A thermometer shelter is a protective enclosure that keeps a thermometer safe from outside influences like sunlight and wind, so it can accurately measure and display the temperature. Full definition
A change in the type of thermometer shelter used at many Australian observation sites in the early 20th century resulted a sudden drop in day time temperature an increase in minimum temperatures which is entirely spurious. (bom.gov.au)
So anthropogenic land use changes (which are strongly biased toward deforestation and desertification) tend to raise the temperature observed at thermometer shelters around the world, while at the same time they tend to reduce the amount of energy available to warm the atmosphere above the surface. (realclimate.org)
However, due to different locations, elevations and thermometer shelters, Perth Botanic Gardens records are thought to overestimate temperatures by approximately 04C. (waclimate.net)