TREND Australia TREND summer TREND temperature TREND

Some people have wondered about the trend in Australia’s summertime daily high temperatures.

The last post discussed Australia’s hottest summer (the latest) and Jennifer Marohasy’s attempt to pervert the truth. But I didn’t talk about the trend, which must have surprised regular readers because I tend to emphasize that. A lot. I did show this graph:


The red line (and pink shading) shows an estimate of the trend, indicating it doesn’t follow a straight line. But I didn’t talk about that, or do any statistical testing, I was busy showing the folly of Jennifer Marohasy’s claims.

I’m told that the question was put, do Australian summertime temperatures show a trend — with statistical significance no less — if we only used the time span that Jennifer Marohasy had to delete to get the result she wanted? That would be everything after the summer of 1997/1998.

This usually leads to questions of “how long a time span do you need for statistical significance?” I don’t want to turn this into one of my math posts (although I do enjoy those), I’ll just say that there’s no fixed time span. It depends on how big the noise is (the part we’re treating as random) and of what type (there’s more than one kind of random noise), and on how big the signal is.

Anyway, I’ll take up the challenge and find whether Australia’s summertime high temperature shows a significant trend, using only the time span Jennifer Marohasy whacked. Here it is:

I’ve plotted a trend line estimated with least squares regression (in red) together with its uncertainty range (pink shading). For those who like statistical tests, this one passes: the “p-value” is 0.004, and if you don’t know what that means don’t worry, it translates to what we’d call “99.6% confidence.” For the statisticians among us, I also tested it using the Theil-Sen slope estimate. Again, the result is statistically significant — but only at 98.5% confidence.

The rate estimated is very large; for least squares regression it’s 0.8 °C per decade. Come to think of it, that’s huge! But — and this is a big one — the uncertainty in that estimate is also very large. Make that rate 0.8 +/- 0.5 °C per decade. Then add extra uncertainty because I don’t like to trust analyses based on fewer than 30 data points.

That’s one of the reasons we don’t usually estimate rates based on such short time spans. We’ll get an answer, but the range of possibilities will be so large that we can’t really pin things down so the answer we do get isn’t useful, because it doesn’t tell us anything we didn’t already know.

In this case it does tell us that the trend is upward at the moment. Even though we already knew that, it’s useful for ridiculing the ridiculous ramblings of Jennifer Marohasy.

We could repeat the exercise using only the data from Rutherglen, Jennifer Marosasy’s choice. In that case, the estimated trend “since she whacked the data” is even bigger than it is for the Australian continent-wide data! But — and this is a big one — it does not pass statistical significance. That’s because the estimated trend uncertainty is also even bigger than for the continent-wide data, enough so to make the estimate rate no longer “statistically significant.”

And that’s because the noise — the random fluctuations from one summer to the next — are a lot larger for a single location (like Rutherglen) than they are for a continent (like Australia).

And that, my friends, is another reason that Jennifer Marohasy (and lots of climate deniers) rarely pass an opportunity to focus on a single location or a small area. The data with the highest noise level will be the data least likely to show the trend. The trend they fear.

Australians should fear those trends. They should also rise up in fury over the tactics of Jennifer Marohasy and her ilk, producing idiot nonsense to be spread far and wide on social media and eventually from the mouths of the likse of Scott Morrison. Marohasy and her comrades are the ones who give idiot politicians their ammunition.


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16 responses to “TREND Australia TREND summer TREND temperature TREND

  1. Interesting analysis.

    Your graphs indicate that you looked at high temperature anomalies. It might also be interesting to look at trends in daily low temperatures (low temperature anomalies?) over this period. In a couple of cases that I have looked at, daily lows increased faster than daily highs (e.g., Minneapolis, June-August, 1978 – 2012). Failure to see normal cooling at night could also contribute to the drying of vegetation, leading to increased fire risk. And if the signal of daily low temperature increases is stronger than the signal of daily highs, you might get statistical significance in cases where you don’t with the analysis of daily high temperatures.

    • I’ve looked at temperature data for Australia. The decadal data seems to indicate up until and including the 1990s, nights were warming faster than days. This century, days appear to be warming faster than nights. (I’m planning to follow up this unexpected finding, but it may be a while before I get around to doing that.)

      See the decadal chart in this article:
      https://blog.hotwhopper.com/2020/01/2019-goes-out-with-many-bangs.html

      Last year, 2019, the increase in the annual (average daily) maximum for all Australia was much greater than the increase in the minimum. (See charts in the same article.)

  2. 0.4 K/decade is still pretty huge. It would mean 3.2 K above 2020 level, which means some 5 K above 1850 level.
    Furthermore, I consider, that a sufficiently high price on GHG emissions has to be installed in every developed and semideveloped country.
    In the EU we currently see the beneficial effect of cap-and-trade in spite of the system having still much to many allowances circulating.

  3. As usual this was very clearly presented. Thanks. One comment I have here is that I’m surprised not to see an effect of La Nina in these results. I kind of imagined Australia to be heated by the pooling of warmed water in the western Pacific and then cooled when that warm water heads east to the Americas. That seems rather misguided. How does ENSO typically affect Australia (and Indonesia, etc)?

