evidence: Przybylak, R., Svyashchennikov, P.N., Uscka-Kowalkowska, J., and Wyszyński, P., Solar radiation in the Arctic during the early twentieth century warming (1921–1950): Presenting a compilation of newly available data, J. Clim., 2020, pp. 21–37. [...] Suo, L., Otterå, O.H., Bentsen, M., Gao, Y., and Johannessen, O.M., External forcing of the early 20th century Arctic warming, Tellus,Ser. A, 2013, vol. 65, no. 1, p. 20578. https://doi.org/10.3402/tellusa.v65i0.20578 [...] early 20th century warming global warming sea ice internal natural variability solar activity volcanism anthropogenic aerosols greenhouse gases