A large discontinuity in the mid-twentieth century in observed global-mean surface temperature
Data sets used to monitor the Earth's climate indicate that the surface of the Earth warmed from 1910 to 1940, cooled slightly from 1940 to 1970, and then warmed markedly from 1970 onward. The weak cooling apparent in the middle part of the century has been interpreted in the context of a variety of physical factors, such as atmosphere