Extreme Weather Events 3: Sydney

Are extreme weather events showing up in Australia’s largest city?

Floods and bushfires might affect smaller areas, but droughts, heatwaves, and very heavy rainfall from large weather systems affect large areas. All of the above have occurred near Sydney in the past few years: surely there should be visible signs in temperature and rainfall.
First, rainfall.

In July and October 2022 flooding affected the western Sydney region again, with The Conversation of course saying “climate change is projected to bring far worse extreme rain events than in the past.”

For long term rainfall I look at Sydney’s longest rain records, at Observatory Hill and the Botanic Gardens. Figure 1 shows their location.

Figure 1: Central Sydney, courtesy of Google Maps

Observatory Hill rain records start in July 1858, but the original data ends in August 2020. I choose not to splice data from old and new gauges. Botanic Gardens start in 1885 but there is a large gap, with continuous data from late 1909 to the present. Figures 2 and 3 plot daily rainfall for each:

Figure 2: Observatory Hill daily rain

Figure 3: Botanic Gardens daily rain (1910 to 2022)

Long term means:

Figure 4: 10 year running means of rainfall at Observatory Hill and Botanic Gardens

Note that the means are similar until about 2010 when they start to diverge. Reasons might include changes to the sites. Rainfall was clearly higher in several previous decades.

Figure 5: 10 year running Standard Deviations

There was much greater variability in Sydney’s rainfall for most of the 50 years from 1950 to 2000. To show Standard Deviation relative to mean rainfall:

Figure 6: 10 year running Standard Deviations divided by 10 year means

Which shows there is little daily variability in rainfall in recent years, and both sites are comparable.

I will now analyse Botanic Gardens data in more detail.

Figure 7: Running 365 day means

2022 was the wettest year on record, followed by 1950.

Rainfall accumulated over several days is a factor in large scale riverine flooding such as occurred in Sydney’s west.

Figure 8: Four day total rainfall

Clearly there were many much greater 4 day rain events in the past than in the latest floods.

I measure “droughts” by counting the number of days with less than 4mm of rain in running 365 day periods.

Figure 9: Running 365 day counts of days with under 4mm of rain

2022 was by far the most consistently wet. There is no sign of increased drought in Sydney.

Conversely, do recent years have more days with high rainfall?

Figure 10: Running 365 day counts of days with over 100mm of rain

No. Only 3 days in 2022, while 1999 had 5, and many others in previous years had more than 2022. It seems that the Sydney region, going by the Botanic Gardens rain gauge, has less extreme rainfall than the past.

I now analyse temperature at Sydney Observatory Hill, using the latest version of Acorn to 2021, and Climate Data Online for 2022 and January 2023 up to Australia Day.

Figure 11: Daily Maxima Sydney Observatory Hill 1910 to 26/1/2023

Maximum temperatures in Sydney, according to the best the Bureau can provide, have warmed at 0.9 degrees Celsius per 100 years. Decadal means show an almost identical trend.

Figure 12: 10 year mean Tmax

Standard Deviation measures daily variability, and 10 year mean Standard Deviations show some interesting patterns:

Figure 13: 10 year running Standard Deviation, Sydney Tmax

Variability is greater with higher temperatures and less with lower temperatures, and temperatures should be related to rainfall- because a dry period will have hotter days and usually cooler nights. Temperature adjustments might interfere with this.

Whatever, there were several past periods with higher Standard Deviations than the past decade, and when divided by the 10 year means the contrast is even greater:

Figure 14: 10 year running Standard Deviations divided by 10 year means

Are days getting hotter? Well, years are, mostly:

Figure 15: 365 day running means of Tmax

Highest and lowest daily maxima in 365 day periods are not co-operating:

Figure 16: Highest Tmax in 365 day periods

The hottest day was back in 1939, and 2022 had the lowest “hottest day” in a 365 day period on record, with the hottest day being 31.9 degrees.

Figure 17: Lowest Tmax in 365 day periods

Several past winters had cooler maxima.

But is Sydney getting more frequent hot and very hot days?

Figure 18: Running 10 year counts of days over 34.9 degrees

Figure 19: Running 10 year counts of days over 39.9 degrees

The last 10 years have had fewer hot and very hot days than in the past.

What about heat waves, when there are strings of hot days? The definition appears to have changed, but if we consider three hot days in a row to be a heat wave:

Figure 20: Running 10 year counts of 3 consecutive days over 34.9 degrees

There is a very small trend (0.8 in 100 years) but there were many more 3 day heatwaves in the past.

Figure 21: Running 10 year counts of 3 consecutive days over 39.9 degrees

There is a decreasing trend of very hot heat waves (more than 3 less per 100 years), with nearly three times as many 3 day heatwaves of 40 degrees or more in the 10 years to 1982 as in the past 10 years.

Conclusion:

Contrary to popular belief encouraged by politicians and the media, in Australia’s largest city it is clear that:

Rainfall and temperature variability is LOWER than in the past

Droughts are NOT increasing

Extreme rainfall is NOT increasing

Dry years are NOT increasing

Very hot days are DECREASING in frequency

Heatwaves are NOT increasing and are very much LESS COMMON than 40 years ago.

