Will Glasgow's net zero fix a climate crisis that hasn't happened?
But the history books show that at 225 stations measuring temperatures before 1931, the increase to 2000-2021 has been less than half that at just 0.6C.
At the COP26 climate summit in Glasgow in November 2021, many world leaders pledged to power their economies with windmills and solar panels by 2030, 2050 or somewhere in between.
Australian Prime Minister Scott Morrison made a commitment for net zero emissions by 2050, largely thanks to future technology changes that it's hoped will allow the phase-out of fossil fuels.
So despite claims that the climate debate is over, the time is nonetheless ripe for a fresh look at historic Australian climate documents that raise questions about exactly what will be achieved if we risk our standard of living by reducing the "pollution" of CO2.
In 1933 the Council for Scientific and Industrial Research, nowadays better known as the CSIRO, published a document titled Meteorological Data for Certain Australian Localities which comprehensively detailed average monthly temperature observations at hundreds of stations based on Weather Bureau records up to 1931.
Among them, 225 have modern day equivalents either in the same location or shifted a few kilometres to the local airport.
Fahrenheit averages in the CSIR document have been meticulously converted to Celsius and compared with unadjusted RAW minima and maxima averages for 2000-2021 sourced to the BoM's Climate Data Online platform, including data current to June 2021.
Among the 225 stations, 49 had a mean temperature increase equal to or greater than 1C from <1931 to 2000-2021, averaging 1.3C, while 176 stations had an increase less than 1C, averaging 0.4C.
All up, the 225 stations - more than twice as many as the 104 stations used for ACORN national temperature estimates - averaged a mean increase of 0.6C.
Tasmania had the biggest increase of 0.9C from <1931 to 2000-2021 and South Australia had the smallest increase at 0.2C.
Windorah in Queensland had the biggest mean temperature increase among all 225 stations, warming by 2.4C, while Bridgetown in WA had the biggest decrease at -1.2C.
The CSIR document also detailed <1931 rainfall at all 225 stations. Changing rainfall patterns have a lot to do with temperature trends, so let's get into some nitty-gritty with a table comparing averaged min, max, mean and average monthly rainfall across Australia and in each state or territory.
Note that based on the 225 stations, Australia's mean temperature increased from 18.01C before 1931 to 18.57C in 2000-2021, a warming of 0.56C, while average monthly rainfall decreased from 57.86mm to 53.85mm.
Let's dig even deeper and compare <1931 monthly temperatures and rainfall with observations at the same locations in 2000-2021.
To simplify the table above, there was a rainfall decrease from <1931 to 2000-2021 in eight months (January, April, May, June, July, August, September, October). In those months, average maxima increased 0.73 and average minima increased 0.45C.
There was a rainfall increase in four months (February, March, November, December). In those months, average maxima increased 0.35C and average minima increased 0.73C.
That's what happens to maxima and minima when rainfall increases or decreases. If two thirds of all months have less rain with associated cloud cover, it's not surprising that mean temperatures rose by an average 0.6C.
Can we blame the shelters?
Critics might by now be jumping and down, pointing out that many of the <1931 temperatures dating back to the mid 1800s were recorded in non-Stevenson screen shelters that warmed maxima and/or minima or produced cooler maxima and/or minima.
True, but 225 weather stations is a lot more than the 104 used by ACORN to calculate national averages and their greater density within the different climates, stretching from far northern Australia to the furthest south, provides a more accurate average.
There were a variety of shelters used in different jurisdictions prior to Stevensons, each with a tendency to warm or cool minima and/or maxima, or sometimes be spot on.
There are far more locations among the 225 CSIR stations not affected by urban heat and industrial/vehicle smog which are ignored in the ACORN homogenisation process that mostly adjusts historic daily observations so they're cooler.
The 225 stations include all the capitals and major regional centres, eight of which are excluded from ACORN's 104, yet still the mean temperature only increased 0.6C from <1931 to 2000-2021.
See Temperature accuracy for further information about screen influence.
These collate average maxima and minima prior to 1950 at 79 weather stations in the same locations today, and a comparison with 2000-2021 averages at their modern day equivalents shows the mean temperature increased 0.41C (18.15C > 18.56C).
Almost all of the 79 stations had Stevenson screens by the first decade of the 1900s so they have 19 years more "accurate" observations than in the CSIR analysis.
Time for a bit more nitty-gritty, with the table below comparing temperatures at the 79 stations sourced from the CSIR <1931 dataset, the Year Books <1950 dataset and the BoM's CDO for 2000-2021.
This comparison of CSIR, Year Book and 2000-2021 temperatures at 79 stations suggests maxima cooled 0.07C from <1931 to <1950 and warmed 0.64C from <1950 to 2000-2021. The data suggest minima warmed 0.12C from <1931 to <1950 and warmed 0.16C from <1950 to 2000-2021.
