Climate change

November 18, 2009

Two years, three record heat waves in southeastern Australia

nov09tempSummer 2009 — 2010 hasn’t even begun in Australia, and yet we are already sweltering under another record heat wave — the third in two years. Temperature records for the month of November have been broken across the region, caused by a blocking high pressure system over the Tasman Sea. This follows an abnormally hot winter, including Australia’s hottest August on record.

In my home city of Adelaide, we’re still experiencing the first official November heat wave since records began (a ‘heat wave’ being defined here as five or more consecutive days above 35°C). Last Saturday 7th Nov, the mercury climbed to 34.4°C, and on Sunday the heat wave officially commenced. From Sun 8/11 to Sat 14/11, the maximum temperatures have been 36.7°C, 37.0°C, 38.6°C, 39.2°C, 39.0°C, 38.7°C  and 39.5°C. The forecast for Sun 15/11 is 40 °C, after which the temperatures will drop back to the high 20s for a few days, and then another burst of days in the low-40s. If Sunday’s scorcher is realised (confirmed: 39.4°C), the heat wave will have lasted for 8 days [confirmed] (almost 9, with Sat 7/11 also almost reaching the threshold 35°C). Not a great time to hold a Christmas pageant — poor Santa!

Time for some context. The closest Adelaide has ever come to a spring heat wave was 4 days in a row 1894. This month’s event will double that — a doubling like this is not twice as unlikely, it’s orders of magnitude more unlikely. Consider that in prior to 2008, the record length for an Adelaide heat wave in any month was 8 days (all occurring in summer). Now, in the space of less than 2 years, we’ve had a 15 day event in Mar 2008 (a 1 in 3000 year event), a 9 day sequence in Jan/Feb 2009 (which included 8 days above 40°C and 13 consecutive days above 33°C), and now, another 8 day event in Nov 2009. How unusual is this? There have been 6 previous heat waves that lasted 8 days, many more of 7 days, more still of 6, and so on — the return time is logarithmically related to it’s length. Given these data, and the fact that the latest spring event has equaled previous all-time summer records (!), and the alarm bells should rightly be ringing. Statistically speaking, it’s astronomically unlikely that such a sequence of rare heat waves would occur by chance, if the climate wasn’t warming. But of course, it is.

The November 2009 heat wave has not been restricted to Adelaide — it’s affecting most of southeastern Australia. Here’s a useful report from NSW (ABC Sydney) by Graham Creed, which noted:

Adelaide’s run of record November heat has been in the media spotlight for much of the week but there have been longer runs of heat. Batchelor, a mining town 100km south of Darwin with a permanent population under 400, has just recorded its 80th consecutive day of temperatures at or above 34.7 degrees.

A regularly updated summary of the current heat wave and the records that it’s breaking, can be found on Wikipedia.

Regarding potential links to climate change, BNC commenter ‘perps’ notes:

In this clip from the “7.30 report” both John Nairn from the Bureau of Meteorolgy and Euan Ferguson from SA Country Fire Authority attribute tthe conditions to climate change as indicated by the IPCC who now say that a trend is emerging. John Nairns also explains why we are seeing these extreme heatwaves – high pressures keep re-establishing over SE Austalia without the intervening lows which used to bring cooler southerly winds.

Further along this line, ABC News radio’s The World Today program ran a story on the Nov 2009 heat wave yesterday: Adelaideans cower under scorching heatwave. Here are a few quotes from me:

NANCE HAXTON: The extreme weather pattern has left many wondering what’s caused the heatwave.

The weather bureau puts it down to a stationary high pressure system over the Tasman Sea, which has prevented cooler air moving up from the Southern Ocean to South Australia and Victoria.

But other experts see another pattern at work. Professor Barry Brook from the University of Adelaide’s Environment Institute says the increasing occurrence of heatwaves in recent years is pointing to climate change.

BARRY BROOK: Heatwaves are going to become more frequent and I think that’s what we’re seeing. That the sort of heatwaves that may have occurred once every few summers in Adelaide in the past, may be a yearly event now and occasionally we’re going to get heatwaves that far exceed anything we’ve had in the past, such as what we had in January this year and in March last year.

NANCE HAXTON: And so that would have policy implications as well?

BARRY BROOK: Well in the immediate term heatwaves are bad for public health, especially those people who are vulnerable to heat stress and haven’t got the ability to cope with that by turning on the air conditioner or going in a pool or whatever.

And that’s what happened in the major heatwave that we had in January, that a lot of elderly people especially died in their homes as a result of heat stroke. So that puts a stress on emergency services and of course it’s bad for the community.

In the broader context hot temperatures early in the year or late in the year put a lot of stress on the plants and animals that live around this area too. It increases their water stress and of course it changes their physiological ability to tolerate heat.

And so all of that put together means more young animals tend to die, more trees die off that are vulnerable and ultimately you get a shift from one type of flora and fauna in a region to another.

And it’s going to get hotter and more hot days, more heatwaves, drier conditions and Adelaide is going to end up looking more desert-like than it currently does today.

Of course they had to end with some quotes from a ’sceptic’; this time it was William Kininmonth with the usual “natural cycle”, “random things” happen, etc. line.

Another regular commenter, John Newlands, points out an interesting implication for energy supply –

Later on I would like to know the capacity factor this week for South Australia’s 800 MW of nameplate windpower. I’ve pointed out before that SA’s power demand of 2.8 GW in March 2007 gives us (Aust pop 22m)/(SA pop 1.1m) = 20 so that a ‘national’ heatwave would give Australia a peak demand of 56 GW…

… Wishes can come true, the AEMO website already had capacity info for 10/11/09

The demand in the South Australian region peaked at 2947 MW at 16:30hrs, due to temperatures reaching a high of 38.6ºC in Adelaide. Wind generation in the afternoon was less than 70 MW. Demand in Victoria reached 9386 MW and temperatures reached 35.2ºC in Melbourne.

70 MW actual/ 800 installed for SA is an instantaneous c.f. of about 9%. Conclusion: wind doesn’t help in heat waves.

Finally, I see that my old haunt of Darwin also cracked the record books – October 2009 was that northern tropical city’s hottest month on record, with an average maximum temperature of 34.8°C. This beat the previous all-time record (Oct 2008) by 0.4°C and followed hot on the heels of its hottest August on record. Makes me glad I left Darwin in February 2007! (at least Adelaide’s heat waves finally break).

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