jennifer

After looking at hundreds of temperature series from different locations across Australia, I’ve come to understand that only cities show the type of warming reported by the IPCC, and other such government-funded institutions. Much of this warming is due to what is known as the Urban Heat Island (UHI) effect: bitumen, tall-buildings, air-conditioners, and fewer and fewer trees, means that urban areas become hotter and hotter.

For example, in a recent study of temperature variability and change for south-east Australia it is evident that maximum temperatures in the cities of Melbourne and Hobart are increasing at a rate of about 0.8 degree Celsius per century; while the rate of increase at the nearby lighthouses is half of this.

While the trend of about 0.4 degree Celsius per century at the lighthouses – as shown in Chart 1 – is arguably an accurate record of temperature change, the Australian Bureau of Meteorology changes this. To be clear, the Bureau changes a perfectly good temperature series from Cape Otway lighthouse by remodeling it so that it has Melbourne’s temperature signal – all through the process of homogenisation.

Government agencies in the USA have done exactly the same thing to temperature records for Colorado. This is all explained in detail in this new video by Monte Naylor:
 
https://vimeo.com/196878603/b9ea716a74

The video runs for about 40 minutes, and is quite technical.

The conclusions from this study have been summarized by Monte as follows:

(1) The USHCN Fort Collins station temperature record was not recognized by NOAA as having the heat bias from expanding UHI which has been easily identified by other researchers.

(2) NOAA’s homogenization program adjusted the USHCN Boulder station temperature history in a fashion that does not match any of the four other nearby rural/suburban long-term temperature histories. Nor does the NOAA-homogenized Boulder temperature history resemble the average temperature trend found by this study.

(3) NOAA’s homogenization program adjusted the Boulder temperature history to resemble the UHI-contaminated temperature history of the Fort Collins station.

(4) The best estimate of the northern Colorado Front Range temperature trend is obtained by using the TOB-adjusted Group of 5 average which shows a warming temperature trend of 1.7 °F (0.95 °C) from 1900 to 2015. The NOAA temperature trend, about 4 °F over 115 years, is more than twice the best estimate of this study.

(5) About 70% of the warming shown in the Group of 5 average temperature trend occurred before 1932. Temperatures trends of recent decades do not show anomalous warming.  Distinct warm temperature events occurred in the 1930’s and 1950’s that were much warmer than those observed since the turn of the 21st century.

(6) The Northern Front Range Group of 5 average temperature trend does not increase in a fashion consistent with increasing atmospheric carbon dioxide.

Media reports yesterday claimed that 2016 was another record hot year. However, close scrutiny of all the temperature data from the state of Victoria paints quite a different picture. When all 289 temperature series from Victoria are simply combined, the hottest years are in the early part of the record. In particular, 1914 is very evidently the hottest year on record – see blue time series in Chart 1. This finding builds on a recently published book chapter focused on south-east Australia, and is part of a larger study working towards a realistic reconstruction of Australia’s temperature history.

Yesterday the Australian Bureau of Meteorology released its Annual Climate Statement, claiming 2016 to be the fourth-warmest year on record for Australia – and also an unusually wet year. Wet years are usually much cooler years, but because the overall trend in the ACORN-SAT* time series shows significant warming, even a wet year comes out as relatively hot.

Of course there is no one place in Australia where the average temperature can be measured; so the Bureau relies on a reconstruction to determine how hot 2016 was, relative to the historical record. Their method, however, is quite subjective in terms of choice of locations to include, the method used to remodel the individual temperature series before they are combined (this is refered to as homogenisation*), and the area weighting applied – with the weighting changing on a daily and monthly basis.

Late last year, I had a book chapter, co-authored with John Abbot and published by Elsevier*, which shows historical temperature trends for south-east Australia from 1887 to 2013 based on a more transparent system – that can be easily replicated. We choose the longest continuous series, used the same series to calculate every value, and applied an area weighting based on topography and landuse – and did not remodel individual temperature series. In the chapter we conclude that temperature trends for south-east Australia are best described as showing statistically significant cooling (yes cooling) of 1.5 degree Celsius from 1887 to 1949, followed by warming of nearly 2 degrees Celsius from 1950 to 2013. The warmest year in this reconstruction is 2007, followed very closely by 1914.

