For my younger readers, GIGO is an acronym for something that has been true in the past, is true now, and will be true forever: "Garbage In, Garbage Out". Case in point: NOAA and NASA temperature data.
There was a major station dropout — and an increase in missing data from remaining stations — which occurred suddenly around 1990. Just about the time the global warming issue was being elevated to importance in political and environmental circles.
A clear bias was found towards removing higher elevation, higher latitude, and rural stations — the cooler stations — during this culling process, though that data was not also removed from the base periods from which “averages,” and then anomalies, were computed.