This is an important point which I think should not be downvoted. You can review locations of the world's sensors using World Meteorological Organization's OSCA

This is an important point which I think should not be downvoted. You can review locations of the world's sensors using World Meteorological Organization's OSCAR system here: https://oscar.wmo.int/surface/ https://oscar.wmo.int/surface/ Note that "surface" is both land and ocean. It is used as opposed to satellite. On the other hand, while you were thinking about global averages, how come you didn't discover WMO's database? I think it is relatively easy to discover if you try just a bit.