In het bronartikel wordt een toelichting gegeven op deze relatief koude periode, citaat:
Look at the beginning of the 1940s in particular. See how in Europe there is a strong band of blue compared with the rest of the world.
This is quite a well-studied period that was probably linked to a large El Niño event - the climate cycle associated with shifting pressure patterns and a weakening of the trade winds in the Pacific.
The world warmed, apart from Europe which had a deep cold spell. And it probably had an impact on the outcome of WWII. The harsh winters at the time frustrated Hitler's armies as they invaded the Soviet Union.