This was discussed in the latest episode of The Ezra Klein Show[1]. Apparently aerosols artificially held down temperatures roughly 1940–1980, after which they started to be reduced (from my memory of what they discussed). So it might be that the contribution of the greenhouse effect is masked in that period of the temperature graph.
1: https://www.nytimes.com/2023/09/05/opinion/ezra-klein-podcas...