If anything, Sydney’s weather is becoming less extreme and more benign. That should be good news.

We are still waiting for the “projections” of more extreme weather to arrive.

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Extreme Weather Events: 2

Further to my post yesterday about the Climate Council’s recent fear mongering, with my look at whether the recent flooding at Fitzroy Crossing could be due to increasingly severe rain events, here are two more locations.

I calculate the 10 year running standard deviation of daily rainfall, the 10 year mean, and because the standard deviation must change as the mean changes, I divide the 10 year standard deviation by the 10 year mean.

Early this year there was sever flooding in northern New South Wales. Brays Creek is near Mt Warning about 40 km north of Lismore. Here is the standard deviation divided by average rainfall:

Rainfall over the past 10 years is less extreme than it was 40 to 50 years ago.

The Bruce Highway to north Queensland was blocked for several days, as it normally is every Wet season, by flooding at Goorganga Plains just south of Proserpine. Is rainfall becoming more extreme? Here is the raingauge at Lethebrook, using the same technique.

Nothing exciting to see there either.

Extreme Weather Events: 1

Last night On Wednesday night 18 January, the Climate Council released their latest doomsday publication, with the support of Beyond Blue (they’re now off my list of charities to donate to.)

“HIDDEN MENTAL HEALTH TOLL OF WORSENING CLIMATE DISASTERS ON AUSTRALIANS REVEALED WITH NEW NATIONAL POLL”

Climate Councillor, climate scientist at the Australian National University and author of Humanity’s Moment: a Climate Scientist’s Case for Hope, Dr Joelle Gergis said: “The results of this poll are confronting. It’s heartbreaking to realise that many Australians are living with significant levels of distress related to the reality of our changing climate. It shines a light on this invisible mental health crisis that is undermining the stability of our local communities all over the country.

“We need to have a national conversation about climate change adaptation and listen to the experiences of people who have lived through these disasters.

“Extreme weather events are going to escalate as our planet continues to warm, so the impacts we have witnessed in recent years are really just the tip of the iceberg. We urgently need to develop plans that protect and support our local communities as climate change-fuelled disasters continue to upend the lives of countless Australians.”

Time for a reality check:

Is there evidence of increasing climate extremes?  Rainfall and temperature are easily measured and data is freely available from the BOM.

First example:  The recent flooding at Fitzroy Crossing. 

A useful measure of extremes is Standard Deviation.  For this technique I am indebted to Willis Eschenbach whose recent post at WattsUpWithThat sparked my interest.

I calculate the 10 year running standard deviation of daily rainfall, the 10 year mean, and because the standard deviation must change as the mean changes, I divide the 10 year standard deviation by the 10 year mean.

The nearest rain gauge with a reasonably long record is Fossil Downs.  Here is the 10 year average daily rainfall:

As you can see average daily rainfall (which nearly all falls in the Wet) has nearly doubled since the decades to the 1960s.

10 year standard deviation:

No wonder people are anxious!  The 10 year figure is very high (but not as high as the 1980s!  Was it more extreme 40 to 50 years ago?)

But here is the standard deviation divided by average rainfall:

This shows that relative to the average, rainfall extremes are actually getting smaller.

Over the next few days I will show rainfall and temperature plots for several Australian cities.  Stay tuned.

Australian Temperature- Satellites or Surface Stations?

For years we have been very sceptical about the official Bureau of Meteorology (BOM) temperature record which is based on 104 surface stations in the ACORN-SAT (Acorn) network.  In this post I look at one of the main reasons for doubting the veracity of the surface record- the increasing divergence from the satellite record.

First up I should say that the two records should not necessarily agree, because they measure two completely different things.  Surface stations measure the temperature of the air 1.2 metres above the ground and report the highest and lowest one second samples each day at 104 locations.  These are combined in a grid average to give monthly, seasonal, and annual temperatures.  Satellites measure temperatures of the atmosphere from the ground to many kilometres up, every second, over a wide area for each pass.  These are similarly combined by algorithms to calculate a monthly average for (in this case) the land area of Australia’s Temperature of the Lower Troposphere (TLT). 

They are both useful for different purposes but are not easily compared.  Because minimum surface temperatures poorly match TLT, mean surface temperature is also a poor match.  Maxima are a better match, but still not perfect.

For this post I use data from the University of Alabama (Huntsville) (UAH) which calculates anomalies from 1991 to 2020 means.  I have converted Acorn data from anomalies from 1961-1990 means, to anomalies from 1991-2020 means, to match.

Figure 1 shows monthly Acorn maxima data and UAH means from December 1978.

Figure 1: Monthly Surface Tmax and UAH data

Although surface maxima have a much larger range than TLT anomalies, they plainly follow similar trajectories.  12 month running means smooth the data and allow easier visual comparison.

Figure 2: Running 12 Month Means: Surface Tmax and UAH data

Similar, but different at several times.   Annual means show that in some years Tmax and TLT are close to identical, while in other years they have large differences.

