Likely you will find GlobalSnowMap.tiff in Lib/python/site-packages/sen2cor/aux_data. In this folder, addd the following files from the archive, that you might have to extract from their (.tar) archives:
ESACCI-LC-L4-LCCS-Map-300m-P1Y-2015-v2.0.7.tifESACCI-LC-L4-WB-Map-150m-P13Y-2000-v4.0.tif- Snow Condition folder:
ESACCI-LC-L4-Snow-Cond-500m-P13Y7D-2000-2012-v2.0, with all theSnow_Cond...tif’s.
Your next sen2cor run will no longer complain about missing files.