The International Geophysical Year (IGY), 1957–1958, involving sixty-seven nations and initiated by ICSU.
The record calls it a low-priority side project of the IGY.
The IGY is publicly presented as a major international effort. It brought together scientists from more than 60 countries for coordinated observations. During it, Sputnik 1 was launched. But the first CO2 measurements, now known as the Keeling curve, were hosted as a low-priority side project. The record does not establish any command or funding relationship between the IGY and Keeling, nor that ICSU directed the measurements or their conclusions.
It shows how a public event can be known for one thing while a quiet side project produces a different, lasting result.