by Anthony Cox
It’s official, using BoM data the Australia Institute (AI), a left-leaning think tank which is just another alarmist ginger group, has declared that compared to 1950-1969, Summers are getting longer. In its press release is this dire graph:
Looks bad, doesn’t it? Fortunately, it’s just the usual cherry-picking of already adjusted BoM data.
What the AI has done is compared an El Niño dominated period, a positive Pacific Decadal Oscillation (PDO) with a negative PDO, dominated by La Niña. El Niño, which gives the world warmer and drier conditions, and La Niña, which gives cooler and wetter conditions, clump together into 30+ year periods. There was a positive PDO at the beginning and end of the 20thC continuing into the 21stC, with a negative PDO in the middle. So, the last 120 years or so have been dominated by El Niño conditions which in itself is sufficient to explain the temperature increase:
As shown the PDO phase changes from El Niño to La Niña along with the Atlantic Multidecadal Oscillation explains the 20thC temperatures.
In addition, the temperature increase during the first El Niño period at the beginning of the 20thC is almost identical to the temperature increase during the second El Niño period at the end of the 20thC as Judith Curry explains:
But the La Niña period from 1940-1976 featured cooler and wetter conditions. During this wet and cooler period, seasons were much more demarcated. During the El Niño periods, spillage of warmer temperatures into Spring and Autumn occurs. The AI’s comparison is simply based on a false premise between 2 different, naturally occurring climate patterns.
But despite this cherry-picking by the AI, their own figures are incorrect. The AI report says this:
The beginning of each season is defined by reference to the historical daily average temperature on the first day of the season. Seasons are defined as per the traditional seasonal calendar:
• summer starts 1 December,
• autumn starts 1 March,
• winter starts 1 June, and
• spring starts 1 September.
For each weather station, the average temperature on each of these dates in 1950-1969 is the temperature that marks the beginning of the season. The dates on which these benchmark temperatures were reached over the last twenty years are the dates on which the seasons are said to now begin.
The report then gives examples. Page 35 of the study states that the starting temperature for Autumn in Hobart is 16.5C and Autumn in 1999-2018 starts on 18 March whereas it used to start on 1 March in 1950-1969. Chris Gillham has done a quick analysis of the IA’s conclusions which are based on the already adjusted BoM temperatures:
I know this isn’t their technique but I thought I’d average all the 18 March in 1950-1969 and 1999-2018, and compare their mean temperatures ...
RAW 1950-1969 : 16.85C
RAW 1999-2018 : 16.70C
ACORN 2 1950-1969 : 17.10C
ACORN 2 1999-2018 : 16.80C
Okay, so 18 March is now their official start to autumn despite the fact that on that particular date - since they want to be fussy - the day is cooler over 1999-2018 than 1950-1969 in both adjusted and unadjusted. The mean temp of March 18 is pretty close to their starting temperature, but not quite.
In both the raw and heavily adjusted ACORN 2 figures the base period of 1950-1969 is warmer than the modern period! Chris admits he didn’t use the AI’s methodology, instead using a much more reasonable and accessible averaging technique.
Like their adjusted data the alarmists’ technique is suspect and designed for one thing: to support the narrative that it’s getting hotter.