The GHCN US database has all the telltale signs of being complete garbage. Check out these graphs. The 1930s never existed.
Now compare vs. the raw USHCN data, which show the 1930s as being the hottest decade.
The divergence between GHCN US stations and USHCN US stations is massive.
But the real kicker for me is the divergence between airport and non-airport stations. This has all the telltale signs of intentional data tampering in the GHCN database. Patterns like that with sharp inflection points can not happen accidentally. Did the physical properties of airport stations radically change in 1950 and 1988? Something is seriously wrong with GHCN – which forms the basis of GISS.