Global averages are calculated from the averages for each of the two hemispheres, so these few stations have a large influence on what's supposedly “global”.
In much of the 1860s and 1870s most of the supposedly global coverage was from Europe and its trade sea routes and ports, covering only about 13% of the Earth's surface.
When a thermometer is relocated to a new site, the adjustment assumes that the old site was always built up and “heated” by concrete and buildings.
During that period global coverage is low – it averages 30% across that time – and many land-based temperatures are very likely to be excessively adjusted and therefore incorrect.
However, this hardly stops ignorant politicians from declaring that the IPCC's claim of attribution is tantamount to unambiguous proof of coming disaster Cherry picking is always an issue.