Daily data for global sea ice extent, Arctic sea ice extent, and Antarctic sea
ice extent used for the C3S monthly Climate Bulletins come from the Sea Ice
Index v2.2 (OSI-420) produced by EUMETSAT OSI SAF. Data should be downloaded
from their website: https://osisaf-hl.met.no/v2p2-sea-ice-index

Scroll down to the bottom of the page to find links to the netcdf files. The
page also provides a link to the ftp server where TXT files (similar to CSV)
can be downloaded.