The Year Books also log extreme temperatures recorded each month at the 79 stations prior to 1950. When averaged among all the hottest days each month before 1950, they were 0.05C warmer than the average of the hottest days observed in each month at the current stations during all their years of operation up to 2021.
The coldest days each month averaged prior to 1950 were 0.30C cooler than the average of coldest days in the records of existing stations up to 2021. This suggests either climate warming or good luck for people who don't like extremely cold weather.
The Year Books also provide data on the most extreme 24 hour rainfall recordings at 74 stations which can be compared with their modern day equivalents, showing they averaged 413.0mm before 1951.
This compares with an average 300.4mm for extreme rainfall days at the current stations up to 2021, with total rainfall on those extreme days at 30,558.6mm before 1951 and 22,232.7mm at the current stations.
The wettest ever day was 907.0mm in 1893 and the wettest day since recordings started at the 74 stations operating in 2021 was 800.9mm at Port Douglas in 1911.
The table below shows decadal blocks of average and total volumes for the 10 most extreme 24 hour rainfall recordings each year in Australia since 1910:
This data shows the average and total volumes of rainfall in the wettest days since 1910 peaked in the 1970s, a decade the BoM acknowledges had the highest rainfall levels ever recorded in Australia.
Extreme rainfall days with flooding downpours can be connected to cyclones, and the rainfall decline since the 1970s is probably related to Australia's reduced frequency of severe and non-severe tropical cyclones since 1970/7, as charted below (source BoM - Tropical cyclone climatology):
Other historic documents
Four other historic climate documents have been analysed (see here), with all their Fahrenheit temperatures converted to Celsius and compared with 2000-2021 at equivalent stations in the same locations.
These suggest mean temperatures increased 0.6C from <1912 to 2000-2021 (19.2C > 19.8C), which is the same as the 0.6C mean temperate increase in the CSIR <1913 dataset.
The 20 regional locations in the Hunt dataset saw a 0.55C mean temperature increase (19.50C > 20.05C) while the seven capital cities saw a 0.95C increase (18.25C > 19.20C).
The Hunt dataset also has rainfall data showing pre-1912 average annual rainfall at all 27 locations was 627.4mm, which compares to 617.6mm in 2000-2021 - a 1.6% reduction.
These suggest mean temperatures increased 0.2C from <1909 to 2000-2021 at the 10 locations (14.0C > 14.2C).
The dataset provides 12 locations that can be compared with modern equivalents and suggests their mean temperatures increased 0.8C from <1863 to 2000-2021 (16.7C > 17.5C).
Five of the 12 locations are capital cities and these had a 1.3C mean temperature increase from <1863 to 2000-2021 (15.8C > 17.1C), while the seven regional locations had a 0.5C mean temperature increase from <1863 to 2000-2021 (17.3C > 17.8C).
The 20 stations had a 0.8C mean temperature increase from <1899 to 2000-2021 (19.7C > 20.5C), which is the same as the 0.8C increase among the 36 WA stations in the CSIR <1931 dataset.
In the Cooke dataset of 20 WA stations, the mean maximum increased 1.0C from <1899 to 2000-2021 (25.2C > 26.2C), while the mean minimum increased 0.5C (14.2C > 14.7C).
Those four different historic dataset increases in mean temperatures compared with 2000-2021 observations (0.6C, 0.2C, 0.8C, 0.8C) average to 0.6C. Throw in the CSIR and Year Book increases in mean temperature (0.6C, 0.2C, 0.8C, 0.8C, 0.6, 0.41C) and the average is 0.57C.
So historic unadjusted temperature records all show a mean temperature increase around 0.6C since before 1950 to 2000-2021, compared to the BoM's estimate of 1.44C from 1910 to 2019, and decimal distribution analysis suggests instrument/observation influences tied to 1972 metrication, the advent of automatic weather stations in the 1990s and a mystery change in 2013.
An understandable conclusion might be drawn that official temperature trend calculations since 1910 are unreliable.
Australia's commitment to 2050 net zero emissions is based on homogenised cooling of historic observations to "correct" these unreliable temperatures through ACORN 2.1.
ACORN ignores urban and/or airport heat in regional centres, an acknowledged artificial warming caused by 1972 metrication and evidence that one second readings at automatic weather stations since the 1990s exaggerate maxima in particular.
In the wake of the Glasgow climate summit and despite questions about historic temperature records being a debate said to have been settled, both original and adjusted historic temperatures provide shaky grounds for Australia's commitment to rebuild its economy, industries and energy infrastructure to eradicate CO2 emissions blamed for a climate crisis that might not have happened.
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