Why Aren’t All Maximum Temperatures Official?

Yesterday (January 15, 2019), a photo was distributed with the town thermometer recording a temperature of 52C in Port Augusta – yet the official maximum was ‘only’ listed as 48.9C.  Temperatures around the globe are measured to a standard set out by the World Meteorological Organisation and must be measured in a box called a Stevenson Screen.

The first and foremost reason for this is to ensure consistency.  If all temperatures are measured the same way in the same conditions, then all temperatures can directly be compared with each other.  This means if we record a temperature in Port Augusta, then it can be directly compared with a temperature in Marble Bar, Sydney or even overseas such as London!  


An example of a Stevenson Screen (source Bureau of Meteorology).  All official temperatures are measured in these boxes.

Thermometers are often placed everywhere around houses and most cars even report the outside temperature now too.  However they can fluctuation greatly.  For instance, a parked car is likely to read much higher than a moving car, while the wall of a house could be radiating heat (particularly at night) which will artificially inflate the temperature.

This doesn’t mean the temperature isn’t real, the physical temperature is the temperature displayed on the thermometer – but it can’t be compared with another temperature elsewhere.  For instance, we can’t say that because the car says it’s 40C in Sydney, but some one’s verandah in Alice Springs says it’s 38C that it’s hotter in Sydney because they’re measured differently.  

Measuring temperatures by Stevenson Screen ensures consistent results – which is crucial for record keeping and statistics.  So if you’ve ever wondered why your temperature differed to the official temperatures listed by the Bureau of Meteorology you now understand why!

An example of differing temperatures in the same area depending on the method of measurement.