An uncommon misperception about Australia's Angry Summer

It is very odd how many science deniers from Australia and the USA keep trying to deny the fact that last summer was the hottest on record for Australia.  This is despite all the evidence such as the dreadful infernos across most states, but particularly in Tasmania and NSW; and the searing heatwave across the continent in the first half of January.

Here is an animated chart showing mean and maximum summer temperatures from the Bureau of Meteorology. Click to enlarge:

Data Sources: BoM Mean Summer and Maximum Summer

Here is an animation of the temperatures across Australia in early January. Notice the huge areas above 39, 42 and 45 degrees Celsius:

Source: BoM

How could it be the hottest summer for Australia when it wasn't the hottest summer for any one state?

I've come across a couple of people who are wondering how can this past summer have been a record hot summer for Australia given that it was not a record hot summer for any state or territory.

Here is why that can be. 

This first chart shows the summer maximum temperatures for states and territories going back to 1999. Click to enlarge.  

Data Source: BoM

You can see that most years when some states were hot, others were cooler, even below the mean.  In 2012-13 on the other hand, it was hot everywhere at the same time.  The columns are all clumped up together.  So even though every state and territory had at one time a hotter summer, at no time have all states and territories been this hot all in the one summer.

In this next chart I've stacked the temperature anomalies so you can see it more easily. Note that these don't translate to the Australia-wide chart because the area of each state and territory differs.  They are purely to illustrate the fact that you can have no single "highest" but still have a "highest" in the aggregate.  (Click to enlarge.)

Data Source: BoM

You may have noticed that Australia has had cooler summers, particularly in 1999, 2001 and 2010.  To get some perspective on that, go back to the top chart, which goes back to 1910.  Here is a stacked chart of the States and Territories for the same time span.  I don't think we'll see a summer as cold as 1916 again, and probably not even one as cold as 1973 or 1975.

Data Source: BoM

The same proviso applies to this stacked chart.  It doesn't translate to the Australia-wide chart because the area of each state and territory differs.  It is purely for illustrative purposes.

If after that you are still not clear on how could it be the hottest summer for Australia when it wasn't the hottest summer for any one state, try this for yourself.  It's a matter of simple arithmetic.

Here's a series of numbers to illustrate.  It is sets of numbers grouped by year.  In all but the last two years, at least one of A, B, C, D or E has the maximum for all years.  Each one has a "record" highlighted.  Yet the average for Year 5 is greater than the average in any prior year even though none of A through E has a record in Year 5.

From the comments at WUWT

Most of my readers are probably wondering why I'm stating the obvious.  You would be surprised that some people don't "get" this.  Some examples:

Paul Homewood says:
June 29, 2013 at 3:56 am  Hottest summer or not, the facts are that not a single state recorded their hottest.

In a longer comment in which he complains at length about Tamino's article on this topic, Gonzo says:

June 29, 2013 at 10:28 am  BTW how many state heat records were broken during the “angry” summer? Oh none!

Which drew this response from Anthony Watts:

REPLY: there’s no point in paying attention to Grant Foster aka “Tamino” his rants are irrelevant – Anthony

Which is funny coming from someone who doesn't know a baseline from a waist line.