Figure 3: Annual Means: Surface Tmax and UAH data

In 2015 I showed the reason for these differences (but not the difference in trends).  The differences between the two datasets are very largely due to variations in rainfall.  In wet years surface maxima are relatively much cooler than TLT; in dry years surface maxima are much warmer.  In Figure 4 I have calculated rainfall anomalies scaled down by a factor of 20 and inverted, to compare with the difference between Tmax and TLT.

Figure 4: Running 12 month Means: Surface Tmax minus UAH and Inverted Rainfall

The match is close.  Figure 5 shows annual values, and trend lines.

Figure 5: Annual Means: Surface Tmax minus UAH and Inverted Rainfall

While annual rain has been slightly increasing (it’s inverted, remember) the relative difference between surface temperature and atmospheric temperature has been increasing at a rate of one degree per hundred years.  That’s odd.  Figure 6 shows the relationship between the temperature difference and rainfall.

Figure 6: Annual Surface Tmax minus UAH versus Scaled Rainfall

For every extra 20mm of rainfall, the difference between surface maxima and TLT decreases by 0.85 degrees Celsius.  The trend lines in Figure 5 should be close to parallel, not diverging.

As well, as rainfall increases, Tmax should decrease, as Figure 7 shows.

Figure 7: Surface Tmax as a Product of Rain

But as we saw in Figure 3, Tmax is increasing faster than UAH.

Furthermore, as surface Tmax increases, TLT should be increasing as well, which it is, but at a slower rate.

Figure 8:  Atmospheric Temperature as a Product of Surface Tmax

Is the atmospheric temperature lagging behind surface temperature?  Figure 9 shows the last two years of monthly values.

Figure 9:  Monthly Atmospheric Temperature and Surface Tmax, January 2020-March 2022

The values are mostly synchronous, with sometimes a delay in one or the other of one month.  (Remember, we are comparing data from 104 stations scattered across the continent, with that of the atmosphere with constantly changing and circulating winds).  When the land warms, the atmosphere warms with it; when the land cools, so does the atmosphere.

Conclusion:

Tmax should not be increasing faster than atmospheric temperature.  There is no real delay in any temperature change, as the atmosphere is heated each day by the land.  Therefore it appears that there must be some fault with the maximum temperatures reported by ACORN-SAT, which appears to be warming too rapidly.

Explanation of the mechanism for rainfall moderation of surface-atmospheric temperature differences:

In wet years more moisture carried upwards condenses, releasing heat, thus warming the atmosphere, while the surface is cooled by cloud cover, evaporation, and transpiration.  In dry years much less moisture is convected, so less heat is released in the atmosphere, while the surface is hotter because of less cloud cover and less evaporation and transpiration.  Thus dry years have a greater relative difference between Tmax and TLT than wet years.

The only energy source is solar radiation heating the land surface in daylight hours, which in turn heats the atmosphere by conduction and convection.  At night as radiation to space rapidly cools the earth, convection also rapidly decreases, so maxima, not minima, are responsible for the relationship with TLT. 

A complication is that in summer (and more so in very wet La Nina years) large volumes of very moist air from the tropical seas to the north converge over northern Australia and penetrate even into southern Australia.  This warm moist air cannot heat the surface but through condensation transfers heat to the upper atmosphere- therefore the difference between surface and atmosphere is even smaller.

More Problems With Australia’s Temperature Record: Part 3

We have seen in Parts 1 and 2 that every extra year of annual data can decrease the temperature trend at a weather station by from -0.02 to -0.03℃ per decade, and that less than half (47% actually) of Australia’s weather stations used for climate analysis have data from 1910, and three of them have insufficient data to calculate trends.

Figure 1 shows a map of non-urban Acorn stations with enough data to calculate trends, at 1910.  The others I have blanked out.

Figure 1: Acorn stations with data for 1910

The network is very sparse.  To estimate a national temperature for 1910 enormous weighting must be given to the values of a few remote stations like Alice Springs, Boulia and Kalgoorlie, so we hope they got the adjustments right!  Unfortunately, in 2015 I found adjustments at Kalgoorlie and Alice Springs were very problemmatic.

The Bureau explains the process of calculating average temperatures here.

Figure 2 shows the BOM map of trends from 1910 to 2020:

Figure 2:  Australian Tmean trends 1910-2020

Note that there a few “bullseyes” which surround stations whose temperature trends are out of phase with areas around them- e.g. Boulia is warmer, Marble Bar is cooler. 

Now here is a paradox.  As the years go by and more stations have data available, the area weighting for each station will decrease, however trends at the newer stations will show increased warming compared with the older ones.  However they will also have more variability.  This will result in oddities as I shall show, and reveals something of the difficulties with the BOM methods.

 Figure 2 is a plot of mean temperature from 1970 to 2020.

Figure 2:  Australian Tmean 1970-2020

The Acorn 2 trend is now +0.23℃ per decade or +2.3℃ per 100 years- a full degree more than the trend from 1910.

Now let’s look at the trend map for 1970 to2020:

Figure 3:  Australian Tmean trends 1970-2020

Note the little “bullseye” around Victoria River Downs, the little “balloon” around Halls Creek to the south-west of VRD, and the little surge to the south-southwest of VRD of 0.05 to 0.1℃ per decade.  Note also that north-eastern Arnhem Land, with no stations, has a warmer pocket.  Figure 4 is the BOM data for VRD.

Figure 4: Annual mean temperature at Victoria River Downs

VRD opened in 1965 and has too much data missing for BOM to calculate a trend.  The area weighting algorithm still gives it a cooling trend of between minus 0.05 and 0℃ per decade (Figure 3).  Que?

With more than 27% of data missing I wouldn’t calculate a trend either, but with only six of 43 years missing I can calculate a trend from 1978:

Figure 5: Annual mean temperature at Victoria River Downs

The trend is -0.09℃ per decade, which is a bit more cooling than the trend map (Figure 3) shows.  Now let’s look at trends from 1980 to 2020.

Figure 6:  Australian Tmean trends 1980-2020

There are more bullseyes, and I have shown temperature trends for some- Carnarvon, Meekatharra, Forrest, Thargomindah, and Gayndah.  But remember Figure 3’s little surge to the SSW?   It now has its own bullseye, and that is Rabbit Flat.

Figure 7: Annual mean temperature at Rabbit Flat

Rabbit Flat opened in 1970 and has a trend of +0.08℃ per decade, which agrees with the trend map in Figure 3.  Now from 1980:

Figure 8: Annual mean temperature at Rabbit Flat

What a difference a few years make in a short timeseries.  The trend of -0.06℃ per decade also agrees with the 1980-2020 trend map.

However, just 328km away Halls Creek shows a warming trend of +0.17C per decade from 1980 – 2020:

Figure 9: Annual mean temperature at Halls Creek 1980-2020

But from 1970 to 2020 Halls Ck is warmer still at +0.19C per decade:

Figure 10: Annual mean temperature at Halls Creek 1970-2020

And at Tennant Creek 441km away the 1970-2020 trend is +0.19C per decade:

Figure 11: Annual mean temperature at Tennant Creek 1970-2020

From 1980 it is +0.06C per decade.

Figure 12: Annual mean temperature at Tennant Creek 1980-2020

Temperatures are trending in different directions and wildly different rates at the closest stations: they can’t all be right!

The method of drawing trend maps is to use anomalies of temperatures of all years of all stations whether or not an individual trend can be calculated, then calculate a gridded average, and from that calculate trends, then spread those trends hundreds of kilometres in every direction- even across the Gulf of Carpentaria from Horn Island to Arnhem Land, as seen in Figures 3 and 6- averaged with the trends propagated by other stations.  If a site has data missing, the grid is infilled with the weighted data from other sites.  

In recent decades this causes great variability because of the short records, which leads to grave doubts about the reliability of some records.  Further back in time, there is less variability because there are more stations, and the longer records smooth and decrease the trends- however the weighting has to be much greater because of the large areas with no data at all for many years. 

The problem is: we can have either a long record, or an accurate record, but not both.

This leads to the obvious conclusion:

The official temperature record since 1910 is just a guesstimate.

More Problems With Australia’s Temperature Record: Part 2

My colleague Chris Gillham at WAClimate uses 58 long term weather stations for his analyses.

And with good reason.  Here’s why.

Figure 1 is a screenshot of the annual mean temperature record at a typical Acorn station, Longreach (Qld) with the linear trend shown.

Figure 1: Annual mean temperature at Longreach

The linear trend is +0.12℃ per decade.  Nine (9) of the 111 years of data from 1910 to 2020 are missing, leaving 102 years.

Australia’s official climate record is based on 112 sites like Longreach.  Of those, 8 are not used for seasonal and annual analyses because they are affected by Urban Heat Island (UHI) effect.  Five (5) of the non-urban stations have more than 20% of their data missing, so the BOM does not calculate trends for them. Of those remaining, only 50 started in 1910, and another 8 before 1915.  What is the effect of different length records on our understanding of how temperatures have changed over the years?

Figure 2 is a plot of the trends of mean temperatures per decade as a factor of the number of years of annual temperature data on record at those 107 Acorn stations with enough data to calculate trends.

Figure 2:  Trend as a factor of amount of data

Stations with  longer data records have lower trends.  The trends at stations with shorter records vary wildly, with some obvious outliers. 

At those stations with UHI effect, the relationship is even stronger.

Figure 3:  Trend as a factor of amount of data at sites with UHI

These sites are in larger towns and cities, possibly with better maintenance and observation practices (although not necessarily better siting).

The slope of the trendlines in the above two figures show that for every additional year of data, temperature trend decreases by about -0.02 to -0.03℃ per decade. In 100 years that could make a difference of as much as three degrees Celsius 0.3C at a well maintained site.

Figure 4 is a map of trends across Australia from 1910 to 2020.  I have shown the years of available data at each site (locations only approximate) and I have circled in blue those 5 sites that have insufficient data.

