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In the Arctic, observed decadal mean surface air temperatures (SATs) were 0.70°C–0.95°C lower around 1970 than those around 1940. The 35‐multimodel ensemble mean of historical simulations in the Coupled Model Intercomparison Project Phase 6 (CMIP6) exhibited Arctic surface cooling trend in 1940–1970, which could be attributed to external forcings. Multimodel ensemble means of CMIP6 Detection and Attribution Model Intercomparison Project historical simulations exhibited Arctic surface cooling of −0.22°C (±0.24°C) in 1970 versus 1940 and showed that anthropogenic aerosol forcings contributed to a cooling of −0.65°C (±0.37°C), which was partially offset by a warming of 0.44°C (±0.22°C) due to well‐mixed greenhouse gases. In addition to the anthropogenic aerosol forcings, multidecadal internal variability with a magnitude of 0.47°C was the component primarily contributing to the observed Arctic cooling. We identified a spatial pattern of pan‐Arctic multidecadal cooling due to the internal variability that resembles the 1940–1970 cooling pattern. Plain Language Summary: Instrumental records show Arctic surface cooling during the mid‐20th century (1940–1970) followed by ongoing rapid warming since 1970. Long‐term global warming has been extensively researched and has been primarily ascribed to anthropogenic greenhouse gas forcing. However, the factors contributing to the mid‐20th century Arctic surface cooling remain poorly constrained. In this work, multimodel analyses using state‐of‐the‐art climate models suggest that external factors may have contributed to the high‐latitude surface cooling observed in 1940–1970. Further analysis shows that both increased anthropogenic aerosols and multidecadal internal variability provide major contributions to the 1940–1970 Arctic surface cooling. By analyzing surface cooling via unforced long‐term climate simulations, we identified a spatial pattern of pan‐Arctic multidecadal cooling, similar to the observed cooling pattern in the Arctic during 1940–1970. Key Points: Most Coupled Model Intercomparison Project Phase 6/Detection and Attribution Model Intercomparison Project models represent the observed multidecadal surface cooling trend during the mid‐20th century (1940–1970) in the ArcticAnthropogenic aerosol forcing and multidecadal internal variability are the major components contributing to the 1940–1970 Arctic coolingWe identify a spatial pattern of pan‐Arctic multidecadal cooling due to internal variability that resembles the 1940–1970 cooling pattern [ABSTRACT FROM AUTHOR]