The effect of changing Stevenson screens.
"While the designs of these screens have experienced some modifications during the ACORN-SAT period, the Bureau has
carried out tests that show the influence of these design changes on temperature measurements has not been material."
" However, throughout the last 100 years, Bureau of Meteorology guidance has allowed for a tolerance of ±0.5 °C for field checks of either in-glass or resistance thermometers.
http://www.bom.gov.au/climate/change/acorn-sat/documents/ACORN-SAT_IPR_Panel_Rep...The Stevenson screens have been reduced in size from 0.23m
3 to 0.06m
3.
"Short Communication
Impact of two different sized Stevenson screens on air
temperature measurements"
". The 1-year field experiment consisted of comparing air temperatures measured at the two most commonly sized Stevenson screens used by the Spanish Meteorological State Agency (AEMET) since last century; the medium-sized Stevenson screen employed at the second-order weather stations, versus the large-sized Stevenson screen mainly used at the first-order meteorological stations. The main objective was to report the air temperature difference between these two differently sized Stevenson screens, and to study the impact on the observed differences of some weather elements (i.e. relative humidity, wind speed, total cloud cover, atmospheric pressure and global solar radiation).
The results show that the medium-sized Stevenson screen tended to overheat daily maximum air temperatures (0.54 ∘C on yearly average) and also air temperatures recorded at 1300 UTC."
https://www.researchgate.net/publication/272494986_Impact_of_two_different_sized...BoM has been changing Stevenson screens to the smaller size.
And they ignore these biases.