 Figure 4:  Years of data contributing to 1910 to 2020 trend map

Trends in different regions vary from less than 0.1C per decade to up to 0.3C per decade.  As you can see there is a large variation in the amount of available data in each different coloured band.  That’s for 1910 to 2020.  Note that there are only three (3) non-urban stations with no missing years- Carnarvon, Esperance, and Mt Gambier- which I have circled in red.  There are some big gaps.

In Part 3 I will look at some individual stations and how trends vary in the 51 years from 1970 to 2020.

More Problems With Australia’s Temperature Record: Part 1

Since 2010 I have been documenting problems with different versions of Australia’s official temperature record as produced by the Bureau of Meteorology (BOM).  Since the High Quality (HQ) dataset was quietly withdrawn in 2012 we have seen regularly updated versions of the Australian Climate Observation Reference Network- Surface Air Temperature (ACORN-SAT or Acorn).  We are now up to Version 2.2.  In this Part I shall show the effect of these changes on temperature trends.  In Part 2 I will show how record length affects trends, and in Part 3 I will look at the record since 1970 at some individual stations.

Figure 1 is from the BOM Climate Change Time Series page.

Figure 1:  Australian Official Temperature Record 1910 to 2021

The linear trend is shown as +0.13℃ per decade, or 1.3C per 100 years.  My colleague Chris Gillham of WAClimate has provided me with archived Acorn 1 annual mean temperature data to 2013 which allows this comparison:

Figure 2:  TMean: Acorn 1 and Acorn 2

The result of introducing Acorn 2 has been a much steeper trend:  Acorn 1 trend to 2013 was 0.9℃ per decade.  The trend has now become 0.13℃ per decade. (The extra 9 years have added an extra 0.017C per decade to the trend.)

Figure 3 shows when and how large the changes were:

Figure 3:  Difference between Acorn 1 and Acorn 2

Acorn2 is cooler than Acorn 1 before 1971 and warmer in all but three years since.  Since these were based on the same raw temperatures (with some small additions of digitised data and a couple of changes to stations) the changes were brought about entirely by adjustments to the data.

I calculated running trends from every year to 2013 for both datasets.  As trends shorter than 30 years become less reliable I truncated the running trends at 1984.  Figure 4 compares thre trends to 2013 of Acorn 1 and Acorn 2.

Figure 4:  Acorn 1 and Acorn 2 running trends per decade to 2013

The weather fluctuations of the mid-1970s to 1980s played havoc with trends.

Figure 5 shows the difference between the trends.

Figure 5:  Difference between Acorn 1 and Acorn 2 Trends

The difference ranges from +0.024C per decade for 1910 to 2013, to +0.039C for 1950 to 2013.  Having increased warming by from 0.25C to 0.4C per 100 years (just by making different adjustments) Acorn 2’s trend is much more alarming than Acorn 1’s.

Conclusion:

This is from the BOM’s explanation for Acorn:  

“A panel of world-leading experts convened in Melbourne in 2011 to review the methods used in developing the dataset. It ranked the Bureau’s procedures and data analysis as amongst the best in the world. ‘The Panel is convinced that, as the world’s first national-scale homogenised dataset of daily temperatures, the ACORNSAT dataset will be of great national and international value. We encourage the Bureau to consider the dataset an important long-term national asset.’” ACORN-SAT International Peer Review Panel Report, 2011.

 Acorn 1.0 was apparently such an important long-term asset that it was quickly superseded by Acorn 2 with a much more alarming trend.

Diurnal Temperature Range and the Australian Temperature Record: More Evidence

In an earlier post, I demonstrated through analysing Diurnal Temperature Range (DTR) that the Bureau of Meteorology is either incompetent or has knowingly allowed inaccurate data to garble the record.

A couple of readers suggested avenues for deeper analysis. 

Siliggy asked, “Is the exaggerated difference now caused by the deletion of old hot maximums and or whole old long warmer records?”

Graeme No. 3 asked, “Is there any way of extracting seasonal figures from this composition?”

This post seeks to answer both, and the short answer is “Yes”.

Using BOM Time Series data (from the thoroughly adjusted Acorn dataset) I have looked at data for Spring, Summer, Autumn, and Winter (although those seasons lose their meaning the further north you go).

DTR is very much governed by rainfall differences as shown by this plot.

Figure 1:  Winter DTR anomalies plotted against rainfall anomalies- all years 1910-2020

This shows that in winter DTR decreases with increasing rainfall.  The R squared value of 0.79 means that for the whole period, rainfall explained DTR 79% of the time on average.  However, the average conceals the long term changes in the relationship.

To show this, I simply calculated running 10 year correlations between DTR and Rainfall anomalies for each season, and squared these to show the “R squared” value.  This is a good rule of thumb indicator for how well DTR matches rainfall over 10 year periods.  A value of 0.5 indicates only half of the DTR for that decade can be explained by rainfall alone.  As you will see in the following figures, there are plenty of 10 year periods when the relationship was 0.9 or better, meaning it is ideally possible for 90% of DTR variation to be explained by rainfall.  Here are the results.

Figure 2:  Spring Running R-squared values: DTR vs Rain

There was a good relationship before 1930.  In the decades from then to the mid-1970s it was much worse, and very poor in the decade to 1946. It was poor again in the decade to 2001, and the 10 years to 2020 shows another smaller dip, showing something not quite right with 2020.

Figure 3: Summer Running R-squared values: DTR vs Rain

Summer values were very poor before the 1960s, especially the decades to 1944 and 1961, and dipped again in the 1990s.

Figure 4:  Autumn Running R-squared values: DTR vs Rain

The DTR/Rain relationship was very poor in the decades to 1928, and again before 2001.  The recent decade has also been poor- less than half of DTR to 2020 can be explained by rainfall.

Figure 5:  Winter Running R-squared values: DTR vs Rain

The DTR/rainfall relationship was fairly good, apart from two short episodes, until the 1990s.

I now turn to the northern half of the continent.

A large area of Northern Australia is dominated by just two seasons, wet and dry.  Here is the plot of northern DTR vs Rain for the wet season (October to April).

Figure 6:  Northern Australia Wet Season Running R-squared values: DTR vs Rain

Apart from the 1950s, the late 1970s-early 1980s, and 1998 to 2020, the DTR : Rainfall relationship is very poor, with a long period in the 1930s and 1940s in which rainfall explains less than half of DTR variation (only 13% in the decade to 1943). 

Because the northern half of Australia accounts for the bulk of Australian rainfall, and the wet season is from October to April, this perhaps explains the problems in spring, summer, and autumn for the whole country.

We can get some clues as to the reasons by comparing long term average maximum temperatures with inverted rain (as wet years are cool and dry years are warm).

Figure 7:  Northern Australia Wet Season Decadal Maxima and Rain

The divergence before 1972 and after 2001 is obvious.

The above plots show how poorly DTR (and therefore temperature, from which it is derived) has matched rainfall over the past 111 years.  Low correlations indicate something other than rainfall was influencing temperatures.

In reply to Siliggy, who asked “Is the exaggerated difference now caused by the deletion of old hot maximums and or whole old long warmer records?” the answer appears to be: both, however Figure 7 shows old temperatures (before 1972) appear incorrect, but recent temperatures are at fault too.

The mismatch shows that the Acorn temperature record is not to be trusted as an indicator of past temperatures- and even recent ones.

More Evidence That The Australian Temperature Record Is Complete Garbage

The Bureau of Meteorology is either incompetent or has knowingly allowed inaccurate data to garble the record.

My colleague Chris Gillham at http://www.waclimate.net/ has alerted me to growing problems with the BOM’s record for Diurnal Temperature Range (DTR).  DTR is the difference between daytime temperature (Tmax) and night-time temperature (Tmin). 

According to Dr Karl Braganza’s paper at https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2004GL019998 , “an index of climate change” is that DTR should decrease as greenhouse gases accumulate. To oversimplify, greenhouse gases will enhance daytime temperature while at night greenhouse gases will slow down cooling.  With increasing greenhouse gas concentration, daytime maxima are expected to increase, certainly, but the effect on night-time minima will be relatively greater.  Thus, minimum temperatures will increase faster than maxima, and DTR will decrease.  While Dr Braganza was referring to global values, Australia is a large dry continent where DTR should show up clearly.

We now have 111 years of temperature data in ACORN-SAT (Australian Climate Observation Reporting Network- Surface Air Temperatures).  In this post I only use Acorn temperature data and corresponding rainfall data.  Skeptics have been bagging Acorn ever since it was introduced, and for good reasons as you will see.

Figure 1 is straight from the Bureau’s climate time series page, and shows how DTR has varied over the years.  There is a centred 15 year running mean overlaid. 

Figure 1: Official plot of annual DTR

Melbourne, We Have A Problem… DTR has been increasing recently.

I have used BOM data to make plots that show this more clearly.  First, Figure 2 shows annual DTR from 1910 to 2020 has no trend.  It should be decreasing.

Figure 2:  Annual DTR

There appears to be a distinct step up around 2000-2002.

Figure 3 shows the same data for the last 70 years, broken into two periods, from 1951 to 2000, and 2001 to 2020.

Figure 3:  DTR since 1951

From 1951 to 2000, DTR behaves as it should, with a long term decrease.  After 2000, DTR steps up well above expected values.  The average from 1981-2000 is -0.12 C.  From 2001-2020 the average is +0.35C.  DTR suddenly increases by nearly 0.5C. Why?

DTR is very much governed by that other greenhouse gas, H2O.  Dry days, months and years produce hot days and cooler nights; wet periods result in cooler than average days and warmer than average nights.  This relationship is shown in Figure 4.

Figure 4:  DTR anomalies plotted against rainfall anomalies- all years 1910-2020

As rainfall increases, DTR decreases.  The effect is more marked in very wet (>100mm above average) and very dry (100mm or more below average) years.

Figure 5 shows time series of DTR (as in Figure 2) and rainfall.  Rainfall has been inverted and scaled down by a factor of 250.

Figure 5:  DTR and Inverted, Scaled Rainfall

There is close match between the two.

Using 10 year averages in Figure 6 makes the change after 2001 much clearer.

Figure 6:  Decadal means of DTR and inverted, scaled rainfall

The 10 year average rainfall to 2020 is about the same as the 1961-1990 average (the period the BOM uses for calculating anomalies).  The 10 year average DTR should be about the same value- not at a record level.

As DTR decrease due to greenhouse gas accumulation is caused by minimum temperatures increasing faster than maximum temperatures, Figure 7 shows 10 year averages of maxima and minima for all years to 2020.

Figure 7:  10 year running means of Tmax and Tmin

Tmax has clearly accelerated in the last 20 years, increasing much faster than Tmin.

This is NOT what should be happening: indeed it is the exact opposite of what greenhouse theory predicts.

Something happened to Australian maximum temperature recording or reporting early this century.  I suspect that the BOM changed from using the highest one-minute average of temperatures recorded in Automatic Weather Systems to the current highest one-second value for the day becoming the reported maximum; or else the design of a significant number of AWS changed, with new, faster-responding probes replacing old ones.

I also suspect I know why this was allowed to happen and continue.

Warmer minimum temperatures at night and in winter are not very scary, but record high temperatures and heatwaves make headlines.

It would suit the Global Warming Enthusiasts in the Bureau for apparently rapidly rising maxima and ever higher records being broken to make headlines, frighten the public, put pressure on governments, and generally support The Narrative.

But someone forgot to tell the left hand what the right hand was doing.

The result is that they are now faced with a contradiction- Diurnal Temperature Range is not decreasing as it should. 

The Bureau is either incompetent or has knowingly allowed inaccurate data to garble the record.

The World’s Biggest Thermometer

Are temperatures today unprecedented and dangerously high?  Apparently- the IPCC’s 6^th Assessment Report says that current temperatures are higher than at any time in the last 125,000 years

But that is wrong.  Temperatures today are cooler than they were in the past.

In making that statement I am not referring to data from ice cores (as in my previous posts here and here), but a simple and accessible temperature measurement device: the biggest thermometer in the world.

The following statements are uncontroversial:

1 Sea level rise is largely due to melting of glaciers and thermal expansion of the oceans.

2 Thermal expansion and glacial melting are symptoms of temperature increase.

3 Higher sea level indicates warmer conditions, lower sea level indicates colder conditions.

4 Sea levels are currently rising (by a small amount- NOAA says Fort Denison, Sydney, has a rise of 0.65mm per year).

5 This indicates temperatures have been rising.

6 But sea levels and therefore temperatures were higher than now about 4,000 to 7,000 years ago.

If you doubt point 6, you can easily tell whether it was warmer or cooler in the past relative to today.

How?  By looking for evidence of sea level change in areas that are not affected by tectonic rising or falling coastal land, or by large scale water run off or glacial melting, or by very large underground water extraction.

Areas such as the eastern coastline of Australia- the world’s biggest thermometer.

The continent of Australia is very old and flat.  It is in the middle of its continental plate with very little tectonic activity.  Australia’s coastlines are therefore largely stable with little vertical movement, apart from a small tilt down at the northern edge and a small uplift along the southern coast.  Australia is also a very long way from ancient ice sheets.

Evidence of higher sea level is plain to see in many places around Australia.  For example, at Phillip Island in Victoria, Victorian Resources Online describes raised Holocene beaches at Chambers Point, 0.5m and 3 to 5m above high water mark.  Arrows on this Google Maps image show where to find them.

More evidence at Wooloweyah Lagoon, near Maclean in NSW:

And Bulli, NSW:

There are many, many other locations where you can find Holocene beaches well above current sea level. 

Some of the height of these stranded beaches is probably due to the weight of deeper seawater from the melting ice sheets gradually tilting up continental coastlines as the sea floor deepened leading to an apparent drop in sea level at the coast.  However, as Lewis et al (2013) and Sloss et al (2018) (see Appendix below) show, this was of lesser importance especially in northern Australia.  Sea level fall was largely due to climatic influences- in particular, cooling and drying since the Holocene Optimum.

To conclude:  Sea levels were higher in the past, so temperatures must have been higher. 

Therefore there is no evidence that current temperature rise is anything unusual.  Just check the world’s biggest thermometer.

Appendix:  Here are a few of many references to higher Australian sea levels in the Holocene, and reasons for variation.

Sloss et al (2007)  Holocene sea-level change on the southeast coast of Australia: a review

“Present sea level was attained between 7900 and 7700 cal. yr BP, approximately 700—900 years earlier than previously proposed. Sea level continued to rise to between +1 and +1.5 m between 7700 and 7400 cal. yr BP, followed by a sea-level highstand that lasted until about 2000 cal. yr BP followed by a gradual fall to present. A series of minor negative and positive oscillations in relative sea level during the late-Holocene sea-level highstand appear to be superimposed over the general sea-level trend.”

