Why was there a negative temperature anomaly between 1950 to 1980? If I understand the information from this link correctly,
Instrumental temperature record
between 1950 to 1980 there were negative temperature anomalies in the years of those decades.




decade
difference (°C)
difference (°F)




1950–1959
−0.02
-0.0360


1960–1969
−0.014
−0.0252


1970–1979
−0.001
−0.0018




This seems odd considering massive oil consumption started in 1880 IIRC, and by 1980 over 350 billions of oil barrels were already consumed (much more probably, since the data before 1950 isn't considered because there weren't reliable records).
Why was there a negative temperature anomaly between 1950 to 1980?
This phenomenon is known as global dimming.

It was due to the particles and aerosols mostly released by combustion of fossil fuels such as diesel. Those particles block the radiation from the sun, so they have a cooling effect. For some decades this effect counterbalanced the warming effect of greenhouse gases, although it is no longer the case at a global scale (see for instance Wild et al. 2007). Particles emission has been reduced thanks to better engines and new regulations, which stopped their masking effect on global warming. Which is a good thing since those particles have a serious impact on health.