  4. Hi guys. I’ve got this person who’s posted this claim:

    https://www.deviantart.com/kajm/art/Oooops-826360863

    He believes that the 1974-5s bushfires were worse than the current trends. Considering that the bushfires are still ongoing and that that one the source he provides is Dr. Roy Spencer, who is a creation scientist. Yeah. But I prefer to have a well-detailed refutation and I’m hoping to find it here.

    Here is a more credible source. Here is another.

    • Looking at the info for the 1974/75 fires, the largest areas burnt were in what you might call the outback. Fires in remote areas of Australia are normally left to burn out except for where there are properties in the path (which would be defended).

      The fires of main concern this year are in more populated parts of the eastern states, in national parks and surrounding areas, including many towns and farms. These fires are managed in an attempt to contain them, saving lives and property, and ultimately control them. Some effort is made to protect priceless wilderness areas in national parks but this can be extremely difficult in rugged country. It’s mainly done through accessing fire tracks (built for purpose), building fire breaks, backburning and, if conditions permit, aerial spraying. (There are also fires in WA, one of which is threatening homes in suburbs of the capital city, Perth; and fires in the Adelaide Hills.)

    • The graph shows over 100 million hectares burnt in 1974/75, and this in a country of total area 770 million hectares. I was alive and living in Australia that summer. I think I’d remember if one seventh of the continent was burned.

      [Response: As has been pointed out, most of the fires in 1974/75 were in uninhabited areas, and weren’t even discovered until later from satellite photos.

      The entire “more area burned before” is another attempt to confuse people into believing this is natural, not man-made. It’s a lie. It’s a pernicious lie.]

    • Lawrence McLean

      That deviant art post is very misleading. The 1974 -5 fires were cause by unusually very heavy spring rain in the desert regions of New South Wales. The resulting grass growth dried and caught fire in the following summer.

      The figures for the current fires are now very much larger than the numbers shown in that post (>10.000,000 hectares) and are in Forest areas, even Rain forests, which have existed Millions of years without fires, are now burning!

      The current fires are due to intensely dry, hot and windy conditions. In the area I live, the winter rains have failed 3 years in a row, which is unprecedented. It is climate change. The liars who deny climate change stubbornly refuse to abandon their religion and direct there anger at “Greenies” who they solely blame for the fires.

      • @Lawrence McLean,

        Just a side comment … The pattern of heavy rains in Spring leading to incredibly high fire conditions later is a pattern seen among many forest and savannah ecosystem types. A markedly different type in Bar Harbor, Maine, experienced this leading to the great fires of 1947.

        I’m not arguing for decoupling from climate disruption at all … Indeed, extreme precipitation is a signature of climate disruption (per Clausius-Clapeyron). It’s just that manifestations aren’t necessarily obvious, and, to the degree the general public doesn’t appreciate these connections, the Malfeasant Misinformers have an easier time distracting them.

    • Well, perhaps the bushfires in 1974/5 *were* worse in terms of area burned, but as your second source mentions, those were in places where hardly anyone lived. At present the bushfires are in places where many people live – which also means there is a major effort ongoing to minimize their spread (both before and after they actually happened). And yet it continues.

      It’s a good example by Roy Spencer of how to mislead with facts, by not taking into account the different context. It reminds me of the “CO2 was much higher in the past” argument, where lower solar output, different location of the continents and even the higher temperature at the time is completely ignored.

    • Nick Stokes discusses it too. It appears to be an anomalous wiki entry – not necessarily incorrect but that there are many other years when similar areas were burnt but not shown in wiki.
      https://moyhu.blogspot.com/2020/01/a-trap-with-bushfire-area-statistics-in.html

  5. I was mostly wrong about Australia. But temperature and drought should respond to ENSO, and I think that effect should be detectable in fire season. Perhaps ENSO influences are swamped by the warming trend…?
    https://www.abc.net.au/news/2017-10-19/what-el-nino-la-nina-mean-australian-weather/9053464

    • The El Nino phase make it warmer and drier in eastern Australia. We didn’t have an El Nino (the Gods help us when we do). But there is also the Indian Ocean Dipole. When it is positive it causes hot and dry conditions across the continent. And this year it was apparently a record positive event. I wonder Tamino if there is a significant trend toward more frequent and/or more severe positivity in the IOD?

  6. The high teperatures may have somethng to do with the drought last year. With little or no evaporationto cool the surface it will warm very fast. With wind and a few careless people and a lot of wood you get this terrible situation of wildfires out of control.

  7. The sudden stratospheric warming event was also significant for the present bush fire season.
    https://theconversation.com/the-air-above-antarctica-is-suddenly-getting-warmer-heres-what-it-means-for-australia-123080

  8. Interesting that Marohasey should choose data from Rutherglen. The farmers there must be seeing something that she doesn’t.
    Among other things it is a wine producing area. It is known for producing rich reds and is Australia’s top fortified wine producing area. One of the World’s top fortified wine producing areas for that matter.
    They and other Australian inland wine producing areas are planting more grapes from hot areas in anticipation of further warming. I’m sure they might have a few words to describe her.

    [Response: Temperature change can definitely influence wine growers]