ABC TV catalyst 19/6/2008

Even the ABC says sea levels were higher in the Holocene!

Lewis et al (2008) Mid‐late Holocene sea‐level variability in eastern Australia

“We demonstrate that the Holocene sea-level highstand of +1.0–1.5 m was reached ∼7000 cal yr bp and fell to its present position after 2000 yr bp.”

Moreton Bay Regional Council, Shoreline Erosion Management Plan for Bongaree, Bellara, Banksia Beach and Sandstone Point (2010)

“Sea levels ceased rising about 6,500 years ago (the Holocene Stillstand) when they reached approximately 0.4 to 1m above current levels. By 3,000 years before present they had stabilised at current levels”

Switzer et al (2010) Geomorphic evidence for mid–late Holocene higher sea level from southeastern Australia

“This beach sequence provides new evidence for a period of higher sea level 1–1.5 m higher than present that lasted until at least c. 2000–2500 cal BP and adds complementary geomorphic evidence for the mid to late Holocene sea-level highstand previously identified along other parts of the southeast Australian coast using other methods.”

Lewis et al (2013) Post-glacial sea-level changes around the Australian margin: a review

“The Australian region is relatively stable tectonically and is situated in the ‘far-field’ of former ice sheets. It therefore preserves important records of post-glacial sea levels that are less complicated by neotectonics or glacio-isostatic adjustments. Accordingly, the relative sea-level record of this region is dominantly one of glacio-eustatic (ice equivalent) sea-level changes. ….Divergent opinions remain about: (1) exactly when sea level attained present levels following the most recent post-glacial marine transgression (PMT); (2) the elevation that sea-level reached during the Holocene sea-level highstand; (3) whether sea-level fell smoothly from a metre or more above its present level following the PMT; (4) whether sea level remained at these highstand levels for a considerable period before falling to its present position; or (5) whether it underwent a series of moderate oscillations during the Holocene highstand.”

Leonard et al (2015) Holocene sea level instability in the southern Great Barrier Reef, Australia: high-precision U–Th dating of fossil microatolls

“RSL (relative sea level) was as least 0.75 m above present from ~6500 to 5500 yr before present (yr BP; where “present” is 1950). Following this highstand, two sites indicated a coeval lowering of RSL of at least 0.4 m from 5500 to 5300 yr BP which was maintained for ~200 yr. After the lowstand, RSL returned to higher levels before a 2000-yr hiatus in reef flat corals after 4600 yr BP at all three sites. A second possible RSL lowering event of ~0.3 m from ~2800 to 1600 yr BP was detected before RSL stabilised ~0.2 m above present levels by 900 yr BP. While the mechanism of the RSL instability is still uncertain, the alignment with previously reported RSL oscillations, rapid global climate changes and mid-Holocene reef “turn-off” on the GBR are discussed.”

Sloss et al (2018) Holocene sea-level change and coastal landscape evolution in the southern Gulf of Carpentaria, Australia

“ By 7700 cal. yr BP, sea-level reached present mean sea-level (PMSL) and continued to rise to an elevation of between 1.5 m and 2 m above PMSL. Sea level remained ca. + 1.5 between 7000 and 4000 cal. yr BP, followed by rapid regression to within ± 0.5 m of PMSL by ca. 3500 cal. yr BP. When placed into a wider regional context results from this study show that coastal landscape evolution in the tropical north of Australia was not only dependent on sea-level change but also show a direct correlation with Holocene climate variability….  Results indicate that Holocene sea-level histories are driven by regional eustatic driving forces, and not by localized hydro-isostatic influences. “

Dougherty et al (2019)  Redating the earliest evidence of the mid-Holocene relative sea-level highstand in Australia and implications for global sea-level rise

“The east coast of Australia provides an excellent arena in which to investigate changes in relative sea level during the Holocene…. improved dating of the earliest evidence for a highstand at 6,880±50 cal BP, approximately a millennium later than previously reported. Our results from Bulli now closely align with other sea-level reconstructions along the east coast of Australia, and provide evidence for a synchronous relative sea-level highstand that extends from the Gulf of Carpentaria to Tasmania. Our refined age appears to be coincident with major ice mass loss from Northern Hemisphere and Antarctic ice sheets, supporting previous studies that suggest these may have played a role in the relative sea-level highstand. Further work is now needed to investigate the environmental impacts of regional sea levels, and refine the timing of the subsequent sea-level fall in the Holocene and its influence on coastal evolution.”

Helfensdorfer et al (2020) Atypical responses of a large catchment river to the Holocene sea-level highstand: The Murray River, Australia

“Three-dimensional numerical modelling of the marine and fluvial dynamics of the lower Murray River demonstrate that the mid-Holocene sea-level highstand generated an extensive central basin environment extending at least 140 kilometres upstream from the river mouth and occupying the entire one to three kilometre width of the Murray Gorge. This unusually extensive, extremely low-gradient backwater environment generated by the two metre sea-level highstand….”