Global Historical Climatology Network
NOAA Global Historical Climatology Network is a collection of hourly weather data put together from multiple weather services around the world, even those where at this moment no data is publicly offered. Resolution is fixed on daily, because this is the most common and maintainable resolution with most observations practiced all over the world.
The dataset originally doesn’t contain average daily temperature, which is why this data is calculated by wetterdienst with
so those values are not actually averages but means.