A colleague at the University of Tasmania, Jaco Vlok, has compared our south-east reconstruction with a reconstruction based on all 289 temperature series for Victoria – but only from 1910. The different methodologies used to generate these reconstructions, and also the official ACORN-SAT series for Victoria, which is the series used by the Bureau to calculate the official statistics for Australia, are detailed in Table 1.

There is a very high degree of synchrony between the reconstructions, though when all the raw data is simply combined – Vlok’s approach – the hottest years are all in the earlier part of the record: 1914 (hottest) followed by 1919, 1921, 1938, 1961 and then 2014.

Postscript: I have expanded on this analysis in an article just now published by Graham Young at OLO. Jennifer, Noosa, Monday 9th January, 2017.

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* ACORN-SAT stands for Australian Climate Australian Climate Observations Reference Network – Surface Air Temperature and is a dataset developed by the Bureau based on a subset of available temperature series, almost all homogenised, and then combined with an area weighting and used to report climate variability and change. The annual climate statement for 2016, based on this ACORN-SAT dataset, is here: http://media.bom.gov.au/releases/333/2016-a-year-of-extreme-weather-events/

* Homogenisation involves changes to measured temperature values ostensibly to correct for non-climatic variables. These changes to the observational data are quite different from quality assurance. For example, the need for homogenisation most often results from a ‘statistical test’ detecting a break point, these breakpoints often occur after a period of missing data. In response all values preceding the breakpoint are often reduced by a specific amount back to 1910. The amount by which the measured observational values are reduced is determined through the application of algorithms and calculated relative to what are referred to as ‘neighbouring’ stations, which may be Urban Heat Island (UHI) effected, and/or located many hundreds of kilometers from the target location.

* Marohasy, J. & Abbot, J. 2016. Southeast Australian Maximum Temperature Trends, 1887–2013: An Evidence-Based Reappraisal.  In: Evidence-Based Climate Science (Second Edition), Pages 83-99. http://dx.doi.org/10.1016/B978-0-12-804588-6.00005-7 You can read more about this series here: https://jennifermarohasy.com.dev.internet-thinking.com.au/2016/12/temperatures-trends-southeast-australia-1887-part/

Charts that show year-on-year increases in temperature have become a symbol of all that is wrong with the world – or at least modernity and Western Civilization. So, why then, when such a chart was shown to a studio audience of opinion leaders, did it caused them to break-out in spontaneous applause? The Sydney Q&A audience could not conceivably have been applauding global warming – more likely this audience was applauding the affirmation that was being afforded their belief in global warming?

 

Of course, the chart that particle physicist Brian Cox held-up to the audience (as shown in the above Youtube video) is an historical reconstruction. There is no one place on Earth where the world’s temperature can be measured – and this particular chart is based on a variable number of homogenised temperatures series. By ‘homogenised’ I mean remodelled – ostensibly to ensure “non-climatic influences are minimised”; but in the process trends are changed.

I’ve just had a book chapter, which I co-authored with John Abbot, published that shows historical temperature trends for southeast Australia back to 1887 – using unhomogenised temperature series.

This reconstruction is shown by the purple line in Chart 1 (see below). It suggests a rate of warming less than half that shown in Cox’s global homogenised reconstruction; and might be better described as exhibiting considerable inter-annual variability – with cycles of cooling and warming.

The method used to develop this reconstruction perhaps represents an important first step in developing an Australian-wide reconstruction based on un-homogenised data.

Our chapter concludes that the series for southeast Australia is best described as showing statistically significant cooling (yes cooling) of 1.5 degree Celsius to 1949, followed by warming of nearly 2 degrees Celsius to the present. (If you would like a pdf copy of the chapter, email me: j.marohasy at climatelab.com.au).

The official Bureau of Meteorology reconstruction for the state of Victoria is shown in red in Chart 1; and is based on ACORN-SAT. The homogenised ACORN-SAT database only begins in 1910. It is used by the Bureau, and also CSIRO, to report climate variability and change. Eleven locations are used in the ACORN-SAT reconstruction for Victoria – with some of the series from these locations very short, and with a lot of missing data; all were remodolled.

Our southeast reconstruction is based on the same five long and continuous series with only three adjustments made to two of the series (Deniliquin and Cape Otway) to correct for equipment changes in 1908 and 1898 – as detailed in the chapter.

Despite the very different methodologies used, the reconstructions are surprisingly similar. Both reconstrucions show considerable inter-annual variability, with almost synchronous peaks and troughs: see Chart 1. In both reconstructions, 2007 is the hottest recent year, though temperatures were almost as hot back in 1914. In large part because the ACORN-SAT database only starts in 1910, which corresponds with a dip in the record, this official series for Victoria indicates an overall rate of warming of 0.9 degree Celsius per century – compared to 0.3 degree Celsius for the southeast reconstruction.

Both reconstructions are of maximum temperatures. Global warming is typically reported as an increase in the mean temperature, which is the average of the maximum and minimum temperatures. The maximum temperature is the daytime temperature; and an arguably better measure of regional temperature variation because of the higher rates of turbulent mixing of the atmosphere during the day time.

In Chart 1, I’ve also plotted temperature maxima as measured at the agricultural research station near Rutherglen in northern central Victoria – this is the series shown in yellow. This is an exceptionally high quality series because it has been measured using standard equipment at the same rural site for over 100 years. But it was not part of the southeast reconstruction because we only used series that began on, or before, 1887 for the southeast reconstruction.

Temperature minima and maxima do not always trend in the same direction. In the case of Rutherglen, temperature minima actually show cooling – consistent with other series from this region. This cooling is most obvious in spring, and probably associated with the extensive development of irrigation. Through the homogenisation process the Bureau change the cooling in the Rutherglen temperature minima to warming before including Rutherglen in the official ACORN-SAT database. I’ve written extensively about this, including in a recent research paper entitled simply ‘Temperature change at Rutherglen in south-east Australia’.

Key Reference/New book chapter

Marohasy, J. & Abbot, J. 2016. Southeast Australian Maximum Temperature Trends, 1887–2013: An Evidence-Based Reappraisal.  In: Evidence-Based Climate Science (Second Edition), Pages 83-99. http://dx.doi.org/10.1016/B978-0-12-804588-6.00005-7

The wild, wet weather across southern Australia this spring is a consequence of an unusually strong temperature gradient, especially evident in the following chart as warm water to the north of Australia (especially in the Timor and Arafura Seas), and the cold waters off the southwest of Australia.

Former head of Australia’s National Climate Centre, Bill Kininmonth, recently emailed me:

The warm water has increased the supply of moisture feeding into the airflow over Australia. The moisture increases by nearly 7 percent with each degree C temperature rise. The cold water to the south and west of Australia tightens the temperature gradient and increases the potential for storm development (technically it is called increasing baroclinic instability). It is normal to have a period of tightening temperature gradient during spring time – the nearby ocean and land of southern Australia are cold after winter but the approach of summer is warming ocean and water of north Australia. Because of this annual tightening of the gradient, spring is the wettest period with often strong storms over southeast Australia. This year has been particularly wet and stormy because of the pattern of sea surface temperature anomalies. It is not climate change.

As the oceans have a critical influence on land temperatures, this same pattern is evident in the surface temperature data for Western Australia. While Perth has had its coldest September on record, it’s actually been very warm in the north of the state.

A colleague has plotted the following fascinating chart which shows a running yearly average of mean temperatures from 180 sites as recorded by the WA Agriculture Department.

The top line is Kununurra, in the far north, showing temperatures are still rising. The next line is Carnarvon. The great mass of lines are the southwest corner of WA from just north of Geraldton to east of Esperance and these show temperatures are all falling. The coldest lines are at elevated places like Mt Barker. The brown line starting around 2008, and at 16.7C, is South Perth.

There is a remarkable consistency about the southwest corner where the coolest 12 months ended in mid-2006 and the average then climbed around 2.5C to a peak in late 2014 and has dropped by a little over 1C since then.

So what happens next?

The water to the far northwest is very warm as can be seen by the rise in Kununurra surface temperatures, and the orange in the NOAA sea surface temperature map.  The Leeuwin current that brings the warm water down the coast is normally weakest in the summer months and strongest over the autumn and winter.