) even if spring rain is light.

    Record rain and record heat and 2009 is over yet.

  2. Warm winter.
    And continued warmth – crop yields affected?
    I read somewhere yesterday (Grist maybe) that continuing persistant warmth will lower yields (and hopefully necessitate/effect evolution in plant behaviour/growth as they detect new conditions).

    I am seeing noticeable difference in snowlines (I snowboard a lot).

    Marginal resorts are in big trouble (I think 1 deg = 150 m snow level rise according to IPCC AR4) – apart from outlier storms, Buller and Baw Baw will be in strife.

    tim
    heresysnowboarding.com/blog

  3. I’m a cylist with a 37km morning commute and all winter save for a couple of days I’ve been heading into a north wind. Of head-winds, am sick, yes.

    As Kath and Km would say: “Unusual.” “Different.” “Yes, unusual.” (Both) “Hmmmmm!”

    Waiting until the end of September when the blocking sub-tropical ridge breaks up.

  4. Is it weather or climate?

    It was the highest August by over a degree, so more than a degree warmer than last year. Considering Co2 should have warmed us up by something more like 0.02 degrees since last year, there has to be some weather involved.

    And although its not hard to imagine August 2009 beating the last 10 or 20 years all by a degree, it seems much less likely that it would have beaten every year in the last century or so by a degree, unless it had some helping hand from climate change.

    I believe that the only way such an extreme record could have been set is for climate and weather to both be acting together.

    Impact of El Nino cycle surely contributed to this. Australia is usually warmer in an El Nino which should contribute to the strength of the sub tropical high blocking colder southerly air. Unusual about this El Nino is that the waters north of Australia were above average warmth through August, whereas usually they would be cooler than average, so a fair bit of ocean warmth above what is typical for this stage of an El Nino. This ocean warmth could be GW, or it could be some other variation.

  5. NA #1: “Is this data as ‘bad’ as it seems? Is this climate or weather? What is the impact (if any) of the current El Niño / La Niña cycle?”

    It’s weather + climate, as noted in the comment above and the main piece. The El Nino no doubt is having an effect. But it seems about 0.3C hotter than a previous event of this nature back in the late 80s. That extra is probably the global warming signal:

    “An interesting comparison exists with October 1988, which had very similar pressure patterns, and was also dry over the mainland and very wet in Tasmania. In October 1988 Australian mean temperatures were 2.16°C above average, which was a record at the time (it now ranks fourth). The difference of 0.31°C between the two months is close to the size of the warming trend over Australia in that 21-year period, and suggests that the long-term background warming trend is playing a role in increasing the frequency of high temperature extremes of the type seen in August 2009.”

  6. There seems to be a greater prevalence of ‘highest ever’ temperature records over ‘lowest ever’. If this is the case then it would seem to demonstrate that there is more than just weather involved.

    Is there a comparative record of such extremes available – for Australia, the Globe? (I came across the fact that Vidin, in Bulgaria, had its hottest ever in June:-)

  7. When it comes to weather we have conveniently short memories.
    Also the BoM records of some of these country towns only went back to the 1970s whereas they have been settled for at least a century before that.
    I seem to recall that the ski season started about 6 weeks early this year and an all-time cold record was established north of the tropic of capricorn. I can’t find that story but someone may know of it.
    In spite of a few days of local warm August weather there must have been some chill around somewhere.

    http://wattsupwiththat.com/2009/09/04/uah-global-temperature-down-in-august-181%c2%b0c-sh-sees-biggest-drop-of-0-4%c2%b0c/

  8. You’re absolutely correct Spangled Drongo. Here in Yeppoon (Central Qld and just north of the Tropic)we endured the coldest ever recorded June Minimum. In March we had the ‘hottest ever’ by more than 2°…… but records only go back to the 1980s.

    However, I do have the perception that hot records are broken more frequently than cold records. If this is the case then it seems, at least intuitively, to provide evidence of CLIMATE warming.

    But is it only a perception? Is there any evidence?

  9. #11 The snow season experienced perhaps its biggest weeks fall in late April…but it had almost entirely vanished by June and the official ski season start,when the next substantial falls set up the snow-pack. The snow season has been below average so far,continuing the trend apparent in the long-term records. Meanwhile,winter precipitation in the high country hasn’t been too bad,with the Victorian sites around average to above. NSW sites experienced below average Junes,but have improved since. So there has been plenty of rain and sleet mixed with snow.

    “…there must have been some chill around somewhere.” Read the climate statement.

  10. I live about 10km as the crow flies from here
    http://ski.com.au/snowcams/australia/tas/mawson1.html
    at about 1250m altitude. I’m not interested enough to hike to the rope tow from the car park while carrying skis and boots, then climb down again wearing normal footwear. If mining ghost towns have abandoned wire cables and pulleys the same will one day be true for ghost ski areas. Still we should keep our skis and boots handy in case it snows outside in mid summer.

  11. Can the El Nino and the warmth more generally be linked to any earlier Forbush event or some powerful pickup in the solar wind?

    Yes it has been warm hasn’t it? A blissful turnaround from the cooling trend that has been with us at least since 2005. Sadly we cannot expect it to last. And the cooling trend can be expected to resume shortly. After all that very warm 1998 temperature was a pretty short-lived affair.

  12. Sorry Alfred- you are wrong again. According to Nasa Giss 2005 was the hottest year on record and 2007 tied with 1998. Even pseudo-sceptic Patrick Michaels, speaking at thr Heartland Institue Conference, warns deniers of the dangers of using the spurious argument that temperatures have cooled since 1998 – anyone on the blog still confused by this claim should check out this Climate Crock of the Week “1998 revisited” http://www.youtube.com/watch?v=QwnrpwctIh4
    Steve Fielding are you listening? Obviously you weren’t when Michaels gave this talk at the conference you attended!
    The Bom has just announced that September is alreading breaking records for heat – in some places the temperatures are similar to those usually seen at the height of summer.
    The fact that the sunspot activity is very low may produce lower temperatures (as with Maunder Minimum/LIA)but so far that is not occuring.

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