Saturday, February 11, 2017

Colour scale confusion in Australian heatwave maps


Forecast Map produced by Bureau of Meteorology for 5pm 11 February, 2017. Source


I am reflecting on how easy it is for misleading information to be circulated, even with the best of intentions. A UNFCCC tweet on the Australian extreme heatwave published on 10 February was factually misleading.

Let me explain the details.


The current extreme heatwave in south east Australia that is producing catastrophic fire conditions has maximum temperatures spiking in the 46C to 50C range. Yes they are extreme, and far above normal. Heat records are being broken.

A Climate scientist and a specialist researcher in heatwaves, Sarah Perkin-Kirkpatrick said that this “Heatwave is nothing short of horrifying”.

In 2013 the Bureau of Meteorology (BOM) added two colours - 50C to 52C and 52C to 54C - to the top of the legend as there was the possibility they may have been required. As it happens, conditions didn't quite match the forecast then and the extra colours were never used, except in that heatwave forecast. But the colours remained as part of the legend. (See my 2013 article on The colour purple: temperature scale upgraded to cope with heatwave)



So on February 7 this year Higgins Stormchasing, a 3rd party private meteorological service, produced this map of Australia - Welcome to Hell on Earth in Australia - showing temperatures in the high 40Cs. The legend on their map are completely different to the colour legend on the BOM maps. Within their own system they may be accurate, showing a massive purple hole consuming eastern Australia. But the map has no colour scale legend.



Higgins Stormchasing aren't the only ones using meteorological maps showing temperatures with a different colour scale to BOM. This image of a Channel 9 Newsreader with a temperature map has circulated widely. At least this map has a colour temperature scale associated with it.

Indeed I too have retweeted this image with what I thought was a pithy caption: "The #heatwave weather girl expression speaks so loudly of fear, incredulity, humour, anxiousness, and horror. Our #climate future".



But what people remember from a few years ago is the colour purple being added to the BOM temperature map.

So, the assumption when viewing the Higgins Stormchasing map, or the Channel 9 news map, is based on seeing so much purple that there is a terrifying increase in temperatures over a huge area. People are mentally comparing two maps coded with two very different colour scales.

The Higgins Stormchasing map then gets tweeted to the UNFCCC and WMO.

The UNFCCC then composes a tweet with the Higgins map image, but not identifying that it is a third party map unrelated to the Bureau of Meteorology. The factual problem comes in when the text accompanying the image refers to the colour scale change made by the Bureau of Meteorology in 2013. So this establishes a firm connection in readers minds between two different map scales that cannot be compared. Thus the factual error.

I came across a cut and paste Retweet on Friday evening, and immediately tried to highlight the problem.



This afternoon I came across the original @UNFCCC tweet in my timeline.



I wasn't the only one to raise this as an issue:



I responded and received a reply from WMO saying they source their map information from Bureau of Meteorology.

That is a relief.



So it seems whoever is in change of the @UNFCCC twitter account jumped the gun in sending out their tweet without doing a little fact checking and careful composition of the text. Here is @UNFCCC acknowledging the mistake.



How easy it is to cause confusion by texting before engaging our minds.

Perhaps we need a little reflection before hitting that send button.... or let the cartoonists and satirists out: